GEOLOGICAL SURVEY OF NEW SOUTH WALES DEPARTMENT OF MINERAL RESOURCES AND DEVELOPMENT N. L. MARKHAM, DIRECTOR GEOLOGV OF THE MICHELAGO ~:~DDJDDD SHEET 8726 BY S. J. RICHARDSON Price: $9.00 Manuscript dated June 1976 Issued under the authority of the Hon. R. J. Mulock, LL.B. M. P., Minister for Minerai Resources and Development 11""111111""I"'" "'" "1111"11 "III"'"""""R00047928 - 1111111111111111111111111111111111111111111111111111111111II 0004941710 National Library of Australia card number and ISBN o 7240 1246 X PUBlICATIOIiS IN THE 1:100.000 GEOLOGiCAl SHEET SERIES TaralgA 1:100,000 Geoloq1cal Sheet 8829 (1973) Drake 1:100,000 Geological Sheet 9340 {1974} Naxooma 1:100,000 Geological Sheet 8925 (1975) Toxrowangee - ftNleclI Gap 1: 100.000 ..oologl.clll Shut 713S - 12)5 11975) Cootamundra 1 100,000 Ceologlcal Sheet 6528 (1975) Bral.cwood 1:100,000 Geological Steet 8827 (1975) YA•• 1:100,000 ~eol09l.cal She~t 8628 (197S) COboe I:iOC,OOO r~oloqical Sheet a035 II9?7) Michelago 1:100.000 GeQloq1cal Sheet 872 (1971) .~. ,,' . ". "h'" ,rF.~~~-" "f~" .. _. " \'- .. .~~ ... .. ".... '." '... '.. "" ....1-..... ,~ ," •• '0401' ....t~· ." .•"",L .... oUO .... I-' .. ,..;: .. r-:-.I_ · ...~.. .- .. . ._. _.. -.. . '.' s- .. .~ ." '.. .. .. .. '..... •.. ' .... ......... ....'... ..••• I, • ... ... ....." ~.'::;: .... 'oJ ........' _.'.OJ., ...... . ........' .. .•.:'~/;::-;S··~~}." . 0&,••• .. , .. ............... ... "" ............ ... .. n .. ....... .. ..... OJ .... .._....~ ...... "....... ):::- '" '....,'1-."'''" ........... ........... ._ ... .. ...... I- ••h :o:~ ...... j" ~.. .. ~ · ••i!o. ":'_"." ";:'::........_.... .... '....... '')0 II ...... ...... . ............ ........... .. ...... ..... 'n..... ....... , 'I. ..··t' ..+ ...• ..... .. • >:1 .~~....~ ... ....,:"1', .....""; ... .m;','" .h..~" ...... ._. .... ;, ......... ' .....0 ~""""O:OO I.;:;;"'I.. n",w "........ "" 'UI "" II "" '1 UII .." .. ""'-11 .. ' ........ '"~ " .., ",'m,'" ' "', .,,' !'., ...' ...." ..II .'11 ./1 Of" ...' ..., .... "11 ...'''''!~~n.. L~:" " . ,p..., · ".T-~ ""1"" ... ._. • ...1 0 ,... I ..... ·'........ '.. '.. '.. ". '..... _,'.01• ....... .,.... "... ......'. ,j;4~'Nj ". '" "..-" ... ,." _." ..... • .QO.0lII _ ..".no .... ......,..4, ..~~ • ."". · . I,,;:'''''" .: ~:. ;~..,.; ::. ...........:...• ... ...~ ...- ......- .... ,. "1~'" .', ..., ....1- ..... UI' ... , _ .......... ,,/0, "r" .!":" "" ~.•.~..:. ......... . ~:::i.' .., ~"....~ ... ........- • •• ~.. ' ., , ;"1·· .. • It In>~1• .:1.''' .....:: ..nff • • ' .. I' •• . ::~i...: "ot" .." .... • .. , • ..,.~':~l' .... '" • • mmlill [II n~ ~I II] ~ 0004941711 Frontispieae: HighZy sheared, aZeaved tuffs in the CoZinton VoZaanias to the south of the Bredbo River at GR 940170 111111111111111111111111111111111111\1111111111111111111\111 0004941720 CON TEN T S INTRODUCTION Location Cultural features Field methods Climate vegetation Soils Land use Previous literature Physiography Future wcrk GEOLOGICAL SETTING ORDOVICIAN TO EARLY DEVONIAN STRATIGRAPHY ORDOVICIAN Cotter Anticlinorium Adaminaby Beds Cullarin and Rocky Pic Anticlinoria Foxlow Beds EARLY SILURIAN Cullarin Anticlinorium Ryrie Formation Gungoandra Siltstone Member MIDDLE SILURIAN TO EARLY DEVONIAN Canberra Synclinorium .. Cappanana Formation Colinton Volcanics .. Tuggeranong Tuff Member Williamsdale Volcanics Bransby Beds Captains Flat Synclinorium .. Hoskinstown Group .. Copper Creek Shale .. Rutledge Quartzite Member .. Kohinoor Volcanics .. Carwoola Formation .. Captains Flat Formation Yandyguinula Member Sinclair Conglomerate Member INTRUSIONS SILURIAN PAGE 1 1 1 3 3 3 5 5 6 7 11 13 21 21 21 21 26 26 30 30 30 31 33 33 33 38 43 45 48 55 55 56 57 59 64 65 67 68 71 75 1111111111111111111111111111111111111 11111111111111111111111 0004941730 vi Cotter Anticlinorium Murrumbidgee Batholith Contaminated Phases Clear Range Granodiorite Murrumbucka Tonalite Callemondah Granodiorite uncontaminated Phases .. Shannons Flat Adamellite Tharwa Adamellite Leucogranites Booroomba Leucogranite SILURO - DEVONIAN Canberra Synclinorium Livingstone Porphyry .. Bullanamang Porphyry •. Cosgrove Porphyry DEVONIAN Cullarin Anticlinorium Michelago Igneous Complex Northern Michelago Body Monkellan Granodiorite Onslow Granodiorite Micaligo Adamellite .• Minor phases Southern Michelago Body Koolambah Adamellite Minor phases Sapling Flat Igneous Complex Danswell Creek Granodiorite Wangrah Adamellite Other Igneous Bodies Bredbo River Adamellite Tinderry Granite Harrisons Peak Granite Urialla Granite Watch Box Granite Good Good Adamellite .. Minor acid to intermediate intrusions including unnamed small porphyries Rocky Pic Anticlinorium Jerangle Igneous Complex Anembo Granodiorite .. Towneys Creek Adamellite Boro Granite PERMIAN(?) CAINOZOIC PAGE 75 75 78 78 79 81 81 81 82 83 84 85 85 85 86 88 89 89 89 91 92 93 94 95 95 95 96 97 100 101 103 103 105 107 109 110 112 112 114 114 116 117 119 121 123 vii Cainozoic Sediments Tertiary Quaternary Undifferentiated Cainozoic Sediments Cainozoic Basic Rocks .. Tertiary Whinstone Basalt Undifferentiated Basic plugs Basic dykes PALAEOENVIRONMENTS Ordovician Early Silurian Late Silurian STRUCTURES AND METAMORPHISM Molong - South Coast Anticlinorial Zone Cotter Anticlinorium Cullarin Anticlinorium Rocky Pic Anticlinorium .. Cowra - Yass Synclinorial Zone Canberra Synclinorium Captains Flat - Goulburn Synclinorial Zone Captains Flat Synclinorium Conclusions GEOLOGICAL HISTORY Lachlan Pre-Cratonic Province Benambran - Quidongan Tectonic Stage Bowning Tectonic Stage Tabberabberan Tectonic Stage Kanimblan Tectonic Stage Tasman Epi-Cratonic Province Permian Tectonic Stage Late Cretaceous - Cainozoic Tectonic Stage ECONOMIC GEOLOGY Metallic minerals Construction materials Railway ballast Clay Sand Gravel Limestone ACKNOWLEDGEMENTS SELECTED BIBLIOGRAPHY PAGE 123 123 123 123 124 124 124 125 125 126 129 129 130 130 133 136 136 137 141 143 143 144 144 145 147 147 147 150 151 151 151 151 152 153 153 154 154 154 154 155 155 156 157 viii APPENDIX 1 - FOSSILS RECORDED FROM THE MICHELAGO 1:100,000 SHEET AREA APPENDIX 2 - SELECTED PETROLOGICAL DESCRIPTIONS APPENDIX 3 - MODAL ANALYSES, CHEMICAL ANALYSES, AND C.I.P.W. NORMS OF SELECTED ROCKS FROM THE MICHELAGO 1:100,000 SHEET AREA APPENDIX 4 - AGE DETERMINATIONS INDEX PAGE 177 201 215 241 245 ix I LLUSTRATI ONS FIGURES PAGE Figure 1. Southeastern New South Wales, showing the location of the Michelago 1:100,000 sheet 2 Figu:re 2. Thesis areas on the Michelago 1:100,000 sheet 8 Figu:re 3. Sketch map showing physiographic units and cultural features on the Michelago 1:100,000 sheet 9 Figure 4. Stratigraphic section of the Cappanana Formation and part of the overlying Colinton Volcanics opposite page 36 Figure 5. Sketch map showing relationships between the various facies of the Colinton Volcanics 40 Figure 6. Structural map of New South Wales showing the position of the Michelago 1:100,000 sheet 133 Figure 7. Schematic structural map of the Michelago 1:100,000' sheet 134 Figure 8. Structures developed in the Ordovician Foxlow Beds in a road cutting on the Bredbo - Jerangle road PHOTOS Frontispiece Highly sheared, cleaved tuffs in the Colinton Volcanics to the south of the Bredbo River 139 PAGE ii Photo 1. A view of the London Bridge limestone arch .• 35 Photo 2. Exposure of an unconformable contact between the Cappanana Formation and the Foxlow Beds on Burra Creek near its junction with the Queanbeyan River 37 Photo 3. Photomicrograph of a welded rhyolitic crystal tuff in the Colinton Volcanics 42 Photo 4. Sheared limestone and tuff units of the Bransby Beds lying adjacent to the Murrumbidgee Fault and Clear Range Granodiorite 50 Photo 5. Bedding and angular tuff fragments in tuffaceous sediments of the Bransby Beds 52 x PAGE Photo 6. An intrusive contact between the Livingstone Porphyry and southward-dipping tuffs of the Bransby Beds 54 photo 7. Intrusive contact between the Michelago Igneous Complex and the Ordovician Foxlow Beds, present in a road cutting on the Bredbo - Jerangle road 90 photo 8. Extensive quartz reefs along the line of the Collingwood Fault near "Collingwood" homestead 92 Photo 9. A partly digested chevron-folded sedimentary fragment in the Sapling Flat Igneous Complex 102 Photo 10. View of the Tinderry Granite, the Foxlow Beds, and the Michelago Igneous Complex .. 106 photo 11. Disharmonic fold developed in Ordovician black chert and sandstone 140 Photo 12. Refolded fold developed in the Foxlow Beds near the Boro Granite 142 Photo 13. Kinking developed in siltstones and tuffs of the Colinton Volcanics 144 photo 14. Deformation in black cherts in the Foxlow Beds in outcrop on the Bredbo - Jerangle road 149 TABLES PAGE Table 1. Rainfall data for selected locations within the Michelago 1:100,000 sheet area .. 4 Table Table Table 2. Regional stratigraphic correlations 3. Local stratigraphic correlations •• 4. Stratigraphy of the Michelago 1:100,000 sheet 16 18 23 Table 5. Some chemical properties of I-type and S-type granites 71 Table 6. Some petrological, field relationshi~ and economic characteristics of I-type and S-type granites 72 Table 7. Classification of granites into I-type or S-type on the basis of chemical and petrological characteristics 74 I NTRODUCTI ON Location The Michelago 1:100,000 sheet covers an area of some 2497 km 2 in the State of New South Wales and the southeast portion of the Australian Capital Territory. The boundaries are defined by latitudes 35°30' and 36°S, longitudes 149° and 149°30'E, locating the area between Cooma and Canberra, approximately 280 km southwest of Sydney (figure 1). Cultural Features Access is good to moderate, with two primary roads running north - south through the area. The Monaro Highway links Bredbo and Michelago to Canberra and Cooma, and the Captains Flat road joins Captains Flat and Jerangle with Queanbeyan and Bungendore. Several east - west gravel roads serve to connect the abovementioned roads. A network of farm tracks and fire trails provides access to most parts of the area, although many of the latter are only suitable for four wheel drive vehicles. The Goulburn - Bombala railway line traces a path adjacent and roughly parallel to the Monaro Highway, while further to the east a spur line from Bungendore to Captains Flat is disused. Some landing facilities for light aircraft are available, mainly in the vicinity of Captains Flat. The population is concentrated in or near the villages of Captains Flat, Tharwa, Bredbo, Michelago, Jerangle, Colinton, Williamsdale, and Royalla, the first four being by far the largest in size. Farms cover most of the area in New South Wales, although a nature reserve is proposed for the district centred on Tinderry Peak (the Tinderry Mountains Nature Reserve). Within the Australian Capital Territory a policy of Commonwealth ownership of all property has led to the general conversion of most freehold property to leasehold with the associated discouragement of all farming and mining activities. Consequently, many properties are now unoccupied and the population is centred in Tharwa, close to Canberra. Telephone communications and power are sup~lied to most of the farms in the area, although there still remain a few places away from the main roads that have neither. Three microwave towers have been constructed for the purposes of long-distance communication and these are found at Mount Roberts (GR 825159), Cosgrove Hill (GR 938151), and to the east of Williamsdale (GR973617). The construction of dams on a large or medium scale has been restricted to the old mine water supply dam at Captains Flat and the proposed dam at Googong on the Queanbeyan River just to the north of London Bridge; the Googong dam is to provide an additional source of water for the expanding city of Canberra. N·.lmerous small farm dams have been constr'1cted, particularly in areas close to the main roads where more clearing of land has taken 111111111111111111111111111111111111111111111111111\111\1111 D004941740 2 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET 151°E SCALE 0 25 50 100 -- Kilometres • Cootamundra Location of Mlchefago 1: 100,000 sheet Oberon • Brohn Hill 10508 Figure 1. Southeastern New South Wales, showing the location of the Miche1ago 1:100,000 sheet o 1 234 5 ..' -_.'...._....I'l.........l'l.._...1'__-1J em INTRODUCTION place. Around Jerrabomberra Creek to the east of Royalla and to its immediate south several gully control dams and contour banks have been constructed by the New South Wales Soil Conservation Service to minimize the loss of soil and eventually prevent the accumulation of silt in Lake Burley Griffin. PieZd Methods 3 Geological mapping was carried out over a total of 21 weeks during 1973 and 1974. Some previous field work had been carried out by L. Barron, mainly in the Captains Flat area. The information was recorded on aerial photographs and then compiled on to 1:50,000 scale topographic sheets (base supplied by Royal Australian Survey Corps) which were then reduced to the 1:100,000 scale. Some considerable time was spent on aerial photograph interpretation and extensive literature searches. Much of the information provided by these methods was checked by field work. Aerial photographs used were the standard black-and-white 18 cm 1:45,000 scale photos with additional aid ~)rovided by colour 23 cm 1:25,000 scale photos giving coverage mainly of the Australian Capital Territory. Grid references refer to the Michelago 1:100,000 Geological Sheet unless otherwise indicated. CZimate As part of the southeastern tablelands, the Michelago area experiences fairly cool temperatures avera~ing around 18 -22°C (summer) and 5 -8°C (winter), and has an average annual rainfall varying between 550 -750 mm (table 1). This contrasts with the humid cool temperature climate of the nearby South Coast area with its average yearly rainfall of 910 mm. The rainfall is not distinctly seasonal and only moderately variable per annum. {~inds are dominantly from the west, particularly in winter, and are very cold, as they blow off the alpine regions. Light snow generally falls on the ranges; less commonly it occurs throughout the whole area, but is variable and of no great IIuration. Frosts, which are common in winter, impose distinct limits on the growing season. McAlpine and Yapp (1969) considered that the major external climatic control in the area is the north to south alternation of the subtropical belt of high pressure from winter to summer. Vegetation Moisture rather than lithology seems to exert the greatest control on the vegetation pattern of the Michelago area. An extensive study by Story (1969) lists several factors which influence the vegetation distribution pattern. 4 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET TABLE 1 RAINFALL DATA FOR SELECTED LOCALITIES WITHIN THE ~IICHELAGO 1:100,000 SHEET AREA (modified from McAlpine and Yapp 1969, tables 2, 3) Station Latitude Longitude Altitude Mean yearly (m) rainfall (mm) Braidwood 35°24' 149°48' 655 m 713.5 3redbo 36°00' 149°06' 747 m 498.9 Canberra 610 m 595.1 (Acton) Captains Flat 35°35' 149°27' 853 m 727.7 Michelago 35°42' 149°12' 716m 618.2 Queanbeyan 35°18' 149°12' 579 m 595.1 Williamsdale 35°30' 149°12' 792 m 654.1 (Mount Campbell) 1. The dominance in the area of several north - south aligned mountain ridges. 2. The greatest exposure of the northwest slopes to maximum temperatures and the prevailing westerly winds. 3. The severe altitudinal cold along the mountain tops above 1200 m, leading to the sinking of very cold air into valley bottoms and depressions, thus giving rise to two regions of intense winter cold with an intervening warmer region on the slopes. 4. The influence of rainfall and the indirect compli- cations of moist or dry winds, of cold, and of the amount of shelter. Wet, intermediate, and dry sclerophyll forests and savannah woodland were recognized within the New South Wales part of the area by Story (1969) and in the Australian Capital Territory by Woolnough (1939). The wet sclerophyll forest is restricted to the Gourock Range on the eastern margin of the Michelago area, intermediate sclerophyll forest is corrmon on the eastern side of the Tinderry Range,and the dry sclerophyll type is frequently found on the western aspect of the Tinderry Range. The savannah woodland type of vegetation is most common in the Murrumbidgee Valley, with minor pockets located near Captains Flat. Soils I NTRODUCTI ON 5 In a study of the soils of the Queanbeyan - Shoalhaven area, Gunn (1969) nominated six groups of soils present, each further subdivisible into soil families and differentiated according to variations in effective depth, thickness of surface horizons, presence of bleached subsurface horizons, structure, reaction, and colour. The six groups are: 1. Uniform coarse-textured soils, well represented in the central strip of the Michelago area, on granite and Ordovician bedrock. 2. Uniform medium to fine-textured soils, well represented in areas of Ordovician outcrop. 3. Massive earths, found in wetter parts of the Gourock Range, and around l1ichelago and in other sr:"all areas between Bredbo and Royalla. 4. Structured red and brown soils, formed most commonly on Silurian volcanics and sediment bedrock between Bredbo and Royalla. 5. Texture-contrast soils, developed particularly well on granite terrain, for instance, on the Jerangle and Michelago Igneous Complexes. 6. Small areas of alluvial soil, developed most significantly south of Bredbo. This distribution of the soils is complex but the pattern indicates the dominance of uniform-textured, generally shallow soils on mountains; similar soils, but associated with higher proportions of massive earths, on hills; and predominantly massive earths and/or texture-contrast soils in rolling to undulating terrain. More intensive studies on soils in the Michelago area have been carried out by Costin (1954) and Pillans (197P'). Land Use Sheep and cattle grazing is the main form of land usage, with the latter being more common in areas of higher rainfall. Merino sheep and Shorthorn and Hereford cattle are the major breeds represented. Small pockets of dairying and pig raising are scattered throughout the region, the former venture becoming increasingly less pro~itable to operate. Small quantities of fodder crops, for example, lucerne, oats, hay, and turnips, are grown on the arable areas. The land with gentler topography is fairly rich in comparison with the rugged, higher areas dominated by Ordovician 6 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET rocks and has consequently been cleared to a greater extent. Various pasture improvement methods are practised in the area, from the simplest and oldest method of the removal of trees by ringbarking to the now most commonly used method of topdressing the natural pastures with fertilizers such as superphosphate by means of light aircraft. The granites between Michelago and Jerangle, with the exception of the Tinderry Granite, generally form lOW-lying areas and are heavily weathered; these areas require the liberal application of superphosphate to enrich them. A minor degree of timber getting takes place to the south and east of Captains Flat, with a timber mill located to the north of the township. Quarrying and rr.ining activities are dealt with in the appropriate sections. Previous Literature Since the first recorded geological observations of Clarke in 1852, a wealth of knowledge of varying accuracy has been accumulated on differing geological aspects of the area of the Michelago 1:100,000 sheet. Work with a dominantly economic or physiographic bias was carried out at a fairly early stage. Contributions to physiographic knowledge were made by Clarke (1860), Andrews (1905,1910, and 1934), Sussmilch (1910), Craft (1933), Legge (1937), Woolnough (1939) (the last two more particularly within the Australian Capital Territory), Costin (1954), and Jennings (1972). Economic geology studies of a general nature include the published articles of Carne (1908), Baker (1915), Carne and Jones (1919), Fisher (1947a, b), McLeod (1965), and Gilligan (in prep.). Detailed studies more particularly concentrated on the Captains Flat area. The orebody of the now abandoned Lake George mine at Captains Flat was discovered in 1874 and, particularly in post- depression years, attracted a great deal of geological analysis, starting with Maclaren's (1928) L,rivate report to the company and including significant subsequent studies by Kenny and Mulholland (1939, 1940, 1941), Tyler (1947), Edwards (1943) and later Edwards and Baker (1953), Glasson (1952), the staff of Lake George Mines Pty Ltd (1953), Sedmik (1965), and Oldershaw (1965). A more detailed economic bibliography can be found in Gilligan (in prep.). Studies of a more generalized geological character were begun as early as 1914 with Browne's studies near Cooma, followed by Browne (1931, 1944, 1947) and Joplin (1942, 1943, 1945), Veevers (1952, 1953b), Hancock (1963), Scheibner (1974a, b), Strusz (1971), and Crook et al. (1973). INTRODUCTION The last two works are particularly significant for their regional correlations, while the \vork of Scheibner has been heavily drawn on for the structural and tectonic analyses. Information of variable usefulness has also been gained from numerous exploration company reports submitted to the New South Wales Department of Mines, ur.published field reports by geology students of the Australian National University, and several unpublished theses. The theses (figure 2) contain information relevant to a high proportion of the area and include Brown (1928), Sharp (1949), Williamson (1949), Tyler (1949), Lyon (1949), Veevers (1951), Glasson (1957), Snelling (1957), Richards (1967), Nisbet (1970), Baczynski (1970), Joyce (1970a), Slepecki (1973), and Pillans (1974). Useful theses in neighbouring areas are those of Phillips (1952), Johnson (1964), and Stauffer (1964) . Maps covering the Michelago 1:100,000 sheet area are the Canberra 1:250~000 Geological Sheet 1st and 2nd editions, of Joplin et al. (1953) and Best et al. (1964) respectively, Brunker et al. (1971), Pogson (1972), Scheibner (1974b), and Gilligan (1974a). Much information has been gleaned from the neighbouring Tantangara and Braidwood 1:100,000 Geological Sheets of Owen et al. (1974a) and Felton and Huleatt (1975, 1977) respectively, and the Canberra 1:50,000 Geological Sheet of Strusz and Henderson (1971). A regional airborne survey of the Canberra 1:250,000 sheet area has been flown by the Bureau of Mineral Resources Australia. Flying was at 1680 m above sea level and only aeromagnetic data were recorded. Flight lines were flown east-west at a spacing of 1.5 km. A magnetic contour map of 1:250,000 scale has been produced for the area but was unavailable for use at the time of compilation of the Michelago 1:100,000 Geological Sheet. Petrographic descriptions were provided by Dr L.M. Barron and palaeontological determinations by L. Sherwin and Dr J. Pickett. Physiography The topography of the Michelago area shows some variety, a reflection of its location in a complex part of the Southern Highlands of New South Wales (figure 3). Strusz (1971) subdivided the area into three physiographic regions -- the Cotter Horst, the Murrumbidgee Valley, and the Tinderry-Gourock Highlands -- and considered them to be mainly structurally controlled. The Cotter Horst is located along the western side of the Michelago area and is bounded on its eastern margin by the Murrumbidgee River lying adjacent to a steep scarp. It consists of high peaks and narrow ridges generally trending in a northerly direction, with the highest peak being Mount Clear of 1603 m. The ranges form the catchment area for the Naas and Gudgenby R[vers; the former flows parallel to the resistant ridges along zones of weakness; the latter (as noted by Craft 1933) is marked by a linear course, clean angular junctions, and restriction to well-defined fissures. 7 8 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET 10509 1949 NISBET 1970 RICHARDS 1967 0--0 --t-o\='\-:;:: TYLER 1949 LYON 1949 GLASSON 1957 ~.--. i iI WILLIAMSON I i i . 0--0--0 i i t-- 11"-----""111 SLEPECKI 1973 o \~BROWN mB o ~ BACZYNSKIJ 1970 I iPILLANS\ 1974 SNELLING JOYCE 1970a Figure 2. Thesis areas on the Miche1ago 1:100,000 sheet o, 1, 2, em 3, 4, 5, INTRODUCTION 9 5 H SCALE o 5 Kilometres 10 Figure 3. Sketch map showing physiographic units and cultural features on the Miche1ago 1:100,000 sheet o, 1, 2, em 3, 4, 5, 10 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The Murrumbidgee Valley is a fairly narrow physiographic unit with a meridional orientation between the villages of Bredbo and Tharwa. With an average altitude between 700 and 1000 m, the valley consists of an alternation of ridges and small depressions through which flow tributaries of the Murrumbidgee River, for example, the Micaligo and Gungoandra Creeks. In general the Murrumbidgee Valley is some 150 m higher than the Canberra Plains to the north. The eastern scarp of the Cotter Horst, rising some 100 m from the river, bounds the valley on its western side, while to the east the boundary is more gradual, ascending to the Tinderry Range. The Tinderry - Gourock Highlands consist of the Tinderry Range (1618 m at its highest point), developing eastward into the topographically more significant Gourock Range separating Jerangle and Captains Flat from Krawarree (Araluen 1:100,000 sheet). Towards the northern end of the area, the Molonglo River develops a narrow valley forming a wedge in this generally high-altitude region. Characteristically a meridional orientation still dominates the highlands, with the two ranges striking north .- south. The major rivers, the Queanbeyan and the Molonglo Rivers, have a fair northerly component and the minor streams are similarly aligned. Southeast of Jerangle the topography is less rugged, with altitudes around 1200 m -- a reflection of the different nature of the rocks. The Bredbo River flows westward along the southern margin of the area and, like the Queanbeyan River, presents a minutely branching system of tributaries, each small tributary flowing in a distinctive valley of its own. Craft (1933) related this type of stream pattern to high ridge or terraced country which the multitude of streams cannot reduce efficiently. These river systems contrast with the mature system of the Murrumbidgee River which has integrated its tributaries into a few large, evenly spaced branches. Jennings (1972), in an analysis of the Canberra landforms, postulated recent formation for the region, refuting Opik's (1958) idea that the landforms were the unexhumed survivals from Bowning faulting and mid-Devonian volcanicity. Fault lines, such as those of the Murrumbidgee, Queanbeyan, and Narongo Faults,' are often expressed as scarps which have been taken as boundaries for the physiographic regions. In general, large horizontal displacements have taken place along these fault lines and, as Jennings (1972, p. 373) noted, "the survival of Palaeozoic fault scarps which nearly coincide with the fault-lines themselves is not compatible with the elimination of big dislocations of relief of the same age. Such contrasts are consonant with differential erosion of fault-line scarps, and renewed movement along old fault-lines". The Molonglo River cuts across the Tinderry - Gourock Highlands, forming in part V-shaped valleys which cut into the older surface, and elsewhere broad gentle valleys as part of that surface. The Molonglo River is therefore thought to be antecedent in character. INTRODUCTION In a broader study of the Monaro region, Costin (1954) noted four recognizable erosion surfaces, i.e., pre-Oligocene, Oligo-Miocene, Pliocene, and post-Kosciusko, with the Oligo- Miocene and Pliocene surfaces still well preserved on surfaces below 1000 m. The formation of the rift valley between Cooma and Tharwa is considered to be a post-Kosciusko event. Future Work Because of the regional nature and small scale of the mapping, it is obvious that many problems have arisen which cannot be fully answered at present. More detailed mapping, with closer examination of certain aspects, is certainly warranted. For instance, geochemical work would permit a much better analysis and subdivision of the various volcanic formations. Age dating and detailed petrographic analyses of the granites could be useful, as would more detailed and comprehensive structural analyses. 11 GEOLOGICAL SETTING The Michelago 1:100,000 sheet area belongs to the southern portion of the Lachlan Fold Belt. forms part of the Tasman Fold Belt System, and its traced back to the Cambrian Period (figure 6). structurally This fold belt origins can be Three main structural zones are recognized within the area (figure 7). These are the Cowra - Yass Synclinorial Zone, the Captains Flat - Goulburn Synclinorial Zone, and the Molong - South Coast Anticlinorial Zone. The Cowra - Yass Synclinorial Zone is represented by the Canberra Synclinorium, the Captains Flat - Goulburn Synclinorial Zone in part by the Captains Flat Synclinorium, and the Molong - South Coast Anticlinorial Zone by the Cotter, Cullarin, and Rocky Pic Anticlinoria. Late Ordovician rocks are the oldest represented in the area (table 4). They are found within all three subdivisions of the Molong - South Coast Anticlinorial Zone and are represented by the Adaminaby Beds in the Cotter Anticlinorium and by the Foxlow Beds in the Cullarin and Rocky Pic Anticlinoria. The Adaminaby Beds are poorly fossiliferous proximal flysch sediments, highly deformed but of generally low metamorphic grade. They crop out along the western margin of the Michelago area. By comparison, the quartz-rich distal flysch sequence of the Foxlow Beds is far more extensive and shows the same level of deformation and metamorphism. Graptolites are characteristically found in these deep-water sediments but are usually restricted to dark-grey or black slate and chert bands (appendix 1). Within the Cullarin Anticlinorium, Early Silurian (Late Llandoverian) proximalflyschsediments of the Ryrie Formation crop out between Bredbo and Michelago in a narrow belt. A basal siltstone member is termed the Gungoandra Siltstone Member. Above the basal siltstone, the formation is dominated by thick quartzite units with minor siltstone/shale interbeds. The whole unit is characterized by facies changes and a lesser degree of deformation and metamorphism in comparison with the unconformably unGerlying Foxlow Beds. Fossils, consisting of graptolites and possible lamellibranchs, are relatively scarce, and to date, have only been found in the lower silty units of the Ryrie Formation. Sediments and volcanics of Middle to Late Silurian age are restricted to two structural zones, the Canberra and Captains Flat Synclinoria. Within the latter, the Hoskinstown Group comprises several formations, commencing with the Copper Creek Shale. This dominantly siltstone formation has a basal quartzite, the Rutledge Quartzite Member. The Co~per Creek Shale is overlain by the Kohinoor Volcanics. Both of these formations crop out between Hoskinstown and the Bredbo River. To the northwest of Captains Flat, along Primrose Valley, a sequence of Silurian sediments with minor tuffsis thought to be part of the Copper Creek Shale. However, \IUII\I IIIIUIIIUIII IIIII IIII! IIUI IIIII lUll 1111\ UII lUI 0004941750 14 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET extensive deformation and faulting of the unit inhibits any conclusion on the rock's affinities. North of the Michelago 1:100,000 sheet boundary the Carwoola Formation overlies the Kohinoor Volcanics but southward it thins out, permitting the uppermost formation in the Hoskinstown Group, the Captains Flat Formation, to overlap conformably on to the Kohinoor Volcanics. The Captains Flat Formation extends from just south of Captains Flat to north of Hoskinstown. Two members (the Yandyguinula Member and the Sinclair Conglomerate Member) have been differentiated within the formation. Fossils, generally brachiopods and corals, have been collected within the group, mainly from the Copper Creek Shale and the Captains Flat Formation (appendix 1). The Hoskinstown Group has been folded into a northwards plunging synclinorium with the synclinal closure exposed south of Captains Flat. Minor outliers of Late Silurian volcanics and sediments appear sporadically on the downthrown eastern side of the Narongo Fault between "Norongo" and the Bredbo River. These appear to represent minor centres of volcanic eruption, although no vents have been located. The Cowra - Yass Synclinorial Zone, which has narrowed to an average width of some 8 km, is represented in the Michelago area by the Cappanana Formation, the Col±nton and Williamsdale Volcanics, and the Bransby Beds (table 2). As in the case of the Hoskinstown Group, the succession begins with marine sediments (the Cappanana Formation), including numerous limestone lenses, which are overlain in an interfingering and conformable fashion by the Colinton Volcanics. The volcanics are characterized by numerous facies changes, both within the succession and along their strike length. North of Michelago the Colinton Volcanics give way to the massive, more persistent ash flow tuffs of the Williamsdale Volcanics, which broaden in outcrop area towards the north. The Bransby Beds are a mixed unit of volcanics and marine sediments which interfinger with the underlying Colinton Volcanics. They are the uppermost member of the succession and extend along the eastern margin of the Murrumbidgee Batholith. The Bransby Beds range in age from Late Silurian to Early Devonian, the latter age limit being suggested by fossils in lacustrine sediments east of Tharwa (appendix 1). An elongated body of intrusive dacitic porphyry parallel to the Murrumbidgee River between Colinton and Michelago (the Livingstone Porphyry) and other minor intrusive porphyries (Cosgrove, Bullanamang, and others) are scattered throughout the Bredbo -Royalla belt (photo 6). Emplacement of granites has been extensive within the anticlinoria. The most significant mass is the Murrumbidgee Batholith which has intruded the Adaminaby Beds in the Cotter Anticlinorium adjacent to the Canberra Synclinorium. It is separated from the Late Silurian sediments by the Murrumbidgee Fault. The Murrumbidgee Batholith has been subdivided into some eleven bodies (emending Joyce 1973b), six of which are located partly or wholly GEOLOGICAL SETTING within the Michelago area. These are the Murrumbucka Tonalite, the Clear Range and Callemondah Granodiorites, the Shannons Flat and Tharwa Adamellites, and the Booroomba Leucogranite, plus numerous minor unnamed leucogranites. The. Murrumbidgee Ba~holith is a. composite batholith containing ma~nly S-type gran~tes (as def~ned by Chappell and White 1974) (table 7). Within the Cullarin Anticlinorium, the granite masses are of smaller areal extent and represent both the I-type and S-type of Chappell and White (1974). These granitic bodies include the Michelago and Sapling Flat Igneous Complexes, theTindeLry, Urialla, Watch Box, and Harrisons Peak Granites, and the Good Good and Bredbo River Adamellite~ plus numerous minor unnamed acidic intrusions (table 7), including unnamed porphyries. Conforming more distinctly to the classic I-type, the Jerangle Igneous Complex and Boro Granite along the eastern side of the sheet are actually part of the extensive Bega Batholith. This batholith intrudes the Rocky Pic Anticlinorium. Gravels of possible Permian age may be the youngest Palaeozoic rocks cropping out within the area of the Michelago sheet. These are found mainly in the vicinity of Captains Flat. The Whinstone Basalt crops out near Jerangle and is the product of the Tertiary basaltic volcanism which prevailed throughout the Southern Highlands. Minor basic necks and several dyke swarms, intruding both granites and sediments, are of possible Tertiary age. West of "Norongo",around GR 170450, numerous granite porphyry dykes which intrude the Ordovician metasediments are probably related in age to the major granite intrusions. 15 Undifferentiated Cainozoic sediments are generally of limited extent but are distributed throughout the area. Unconsolidated sediments of Quaternary age are restricted to the vicinity of the Murrumbidgee and Queanbeyan Rivers. Four episodes of deformation are recognized in the period from the Ordovician to the Devonian. These are characterized by major erosional breaks, differences in structural style, and faulting. More recent faulting movements have been the major controlling factor in the development of the present topography (figure 7). Correlations have been maue between units of the Canberra and Captains Flat Synclinoria in the sheet area (table 2) and between these units and formations in the southeast region of New South Wales (table 3). 16 LOCAL GEOLOGY OF THE MICHELAGO 1:100,000 SHEET STRATIGRAPHIC TABLE COWRA - YASS SYNCLINORIAL THARWA LONDON BRIDGE MICHElAGO STRUSZ RICHARDSON STRUSZ RICHARDSON RICHARDSON 1971 This paper 1971 This paper This paper DEVONIAN Welded-- de lien ite tuff r--'--1-\iG Shale. sandstone Bransby Beds 1--1--'- Pridolian Goosoon Beds ~'''''''"FV Bransby B/Yarralumla F I-A;id-::anics ---?--?f-'--'-- Colinton Volcanics ------f------ Colinton Volcanics Wi II iamsdale ~sdale ------ Volcanics Volcanics Ludlovian L'"d"~7f------~~m Colinton Colinton Volcanics Volcan ics F--F-« Cappanana Fm ?--?- z -e a: ;:) -I III Wenlockian llandoverian 2 GEOLOGICAL SETTING CORRE LATIONS 17 ZONE CAPTAINS FLAT SYNCLINORIAL ZONE BREDBO CAPTAINS FLAT PRIMROSEVALLEY STRUSZ RICHARDSON STRUSZ HULEATT RICHARDSON RICHARDSON 1971 This paper 1971 1971 This paper This paper - f--?--?- 1 1CaPtains~ I--?--?- Formation ~t-I--Carwoolar-----.---- Bransby Carwoola Fm Goosoon Be:/ Beds Captains Flat Beds Formation 1-1_1J I-----". Kohinoor Colinton carwo~ Volcanics Volcanics Beds Kohinoor '5..-_"'-:.- -- Colinton Koh inoor Volcanics I\-cappanana Beds Volcanics "-- Vol~ics \~ Copper Creek -?--?-- "-- Shale Copper Creek.. Cappanana Fm Copper Creek ~--p- f- ShaleShale -?- ?- f-=?t2 - Copper Rutledge RutledgeQuartzite QuaruiteCreek V V V V MemberShale Member ~~"""'-' Ryrie ~----Formationf----.- RutledgeGungoandra Si Its tone Member Quartzite ~~"""'" o, 1, 2, em 3, 4, 5, 18 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET REGIONAL TAB L E STRATIGRAPHIC COWRA - YASS SYNCLINORIAL WEST EAST Tantangara Canberra Quidong West East Owen et al. 1974. C,ook et al. 1973 (after Link 1970) Crook et al. 1973 Crook et al. 1973 z ... Z 0 > w 0 -- c ,~ :g ;t PRIOOLIAN NOT RECOGNIZEO BlueW~e Beds - City Hill Shale 'Guidong limestone Fairbairn Riverside Formation "-Ii ~Formation 0 '; III 0 .. :;; § ..j ~ .. ~ "----- j.. E St Johns J:.::i Chutch c Beds ~ .. Cam Hiit-f-- ~'8 San1stoneV ii ... z Ii ~ ... Q. iii: ~ Goobarra,andra:::l Bed. ..I jj;;; ~ Peppercorn Black MountainSandstone P1.errianla~hBed. Silt.ton.' ~ Tom"!'ngState Circle -1~?-Shale Ii 'i > 0 -1--1-... Ii Tantang.,.::::i Bed. ---1---1- '--f-- ~1-1 - ,1- Unnamed ~ Ii Nunl.' Beds Action Shale 1 phyllite.:~ Nung.,0 Bed. Pl'obably p,e.ent Member:; 0 .t depth 0 ;S~1 1-co or: ~0 ..I Pittman Formation 3 CORRELATIONS GEOLOGICAL SETTING 19 ZONE CAPTAINS FLAT -GOULBURN EAST SYNCLINORIAL ZONE Yass Michelago Captains Flat Braidwood Pogson and Baker 1974 Crook et al. 1973 Herein Herein Felton and Huleatt 1977 Sinclair Conglomerate ----- --~~-1-....1 -- rovan--c;e.1i -lSilerang- ... ~ '> Formation Formation8 /17"II Captains Flat'Do Cowridge Bransby Formationi Siltstone Beds II BombayIi ... a~~~~ua~ VolcanicsIII 8 " ~Booroo Rosebank Shale e to Woodlawn TUlgeranong / ! '; VolcanicsPonds Black Bog Shale ...lirouo Tuff Member / ~ " Long Flat ~~ ... Silverdale Formation 0 Kohinoor I Volcanics~~j :z: VolcanicsColinton -j :z: Laidlaw Formation Voicanici II .:l,~ Copper Creek Oe Drack Willow Bridge Tuff i 3 Shale Formation De Drack Cappana"a ="0 Itl FormationYa.. Sub -Group Formation :=> I... ----- ~ -1il Douro 'Series' --- - Sandlills" ------ Rutledgei Hawkins Volcanics Hawkins 'Series' Quartzite CreekMember LimestoneQ Member <. Bango Limestone Mundoonen Sandstone Ryrie Formation Gunloandr. Si Itltone Member _F__F_ - -#-- Birkenburn Bed. Merigan Black Shale Jerrawa FOllow FOllow Bed. Bed. Beds Birkenburn Beds ORDOVICIAN TO EARLY DEVONIAN STRATIGRAPHY The stratigraphy of the Michelago 1:100,000 area is summarized in table 4. ORDOVICIAN The Ordovician rocks of the Michelago 1:100,000 sheet area are present in two major north - south-trending belts. In the west, a narrow belt of metasediments is bounded by the Clear Range Granodiorite to the east and the Shannons Flat Adamellite and Callemondah Granodiorite on the western side. The western boundary relationship is shown on the Tantangara 1:100,000 Geological Sheet (Owen et al. 1974a). This belt of Ordovician rocks is assigned to the Adaminaby Beds as it is deemed to be an extension of Ordovician sediments mapped by Adamson (1955) in the vicinity of Adaminaby. The central and eastern portion of the Michelago sheet area is dominated by a wide belt of flysch-type metasediments into which numerous granitic bodies have been intruded. The western boundary of the belt is formed by a narrow zone of Silurian acid tuffs and sediments extending along the entire length, while the Ordovician sediments are framed along the eastern edge by a smaller belt of Silurian rocks cropping out in the northeast corner, and by the western side of the Bega Batholith. The Narongo Fault roughly subdivides the belt into two sections, and also marks the boundary between the Cullarin and Rocky Pic Anticlinoria. This large flysch body has been termed the Foxlow Beds. Cotter Anticlinorium ADAMINABY BEDS (Sa) Fairbridge 1953 after C.L. Adamson Derivation The Adaminaby Beds are named after the township of old Adaminaby (GR 535101, Berridale 1:100,000) which lies to the west of Bredbo. Distribution As described by Adamson (1955), the Adaminaby Beds are part of a belt of Late Ordovician sediments which extend from victoria through to the Australian Capital Territory. As an extension of the main body of the Adaminaby Beds (Owen et al. 1974a), a narrow septum of metasediments continues northward into the central area of the Murrumbidgee Batholith, between the Shannons Flat Adamellite and the Clear Range Granodiorite, and it is the eastern side of this belt which lies within the area of the Michelago 1:100,000 sheet. The belt has an average width of 3 km from its northern extremity near "Orroral" homestead (GR 774538, Tantangara 1:100,000) to south of the Callemondah Granodiorite where it widens to over 10 km. 1111111111111111111111111111111111111111111111111111111II111 D004941760 22 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Synonymy and Previous Work Adamson (1955) described a sequence of Late Ordovician quartzites and slates in the vicinity of old Adaminaby. He noted (p. 80) that "the widespread occurrence of Upper Ordovician graptolites indicates a continuity of these sediments from the eastern boundary of the map [Adaminaby Mili tary I-mile sheet] to as far west as Nimmo Trig. Station", Le., 149 0 00 to 148 0 36' E. Fairbridge (1953) noted shales containing graptolites of Eastonian and early Bolindian age in the Adaminaby area. He named the shales the Adaminaby Beds and considered that they were probably correlatable with the Nungar Beds and presumably conformable above the Kiandra Beds. Description The metasediments of the western belt consist predominantly of siltstones, with minor interbedded sandy sediments increasing in frequency eastwards. They have been converted into grey phylli tes and brown slates by regional metamorphism, and develop eastwards into brown mica schists with recrystallized fine-grained quartz sandstones rich in chlorite and muscovite. Some small outcrops of blue-black shales were also noted by the author. As a consequence of the intrusion of the Murrumbidgee Batholith, a thermal metamorphic aureole of quartz hornfels has developed, varying from l~ km to about 100 m in width. Within this zone, Joyce (1973b, p. 180) noted the presence of biotite and a "less schistose recrystallized texture within slate, phyllite and recrystallized sandstone which elsewhere contain abundant schistose chlorite and muscovite". As a result of the recrystallized texture, it is fairly resistant to weathering (appendix 2-1). Apart from minor indications of bedding, no sedimentary structures have been observed. Alternating bands (maximum width 3 mm) of finer and coarser sediments were seen in one specimen collected a few metres from the granite/sediment boundary. Boundary Re~tionships In the Michelago sheet area the Adaminaby Beds are intruded by the Murrumbidgee Batholith. Fauna and Age Poorly preserved graptolites have been collected from fine- grained, cleaved phyllites near the northern extremity of the belt by M. Owen et al. (pers. comm.). They are possibly indicative of a Late Ordovician age. Graptolites of Late Ordovician (Eastonian) age have been noted further to the south by Browne (1931) and Adamson (1955). TABLE 4. STRATIGRAPHY OF THE HICHELAGO 1:100.000 SHEET ERA PERIOD EPOCH ROCK UNIT LITHOLOGY SYHBOL FOSSILS %CKNESS SELECTED REFERENCES ra.:s..i !! Cluaternary Alluvium. colluyium. sand. and gravel Qa Pillan. 1974 u Tertiary Whinstone Basalt Tb 120m Richard. 1967 0 Basalt N Undifferentiated Hill>·le.el gra.el. sand. and Cn Pillan. 19740 z talus breccia Browne 1944:;; u Basic necks n Richard. 1967 Buic dykes / Permian (?) Gravels Pg Olclershaw 1965 Jenngle Towneys Biotite adamellite. ~Ijte. (75 km'l Richard. 1967 leneous Cr..k porphyry. leuco~ite git CompleJ: Adamellite Anembo Biotite -hornblende cranodiorite (DO km 2) Granodiorite gia Minor phases Dominantly leucoeranite gi Boro Granite Hornblende - biotite cranite 10 130 km2 Olcler_haw 1965 Minar ianeou. Acid to intermediate intrusions g Vallance 1966 intrusions V...er_ 1951 U Slepecki 1973 0 Good Good Tounnaline adamellite 0.35 km2 Richard. 1967N "0 Adamellite Slepeck; 1973w c ... Watch Box Biotite cnnite 12 km2 Veeyers 1951c e- ll. Granite Urialla Biotite granite. marginal 17 km2 Veevers 1951 Granite porphyritic adamellite III Tinderry Biotite granite gt 37W Strun 1971 Granite Harrisons Peak Biotite granite II> 3.8 km' Older_haw 1965 Granite Glasson 1957 Brecfbo Ri yer Adamellite I:' 2.5 km2Adamellite Siluro - Devonian Sapling Wanf:\'3h Biotite adamellite. porphyry. 17 km 2 Richard. 1967 Flat Igneous Adamellite minor biotite -homblende g'w Slepeck; 1973 Late l~~~jan Complex adamelliteDanswell Biotite - hornblende 8 km 2 Richard. 1967 N'evDnian Creek granodiorite gsd Granoc:I iori te o ~ ~ H () H ~ Z Ul >-3 ~ >-3 H G'l ~ :c 0< l\J W u o N o W .. ..J .. ... Late Silurian MichelalO Hookellan Biotite granodiorite gan 3.1 km2 Brown 1918 to Early Igneous Granodiorite Deyonian Complex Onslow Biotite -hornblende 1.1 km' Joplin el ,I, 1953 Granodiorite rranodiorite gco Siluro - Micaligo Biolite (hornblende) 35 kfnl strusz 1971Adamellite adamellite gcc Devonian Koolamb>h Biotite - hornblende 26 km2 Adamellite adamellite gck Minor Leucogranite. aplite. and phases biotite adamellite gc Porphyry gcp Minor Quaru - feldspar and quartz- SoD oorDhyries feldsoar - biotite porohyrY Cosgroye Porphyry S-Do I km2 Pillan. 1974 Porphyry Liyingstone Dacitic porphyry S-DI 19.5 km2 Sharp 1949 Porphyry Bullanamang Dacitic porphyry S-Du 0.4 km2 Browne 1944 Porphyry Joplin 1943 Bransby Rhyolitic tuff. minor sediments S-Db Br.chiopods 1100 m Joplin 1943 Beds Si ltstone and sandstone s-Dbs Limestone S-Dbi Late Siturian Williamsdale Rhyodacitic tuff S. 4330 m(?) Sharp 1949 (Ludloyian) Volca:nics Minor rhyolitic intrusions Swm Colinton Rhyolitic to myodacitic tuff and sy Br.chiopod. 4000m Best et.1. 1964 Volcanics minor sediments undifferentiated Hancock 1963 Tuggeranong Tuff Member s.t Minor sediments -siltstone. S.. shale, sandstone, limestone Rhyolitic lithic crystal tuff S.r Pumiceous lithic tuff s.p Lithic tuff Syl White to aeam-coloured crystal tuff S.c Fine.gra.ined ash tuff S•• Rhyodacitic to dacitic lithic S.d crystal luff Cappanan. Shale. siltstone. mudstone Sp Brachiopod. 700m Best et.1. 1964 Formation Limestone Spl Hancock 1963Silurian Tuff and minor sediments Spt '"ol:> Gl t'l o 8 ~ ~ :f t'l :s: H R t'l ~ o I-' I-' o o o o o Ul :I: t'l t'l "3 Hoskinstown Captains Flat Shale. tuff. reworked tuff. 51 lI< tv U1 26 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Cullarin and Rocky Pic Anticlinoria FOXLOW BEDS (ef, ef c, efk, ef s) Stauffer et a1. 1964 after w. 01dershaw Derivation Oldershaw (1965) named the Ordovician rocks near Captains Flat but did not cite the origin of the name. Therefore it could be derived from one of three alternative sources: Foxlow Trig. Station (1220 m, GR 177640) to the northwest of Captains Flat, Foxlow Creek which flows north from Foxlow Trig. Station through an area of Ordovician sediments, or the property of "Fo:clo\'l" which lies on the Captains Flat - Hoskinstown road. Distribution Oldershaw (1965) originally named and described the Foxlow Beds in a restricted area close to Captains Flat. However, because of distinct lithological similarities between rocks of this area and sediments in the remainder of the Cullarin and Rocky Pic Anticlinoria, the definition and limits of the Foxlow Beds have been extended to include the latter. The Foxlow Beds crop out over the full length of the Michelago 1:100,000 sheet area in a 30 km wide belt. They are a northerly continuation of the Coolringdonand Binjura Beds described by Joplin (1942, 1943) around Cooma, while within the same belt but much further to the north the Jerrawa Beds have been described near Yass. Synonymy and Previous Work Williamson (1949) described Ordovician rocks several kilometres south of Captains Flat and correlated them with the Binjura and Coolringdon Beds described by Joplin (1942) in the vicinity of Cooma. Glasson (1952 unpubl.) introduced the terms "Beverley Beds" and "Railway Slates" to describe sediments west of Captains Flat. Stauffer et al. (1964) made use of the name Foxlow Beds in anticipation of Oldershaw (1965). While mapping an area 13 km wide by 27 km long between Captains Flat and Hoskinsto~~, Oldershaw (1965) named the Ordovician rocks in this area the Foxlow Beds, with the "Bullongong Shale Member" towards the top of the sequence. Oldershaw's Foxlow Beds and "Bullongong Shale Member" correspond to the "Beverley Be<'ls" and "Railway Slates" respectively of Glasson (1952). However, as Oldershaw's names were published before those of Glasson and Paine (1965), his terminology has precedence. ORDOVICIAN STRATIGRAPHY The term "Bullongong Shale Member" is regarded as invalid under the conditions of the Australian Code of Stratigraphic Nomenclature revised 4th edition (Geological Society of Australia 1973) and therefore only the name Foxlow Beds is retained. Type Area No type area was nominated by either Oldershaw (1965) or Glasson and Paine (1965). However, the Foxlow Beds may be considered to be suitably represented by lithologies in part of the original area mapped by Oldershaw, i.e., west of the Captains Flat Synclinorium, between Captains Flat, Hoskinsto\·m, and the Harrisons Peak Granite. Description The Foxlow Beds contain rock types typical of the quartz-rich greywacke and slate association dominant in much of southern New South Wales. Black shaly beds which have a widespread distribution throughout New South Wales (Sherrard 1954, 1962) have also been noted in the Michelago 1:100,000 sheet area. The beds are a generally low-grade (greenschist facies) regionally metamorphosed distal flysch sequence, consisting of interbedded slates and quartz greywackes, phyllites, dark-grey to black slates, and cherts. Graptolites (appendix 1) are found within black slates and cherts which are present throughout the sequence but are more common towards the top where they also form thicker beds. Coarse sediments, i.e., greywackes/psammites, range in colour from light brown to grey. Some sediments resemble impure quartzites (Williamson 1949), while others are more schistose with higher proportions of argillaceous material in the matrix. Quartz veining is not uncommon and frequently follows the direction of cleavage (appendix 2-2). Along Ryans Creek (GR 110212) the psammites are characterized by an abundance of quartz, well-twinned plagioclase, and minor tourmaline, zircon, and opaque ox~des. Further northwards the rocks are rather fine grained with quartz grains usually less than 1 mm in diameter. Feldspars (0.5mm) are less common and vary from oligoclase to andesine with possible orthoclase. Biotite occurs in aligned flakes around the small augen of quartz and feldspar (~O.l mm). Minor amounts of muscovite, chlorite, apatite, sphene, tourmaline, and iron ore are present. 27 Silicified sandstones (8fs) occur to the east of Primrose Valley. These are thought to belong to the Foxlow Beds, but Oldershaw (1965) included them in his "Rutledge Quartzite". The petrology of a sandstone from GR 152679 is described in appendix 2-3. Finer sediments (i.e., pelites) are developed extensively along Strike-a-Light River and to the south along the Bredbo River. Depending upon the degree of metamorphism, they appear as brown to 28 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET grey slates and grey phyllites. Further westward schist~ and knotted schists (efk) are more common, with andalusite or staurolite retrogressed to sericite agglomerations in most cases. Typically the pelites have a higher percentage of mica (mainly biotite with minor muscovite; appendix 2-4) but less quartz than the psammites. They also have minor chlorite and sericite and numerous fine granules of iron ore. To the west of the Narongo Fault, small outcrops of granulites are present as lens-like bodies of about a metre. in length. The granulites have "a well developed schistosity and are composed of quartz, labradorite, amphibolite, garnet, iron ore, apatite, sphene and a little possible clinozoisite" (Williamson 1949, p. 24). Fine quartz veins are very common throughout the Ordovician sequence. In fairly restricted areas, a contact metamorphism is superimposed on the regional metamorphism (appendix 2-5). One such area is at GR 135321, adjacent to the Sapling Flat Igneous Complex. Here, andalusite crystals (about 10 mm in length) are developed in a greisenized schist (Joplin 1968). The black shales and cherts (efc) are by no means continuous and therefore have limited value as marker beds. - Their lack of continuity is partially a result of displacement of many rock units by large-scale folding and minor faulting, as well as of lateral variations, with black and dark-grey slates ranging into black to grey cherts. They are developed in beds of 15 m maximum thickness in the Captains Flat area, but would appear to be of greater thickness than this to the west. Slates and cherts have been traced south from a quarry (GR 995500) near the Michelago - Burra road, and are sporadically present within a belt extending from the Michelago - Tinderry road (GR 980450) to south of Ryrie Trig. Station (GR 969382) and from near Colinton Trig. Station (GR 980283) to the Bredbo River near "Cappawidgee" homestead (GR 989140). Veevers (1951) indicated small beds encircling the Urialla Granite. Joplin (1945) made extensive examination of black slates from many parts of the State and noted the high percentage (over 75 percent) of silica. Her petrological examinations showed that the "rocks are often banded with finely carbonaceous seams alternating with carbon-free or carbon-poor bands. The non-carbonaceous seams appear to consist of tiny flakes of sericite, small zircons, needles of rutile and occasional tiny grains of quartz in a faintly green almost isotropic base which is not completely resolved. Minute Y-shaped bodies sometimes occur, and these may possibly represent sponge spicules whilst tiny rounded patches of chalcedony are doubtfully interpreted as radiolaria (Joplin 1945, p. 159) (appendix 2-6). ORDOVICIAN STRATIGRAPHY The cherts always have well-developed jointing and sometimes show subconchoidal fracturing. Williamson (1949) identified quartz, sericite, kaolin, and minor iron ore within the cherts, and described carbonaceous bands and small lenses (approximately 0.2 mm long) consisting of slightly coarser quartz with fewer inclusions. Narrow quartz veins are common. According to Oldershaw (1965), the area near Captains Flat originally defined as the Foxlow Beds consists of a sequence divisible into three sections. The lower part is a sequence of alternating greywacke and shale. The beds of greywacke are from 0.3 to 1.8 m thick and decrease upwards in both thickness and frequency. They are dark grey in colour and consist of rounded grains of quartz, feldspa~ and fragments of shale and siltstone 0.5 to 2 mm across, set in a fine-grained matrix of chlorite, biotite, sericite, quartz, and black iron oxide. The well-cleaved interbedded shales range from dark to light grey. The middle section of the Foxlow Beds consists of alternating shale and siltstone with a few thin beds of greywacke. The upper part is mainly shale with a few thin siltstone beds. The shale beds range from dark to light grey and from red to yellow. Some are well cleaved. The beds are mostly from 6 to 30 m thick, but some are as thin as 3 mm. There is some slight metamorphism: many of the quartz grains in the greywacke show marginal intergrowth with the groundmass, and some of the shale beds are extensively sericitized. Oldershaw (1965) considered that the black shale present in the upper part of the Foxlow Beds forms a·distinctive and extensive marker. Between 9 and 61 m thick, the unit consists of graphitic black shale with disseminated pyrite and chalcopyrite. In places it is highly contorted, sheared, and silicified. No current bedding, flute casts, or fossils were found within the Foxlow Beds, excluding the black shale unit which is fossiliferous (appendix 1). Sedimentary structures have not been noted in the cherts and black slates. Within the flysch sequence, sediments appear to be well bedded with variations in bed thickness from a few millimetres to several metres. Graded bedding is more common in the eastern half of the belt, as are ripple marks and sole marks. No current bedding, flute casts, or fossils were found within the Foxlow Beds, excluding the black shale unit which is fossiliferous (appendix 1). Sedimentary structures have not been noted in the cherts and black slates. Boundary ReZationships The boundary between the Foxlow Beds and neighbouring units varies from intrusive to faulted and unconformable. Along their eastern margin, the Foxlow Beds are intruded by the Boro Granite, a part of the Bega Batholith, and throughout the flysch sequence various minor igneous masses have an intrusive 29 30 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET relationship. The Captains Flat Synclinorium is in faulted contact with the Ordovician rocks (i.e., tne Narongo and Ballallaba Faults), but further south towards Jerangle small Silurian outliers overlie them unconformably. In the Primose Valley area the boundary relationships are not clear. The western margin of the Foxlow Beds is partially faulted, as the Burra and Collingwood Faults separate them from the Canberra Synclinorium (figure 7). South of Colinton Trig. Station (GR 980283) the beds are unconformably overlain by the Ryrie Formation and further south by the Cappanana Formation. Fauna and Age Only the black slates and cherts are fossiliferous. They contain graptolites representing various zones within the Eastonian (appendix 1). Some possible late Gisbornian and early Bolindian fossils are also present. As described by Joplin (1945), the graptolites are often very well preserved and appear as black carbonaceous films, as white micaceous films, or as reddish brown films of iron oxide. EARLY SILURIAN Cullarin Anticlinorium RYRIE FORMATION (,Sr, Srg) nov. Derivation The formation is named after Ryrie Trig. Station (958 m) at GR 969382. Distribution Originally one continuous unit, the formation has been displaced by the Collingwood Fault over a distance of some 9 km so that there are now two main areas of outcrop. The northern, more restricted locality lies to the west of Ryrie Trig. Station. The other main area of outcrop exists south of the Collingwood Fault where the unit crops out from Colinton Trig. Station (GR 980283) south to a westward-flowing tributary of Cappanana Creek at GR 983243. Synonymy and Previous Work The Early Silurian rocks in the Michelago area have not been described previously in published literature. However, students of the Australian National University recognized their occurrence during field mapping projects carried out in recent years. '~ney referred to the unit as the "Bedlam Beds" after Bedlam Springs Creek to the south of "Micaligo" homestead. EARLY SILURIAN STRATIGRAPHY Crook et al. (1973) made reference to a quartzite on Colinton Hill to the northeast of Bredbo, regarding it,as a possible proximal flysch sequence of similar age to the State Circle Shale and the Mundoonen Sandstone. Type Section A cross section of the Ryrie Formation is best represented on the east - west ridge of Colinton Hill, the base of the formation at GR 988283 being marked by the Gungoandra Siltstone Member and the top around GR 972283 by massive quartz arenite with minor siltstone/ shale interbeds. Description The lithology of the unit is that of a typical proximal flysch, i.e., interbedded fine-grained and coarse-grained units many metres thick, with distinct lithological boundaries. The Gungoandra Siltstone Member, which is the basal unit of the Ryrie Formation, is overlain by quartz arenite interbedded with minor brown shale and coarse grey sandy siltstone. The fairly massive beds of quartzite become progressively doninant towards the top of the sequence. These white to grey quartzite units are especially well displayed at Colinton Trig. Station. They are highly resistant to weathering and form distinctive knolls and ridges, with the interbedded siltstones forming the saddles. Jointing is a prominent feature of all the quartzite beds but they are totally devoid of sedimentary structures. Quartz is the main constituent, with minor feldspar, muscovite, tourmaline, zircon, and opaques (appendix 2-7). Over a lateral distance of some 5 km of outcrop, only the Gungoandra Siltstone Member is reasonably persistent. Gungoandra Siltstone Member (Srg) nov. Derivation The name of the Gungoandra Siltstone Member is derived from Gungoandra Gap at GR 976245. Type section The type section of the member is present within the type section of the Ryrie Formation on Colinton Hill. Description Characteristically, the Gungoandra Siltstone Member consists of fine-grained yellow-brown to grey-brown siltstone frequently with conchoidal fracturing and ironstaining. It has relatively few sedimentary structures with only a minor amount of crossbedding 31 32 and ripple marking. Thiakness GEOLOGY OF THE MICHELAGO 1:100,000 SHEET At Colinton Hill the Ryrie Formation reaches a maximum thickness of some 1600 m, but it thins quickly to the south. In the northern locality the formation is represented by only a few hundred metres and is dominantly siltstone. The Gungoandra Siltstone Member has a thickness of approximately 150 m near Colinton Hill. Boundary ReZationships The basal siltstone member unconformably overlies isoclinally folded, meridionally trending black-grey slates and cherts of Late Ordovician age -- the Foxlow Beds. The presence of this angular unconformity is obscured by the general mer.idional trend of the adjacent Ordovician sediments. In turn, the Ryrie Formation is truncated by the overlying Cappanana Formation and this boundary appears to be an angular unconformity. Basal quartzites of the Cappanana Formation lie adjacent to the upper quartz arenites of the Ryrie Formation, the boundary being demarcated by periodic gossan outcrops. As a result of weathering and the nature of the topography of the area, the quartz arenites form massive scree slopes, with arenite blocks frequently concealing the boundaries between the arenites and the siltstones. In the northern outcrop area the upper and lower boundaries of the Ryrie Formation are partially masked by alluvium, although fossil evidence is available to prove the existence of the Ryrie Formation and the presence of the Foxlow Beds and the Cappanana Formation. Fauna and Age Although relatively scarce in distribution, a graptolite fauna has been collected from both the northern and southern areas of outcrop. This fauna indicates a Late Llandoverian age (appendix 1). The graptolites are found within the siltstones but are generally confined to very narrow bands as, for example, in the northern area of outcrop, where they are present in a 55 rom thick, soft, weathered, whitish-brown siltstone band. 33MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY MIDDLE SILURIAN TO EARLY DEVONIAN Canberra Synclinorium CAPPANANA FORMATION (Sp, Spl, Spt) after Horner 1973 unpub1. modified from Best et a1. 1964 Derivation The name of the formation is derived from Cappanana Creek which intersects the Bredbo - Jerangle road at GR 998207. When the name was originally introduced by Best et al. (1964) it was misspelt "Cappanama" with subsequent misspelling by Packham (1969) as "Cappanarnrna". Distribution On the l-1ichelago 1: 100,000 sheet the Cappanana Formation extends north from the vicinity of "Cappawidgee" homestead in the south (GR 989140) to Ingelara Creek at GR 971339. It makes a minor appearance north of the Collingwood Fault at GR 960390, but its main area of outcrop in the north centres on the old "London Bridge" homestead at GR 045665, near the Queanbeyan River. The formation is traceable both north of this locality as well as south of the Bredbo River towards Cooma. The meridional strike length of the Cappanana Formation totals some 56 m. The recognized limits of the formation have been extended to include the "London Bridge Formation" of Best et al. (1964). Synonymy and Previous Work The formation was originally included in the "Tinderry Series" by Sharp (1949 unpubl.), but was first referred to as the "Cappanama Beds" by Best et al. (1964) with continuation of the same terminology by Brunker et al. (1971) and Baczynski (1970 unpubl.). Strusz (1971) noted the incorrect spelling and the revised name was pUblished by Pogson (1972). Horner (1973 unpubl.) considered that the "Cappanana Beds" had formation status and this view is held by the present author. Definition of the unit has been extended to include the originally named "London Bridge Limestone" of Veevers (1953a unpubl.) which has since been referred to as the "London Bridge Formation" by Best et al. (1964) and Strusz (1971). Earliest reference to the limestones was made by Mahony and Taylor (1913) who noted that the total width of the limestone near the arch at GR 053678 (photo 1) was some 80 m, including some intercalated shales, with a strike of 15°, dip W65°. Other early workers were Carne and Jones (1919), who were mainly interested in the limestone resources. 11111111111\ 11\1\ 1111\ 111111111I1111111111111111111111111111 0004941761 34 Type Section GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Cappanana Creek, between GR 992186 and GR 982188, is the type area for the formation with excellent lithological representation both to the north and south of the Bredbo - Jerangle road. Basal quartzites pass upwards into dominantly olive to brown mudstones, siltstones, and shales with numerous lenticular limestone bodies and minor sandstones. Minor tuff bands appear towards the top of the sequence. Marine fossils are abundant (appendix 1). Description Shale, siltstone, calcareous siltstone, quartz sandstone, and minor mudstone, limestone, and volcanics are all present within the formation, together with numerous fossil accumulations and a minor amount of mineralization. The limestones (Spl) may be both massive and bedded, although the latter predominate. They are frequently interbedded with narrow bands of siltstone and sandstone. Most of the limestone lenses are small in. size, white to dark grey in colour, and compact to coarsely crystalline in texture. Calcite veins may be present. Fossils found within the limestones include brachiopods, corals, and crinoid stems (appendix 1). Within some of the limestone bands, brachiopods have been distorted by the strong cleavage. Horner (1973) also recorded stressed calcite crystals indicated by curved cleavage. Because of their strong association with other sediments the limestone lenses appear to have been formed in situ, although one exception is a limestone breccia found near "Cappawidgee" homestead (at GR 990145) which may have formed by erosion of a reef and subsequent slumping of limestone blocks into deeper water. Limestones described by Horner (1973) south of the Bredbo- Jerangle road are composed of 5 per cent pellets and 60 per cent calcite crystals, from 1 to 10 mm in diameter, in a matrix of micrite and fine-grained sparite. The limestones also contain an abuncar.ce of crinoid stems distributed evenly throughout the rock with an approximate abundance of 30 per square metre. The sandstones may be ferruginous and fossiliferous, although the fossils tend to be poorly preserved. They are yellowish brown in colour, well rounded and well sorted, consist mainly of quartz crystals with minor feldspar and some muscovite, and may contain clay minerals. The siltstones and other argillites are generally dark brown to grey in colour, may be richly fossiliferous, and are frequently highly cleaved. In proximity to some of the limestone-lenses, the siltstones may contain small (less than 100 mm) elongated pods of fossiliferous limestone. Ripple and sole marks and current bedding are present within the sediments. MIDDLE SIWRIAN TO EARLY DEVONIAN STRATIGRAPHY Sandstones containing minor siltstone bands are dominant at the base of the formation (figure 4). Typical exposures of arenaceous sediments with 100 mm wide grey siltstone bands crop out in the roadcutting at GR 985196 on the Bredbo - Jerangle road and these grade vertically into fossiliferous siltstones with occasional thick siliceous siltstone bands. Argillites with numerous small limestone lenses dominate the central portion of the sequence, but tuffs (Spt) in thin bands make their appearance towards the top of the cappanana Formation. The Colinton Volcanics commence where the tuffs become dominant. In the type area of the formation, a 722-m sequence was measured and found to contain about ten beds of limestone (figure 4). It must be noted, however, that some folding has taken place, although generally this is not readily observable, especially in the tuffs. Therefore it is quite possible that some of the limestone bands are repeated, for example at 470 ffi. photo 1. A view of the London Bridge limestone arch at GR 053678 look~n9 north. The limestone d~ps to the west and is part of the Cappanana Formation 35 111111111111111111~1111111~lllllllllllllllllmm1II1 0004941770 36 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Excluding some special cases, very little metamorphism has taken place. Near the old "London Bridge" homestead, axinite has developed in limestones adjacent to a small intrusion of quartz porphyry. The axinite is present as coarse bladed crystals associated with calcite, epidote, and tremolite (Vallance 1966, Joplin 1968). Thickness Near "Cappawidgee" homestead, the formation is approximately 700 m thick, but the unit becomes much thinner in the vicinity of Michelago. Boundary ReZationships The Cappanana Formation is conformably overlain by the Colinton Volcanics, a thick sequence of predominantly acid volcanics and minor sediments. The boundary is a gradational one, with interdigitation of sediments and tuffs until dominance of the tuffs marks the base of the Colinton Volcanics. Consequently, the Cappanana Formation and Colinton Volcanics boundary indicated on the Michelago 1:100,000 sheet is approximate. Both Early Silurian and Late Ordovician units underlie the Cappanana Formation. An angular unconformity with partial faulting is characteristic of the Foxlow Beds/Cappanana Formation boundary north of the Bredbo River and at London Bridge north of Burra (photo 2). Black cherts and black indurated siltstones and shales are typical of the Foxlow Beds close to their boundary with the Cappanana Formation. At London Bridge a sequence of quartz-rich greywackes and interbedded siltstones and shales displaying crossbedding, minor isoclinal folds, and/or ripple cross lamination, unconformably underlies the formation. The unconformable relationship is suggested by the strong lithological change, indicative of a depositional break, and by evidence for a change in strike of some 30° and in the two units displayed in Burra Creek about 100 m from its junct~on with the Queanbeyan River. North of the Bredbo - Jerangle road, the Early Silurian Ryrie Formation unconformably underlies the Cappanana Formation with the former wedging out towards the south. As quartzites of the two formations come into contact in places, the boundary is sometimes difficult to define. Fauna and Age Fossils, which are prolific within both the argillaceous and the calcareous units (appendix 1), are indicative of a Late Silurian age, i.e., Ludlovian, in contrast to Best et al. 's (1964) earlier postulated Early Silurian age. //111//111/1111111111111111111111111111111111111111111111111 D004941780 FJGURE 4: GEOlOGY OF THE MICHELAGO 1: 100,000 SHEET SI.jh"s" -- tI,,, ...... Str... u' ..- S,It . SIIt.._ ••_.11, ,,_ S"_ . '" " .. ' ~.l!I , . .004 '''*''' I . ...... , IS c. "'dO fa"I, ...." •• _ ",11••• _ C'I t>oI •• _ w,--", • .......11 _.,__• .- ......c,,_ _ . «,..,I ,•••_ I 10'. UofI "', .. OJ.I_• ,~N' _..""•.., ,_.,..,_ "'" ,••_ ...... Sc. ~.. C.I"",,, ,." ..., ....,"".... COLINTON VOLCANICS _ .... Sol,,,•• l._It_ .",1•• 5.10,,_ .~......,......I, ..... fl•• · a _ .1'cMl~ CO" ... Sa.... ,.... - .....~... lI..cdo.. _.,__ ,• ........- J ......,........lao ,,_I, ""MoM ...... h ..... ,•••• ,:;--_ Fe_ Ja _ ~ ----- .0 :-:-:-:-:- 10 ----- ----- , 10 ----- 10 _ " «l -._-_- .. • ~ ---- " ----- " ..~ L ' ,. so ',h" ,. 'C.. l"" ".It. ," ,..I"", """_ C.......•...... ........ ,•• _r...,•.•• .. ----- .. f'C,":~?-'••••'--.i )0 "".' ....... .~ ... ~. .. .. ----- .. ----- " 1O _ .. "k~'d .. ---- " .~ :::,::-\ ,..' ~ L,_.._ Sol"'.... ... .. s'"•• ))s" ,.,. Ol..",c ,.If F ;~•••,.i .. _.cl ... c.I.. ,,,, ,.11 ( ... -' ...."- ."..~ (OLIN TON VOl..C ..... 'Cs.. 1\0"'0 SI :;;---- " -_ S, _~ .... SC••_.JII .._ 10_0_ 0" ..1.1,.. .....t_ ,. IS COl woM " . " " . " :::"v". ~ ::: :- " "v~.,. " ... , -. ...... ...... .' 10 ..... ~ ~ .. ~ ,,'~'~>±';,'~ ........ SCI ./ ,.•-,...-.....,-c1••_ c..... ,.1.." It 5•• 1. _ .1•• 1, d N ----- " 10 _ '" 5,1 ,-.. ..1 _",•••••,. -"0, Sil' ...... S-t,u,1r "-d ... ...._ , Mo _ • .. I> ,oe. C." _.11" 1 .,_ 1...._ Ii · •• hco 1..,_ ... _ ..II il,.,_ .. e ........ .. ---- 90 ----- ,.: ..:, Co",,, _ I.'or 1 " " ---- 1/1 ~ _ .. .. ---- .....,..... ,L__..J ~:;~::~~:':~O~US~LEY.:~It.< ~ ;f l'l :;: H () :x: l'l§:; Gl 0 I-' I-' 0 ? 0 0 0 til :x: l'l l'l t-3 N Royalla Sv Sw Williamsdale 10 Michelago Rhyolitic to rhyodacitic tuff Undifferentiated rhyolitic to rhyodacitic crystal and lithic tuff, minor siltstone. sandstone,and limestone Quartz and pink feldspar crystal tuff Rhyolitic lithic crystal tuff Minor sediments - siltstone, shale. sandstone, and limestone Lithic tuff Pumiceous lithic tuff White to cream crystal tuff Fine-grained ash tuff Rhyodacitic to dacitic lithic crystal tuff Rhyodacitic tuff, massive Siltstone, shale. sandstone, and minor tuff 5 CAL E o 5 S-Db Sv Svt Svr Svs Svl Svp Svc Sva Svd Sw Sp Tuggeranong Member Colinton Svd Bredbo Bransby Beds Colinton Volcanics Wi II iamsdale Volcanics Cappanana Formation Svs Svs --:""7"?1 BASE REFERENCE TOP s .!!..urrumbidgee Fault S-Db~~SV~:::Is~vd=\~~~-I~~~--g Svd Svr~ SiS ~~d\ ~~s~7 - ~ ..:2/ .c ..... Jr---'---svs~ s Sv "'l ..... \Q s:: 11 CD l/l "'tilIII ;><" o CD ..... rt CD 0 00 ::t o El "'.§ rt ::too CD ::t () ~ o ..... I-' ::s ..... \Q ::s rt 11 o CD ::s I-' III <:rto ..... 1-'0 o ::s III 00 ::s ::t .......... O'tl 00 00 tr CD ~ CD CD ::s g. CD <: III 11 ..... o s:: 00 Kilometres 10512 o 1 234 5 I ' I I I ' em MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY not been found in most other thin sections. This unit tends to be more massive in outcrop than the other units, and is the main ridge-former. Fine-grained ash tuff (Sva) This minor unit is developed north of Gungoandra Creek at GR 936268. In outcrop it appears as a yellowish brown fine-grained rock with no obvious phenocrysts (appendix 2-9). Thin section examination reveals small grains of quartz, plagioclase, and alkali feldspar set in a matrix of sericite, chlorite, quartz, zircon, and leucoxene. In the railway cutting to the immediate south of the "Scottdale" railway crossing (GR 939232), very fine-grained greenish brown tuffs are probably part of the same unit. White to aream-aoZoured arystaZ tuff (Svc) This unit is a fairly varied one, with grainsize generally of fine to medium range but with coarse-grained varieties also present, particu 1.arly near Round Hill Trig. Station (GR 944249). On the Bredbo - J«.;rangle road, small lenses of the unit have been mapped and also differentiated in the measured section (figure 4). Here the rock appears to be a siliceous, rhyolitic, lithic, ash tuff. Baczynski (1970) described this unit as a massive, light-coloured, crystal-poor rock. Quartz and feldspar, which are the only phenocrysts, are set in an even, fine-grained, quartzo-feldspathic groundmass. Mafic minerals, other than rare opaques, are generally absent or constitute an insignificant portion of the mode. Some recrystallization has taken place (appendix 2-10). Lithia tuff (Svl) Lithic tuffs are developed most prominently in the northern part of the area, between Michelago and Royalla. North of Michelago the tuffs appear to be composed of minor quartz and feldspar crystals between 1 and 2 mm in size, and numerous lithic fragments of irregular shape and varying in size from 1 to 40 mm. In composition the fragments resemble fossiliferous siltstone, small beds of which are occasionally interbedded with the units. Northwest of Colinton, lithic tuffs crop out in a narrow band. Pumiaeous Zithia tuff (Svp) This particular unit crops out between Bredbo and Colinton in a narrow but fairly distinctive belt. Baczynski (1970) and Pillans (1974) both described portions of this belt, the former identifying pumice fragments up to 250 by 150 mm in length. The fragments are generally extensively flattened with ragged edges, imparting an eutaxitic texture to the rock. In hand specimen the pumice fragments are a dark olive green to black colour. 41 ., GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Rhyolitic croy8tal lithic tuff (Svr) This fairly diverse group is found along the western side of the volcanic belt and extends for most of its length. These rocks contain a high proportion of ash-sized crystal and lithic fragments. Pink K-feldspar and plagioclase are of similar size to the quartz crystals, averaging about 1 rnm in width, and are frequently set in a greenish to bluish groundmass. Biotite may be present but is not essential. Rock fragments, which may constitute up to 35 per cent of the rock (Baczynski 1970), are generally dark in colour. The qroundmass consists of very fine grained, equigranular, quartzo-feldspathic material. The crystal to lithic fragment ratio is variable and the rock can be coarser in some places. Some of the tuffs are welded and have glass shards. although these tend to be masked by the subsequent recrystallization (appendix 2-11; pboto 3). Minor aedimentB (Svs) Minor lenses of sediments are base of the formation. although they the boundary with the Bransby Beds. more prevalent towards the may also be found close to Minor interbeds of limestone, Photo 3. Photomicrograph of a welded rhyolitic crystal tuff in the Colin ton Volcanics (GR 951492). A cage of quartz and alkali feldspar crystal fragments protects triangular shards from compaction and welding. Field of view is 2 x 3 mm. Plane polarized light I[III[IIII~II III [I mIIII [II] 0004941820 MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY sandstone, and tuff appear in the siltstone beds and it is the marine fossils within these water-laid sediments which indicate an age for the formation (appendix 1). Cleav.age is more strongly developed in these sediments than in the tuffaceous units and thus the fossils are frequently distorted. Some very fine-grained sediments occur interbedded with tuffs near GR 934309. Baczynski (1970) described shales from which calcareous fossils had been completely leached out, leaving an external cast of the fossil and giving the shale a pitted appearance. Undifferentiated CoUnton VoZaanias (Sv) The main area of undifferentiated rocks is indicated in the north where the unnamed acid volcanics of Best et al. (1964) have been included with the Coli.nton Volcanics. Most of the rocks appear to be crjstal lithic tuffs of a rhyolitic to rhyodacitic composition, with frequent chloritization of the groundmass. Several small outcrops of breccia flows exist in the Colinton Volcanics and two of these have been shown on the Michelagosheet. Pillans (1974) indicated one such flow at GR 933175, containing angular lithic fragments, often 50 rom in diameter, embedded in finer tuffaceous material. Another breccia at GR 949358 has fragments up to 300 rom in size. Both are probably laharic breccias formed contemporaneously with the major volcanic eruptions. Tuggeranong Tuff Member (Svt) modified from Best et al. 1964 Derivation This tuff member is named after the village of Tuggeranong which is located 9 km north of Royalla and east of the Monaro Highway, on the Canberra 1:100,000 sheet. Distribution The member crops out to the west of the highway near Royalla, and on the Michelago 1:100,000 sheet area is developed east of Rob Roy Trig. Station (GR 915679). It thins to the south and terminates at GR 916629 near Lobbs Hole Creek. Type area Typical outcrop of the Tuggeranong Tuff Member is found at GR 922688. Desaription This unit was formerly mapped as the southern part of the "Tuggeranong Granite" (Best et al. 1964), but recent studies indicate its tuffaceous nature. In outcrop it forms rounded boulders 43 /111///1/11/111111111111111111111111111111111111111111111111 D004941830 44 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET along the summit of the ridge which forms the main topographic feature of its outcrop area. However, this outcrop expression is restricted in extent and it is far more common to find it cropping out in small blocks which form scree deposits, particularly on the sides of gullies. A layering is noticeable, with bands a few centimetres wide varying in their relative proportions of feldspar and quartz. Quartz and pink alkali feldspar crystals with occasional biotite flakes are set in a fine-grained glassy groundmass, which is olive green to grey green in colour in fresh specimens, although a brown groundmass colour appears in specimens cropping out along the top of the ridge. On weathering the groundmass tends to become opaque and greenish white in colour. Quartz and feldspar phenocrysts may be present in equal proportions, but generally the former are dominant; biotite crystals may not be present at all. The groundmass may comprise over 50 per cent of the rock. Phenocrysts are approximately 1 mm in size, although some crystals range up to 3 to 4 mm. Along the margins of the tuff unit some brecciation is developed and small lenses of bomb-rich tuff are also present. At GR 927668, beside a farmtrack, bombs averaging 20 to 50 mm in size are present in a rock comprising 40 per cent quartz phenocrysts, about 5 per cent pink feldspar, and up to 3 per cent biotite. The bombs, which measure up to 120 by 50 mm, make up between 25 and 33 per cent of the rock, have no particular orientation, and are composed of pumice and dacitic(?) rock fragments. The former are characterized by their elongated (3:1 ratio) form and irregular boundaries which form small tongues, and the latter by their approximate spheroidal shape. The size and relationship of the fragments suggest that the source of the tuff, i.e., the vent, is fairly close. Thickness In the vicinity of Bredbo the Colinton Volcanics have a thickness of some 4000 m. Boundary ReLationships The boundary with the underlying Cappanana Formation is a transitional one, with tuffs and sediments interdigitating. It may also be a time-transgressive one within the confines of the Late Silurian, as north - northeast of Michelago tuffs appear right up to the contact with the Late Ordovician Foxlow Beds. Between Colinton and Bredbo the overlying Bransby Beds have a faulted relationship with the volcanics. North of Colinton the boundary is a conformable one marked mainly by a progression from tuff-dominated lithologies into the tuff, siltstone, and very large limestone lenses of the Branby Beds; the moderate shearing of the sediments is due to their proximity to the Murrumbidgee Fault. A faulted boundary relationship is present in MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY the northern part of the area, around Tharwa and Williamsdale. The nature of the relationship of the Colinton Volcanics to the Williamsdale Volcanics is more elusive. It is possible that the two formations are partially time equivalents but formed under differing conditions. It is suggested that the Colinton Volcanics developed in a dominantly marine environment while the Williamsdale Volcanics formed under terrestrial conditions as part of a volcanic Uhigh u . The Colinton Volcanics are intruded at intervals by dacitic porphyries such as the Livingstone Porphyry. Fauna and Age Previous workers in the area (Joplin 1943, Browne 1944) have considered the Colinton Volcanics to be of Late Silurian age, although Best et al. (1964) reverted to a Middle Silurian age. Faunal evidence, collected during the present studies from minor siltstones and limestones of the formation, and the relationships with the Cappanana Formation and the Bransby Beds, strongly support a Late Silurian age (appendix 1). WILLIAMSDALE VOLCANICS (Sw, Swm) nov. Derivation This mass of ashflow tuffs derives its name from the village of Williamsdale, situated on the Monaro Highway at GR 933613. Distribution With the southern extremity at GR 953456, near the township of Michelago, the Williamsdale Volcanics extend northwards for a distance of some 30 km. The northern boundary, which lies on the Canberra 1: 100, 000 sheet, is found near the Queanbeyan - Royalla road. Roughly triangular in shape, the widest part of the mass corresponds with the Williamsdale - Burra road and extends some 5 km. Synonymy and Previous Work Sharp (1949 unpubl.) introduced the name uKeewong - Micaligo Porphyry Complex u, and subdivided the mass into the uKeewong PorphyryU, the uMicaligo porphyryU, and minor acid porphyries. Apart from Young (19 74b unpubl. ), who referred to the volcanics as the uMount Painter PorphyryU, no other nomenclature has been used. Type Area Rhyodacitic crystal tuffs dominate the mass, with typical specimens found to the north of the Williamsdale - Burra road at GR 975616. 45 46 Desoription GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The Williamsdale Volcanics are generally massive in outcrop, typically occurring as jointed, rounded boulders, with the OlooT to 020 0 T joint direction being common. Towards the boundaries of the formation, elongation of the joint blocks becomes more obvious and shearing is present to a greater degree. Mineralogical and textural variations are quite evident within the mass but more detailed field work would be required to subdivide it. Crystal lithic tuffs of rhyodacitic composition showing a mild primary foliation are most common. Rocks do, however, show some variation in the crystal to lithic ratio (compare specimens T26618 and T27154 -- appendix 2-12,2-13) • Included rock fragments may vary in composition between aplites, rhyolites, and pumice to rhyodacites. They range up to 130 mm in length but typically are less than 25 mm, are elongated in a ratio of 3:1, and have a horizontal attitude. In the type area, large, relatively unweathered boulders of the ashflow tuff contain sporadic rock fragments up to 80 mm long and 20 to 30 rom wide. Generally, howeve4 the rock fragments are a comparable size to the crystals. Quartz is an important constituent, I-mm size crystals making up to 25 per cent of the rocks. In crystal tuffs, quartz crystals may range up to 5 mm in size, for example at GR 975625 (appendix 2-12). Feldspars form up to15 per cent of the tuffs on the average. The plagioclase (5 per cent) ranges in composition between Anzo and An30 and alkali feldspar (10 per cent) is sometimes present as sanidine. The average crystal size range is 0.3 to 1 mm. Biotites (5 -10 per cent, 0.5 to 1 mm) mostly show alteration to chlorite, epidote, leucoxene, and other minerals, which together produce the characteristic blue-green colour of the tuffs. While crystals and lithic fragments have a typical grainsize of 0.3 to 1 rom, the matrix, which frequently shows signs of recrystallization, averages around 0.008 mm in grainsize. Glassy blebs have been found in one specimen, but glass shards appear to be absent. However, welding has possibly taken place in some of the tuffs. Alteration has occurred in all the rhyodacitic tuffs, with biotite and feldspar showing the greatest degree of alteration. Minor amounts of a more acid rock are present within the Williamsdale Volcanics (Swm) but their exact nature and relationship to the rhyodacitictuffsare uncertain. Thin section study suggests that they could be either lavas or shallow intrusions. Most are rhyolitic in composition and range from coarse porphyries with crystals up to 7 mm, to fine-grained, seemingly layered rocks. A good example of these rock types was found near a small roadside quarry on the Williamsdale -Burra road, at GR 978603. MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY A specimen from here is dominated by quartz, sanidine, and plagioclase (oligoclase/andesine) (appendix 2-14). Other such rocks may be found at GR 003672, GR 975530, and GR 996585, cropping out as small dyke-like bodies or small lenses. Weathering and alteration have taken place and are particularly obvious in the coarser varieties. Included with the rhyolitic porphyries are microadamellite porphyries, for example, in the previously mentioned roadside quarry on the Williamsdale - Burra road and at GR 983576 near Burra Trig. Station. Crystals of feldspar may range from 7 rom to 1 rom in size. Although textures suggest a shallow intrusive nature, the possibility of an extrusive origin cannot be discounted. Another porphyry of granitic composition crops out near Burra Trig. Station. Restricted in outcrop, it is a coarse-grained rock (pink euhedral feldspars and quartz crystals up to 15 rom) containing rock fragments up to 120 rom in length. Thiokness In the Michelago 1:100,000 sheet area some 85 km 2 are covered by the Williamsdale Volcanics. However, the thickness of the formation is difficult to calculate. The sequence west of Keewong Trig. Station (GR 005573) strikes north - south and dips west at 55°, and if this attitude is maintained throughout the body a thickness of some 4330 m could be developed. Boundary Relationships The Williamsdale Volcanics have an intertonguing relationship with the Colinton Volcanics, the latter lying both stratigraphically above and below the former. The southern extremity of the Williamsdale Volcanics tongue crops out just south of Michelago. It would appear that the volcanics were formed in Late Silurian times, probably contemporaneously with the Colinton Volcanics, and more than likely under terrestrial conditions, thus giving rise to a large, comparatively massive unit intertonguing with lithologically varied submarine units. As part of the eastern margin of the Williamsdale Volcanics coincides with the BurraFault, shearing is a characteristic feature of the margin. For example, a specimen from GR 008572 near Keewong Trig. Station has a well-defined foliation that wraps around the phenocrysts, a feature not so evident in specimens collected from localities further to the west. Along the southeastern boundary, the volcanics are more massive in outcrop and therefore easily distinguishable from the cleaved sediments and tuffs of the Colinton Volcanics. 47 48 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Cleavage is developed more readily along much of the western boundary of the volcanics and in places this poses difficulties in distinguishing between the Williamsdale and Colinton Volcanics. Age A Late Silurian age is postulated for the formation because of its stratigraphic relationship with a recognized Late Silurian formatio~ viz. the Colinton Volcanics. BRANSBY BEDS (S-Db, S-Dbl, S-Dbs) Joplin 1943 Derivation The Parish of Bransby in the County of Beresford is both the type area and the source of the name for the Bransby Beds, originally defined by Joplin (1943). Distribution The Bransby Beds extend the length of the Michelago 1;100,000 sheet, from Tharwa to south of Bredbo. Mapping further to the south has failed to differentiate the Bransby Beds from the underlying Colinton Volcanics. Synonymy and Previous Work Joplin (1943) originally introduced the name Bransby Beds to describe an acid volcanic/tuff and sedimentary rock sequence thought by her to be of Ordovician age, overlying the Coolringdon Beds of known Ordovician age, and overlain by an "Upper Silurian" sequence. Following on from Joplin's work, Sharp (1949 unpubl.) described the Murrumbidgee limestone and slate sequence on the Murrumbidgee River further north near Michelago and mentioned that it was correlatable in part with the Bransby Beds. He disagreed with Joplin's hypothesis of an Ordovician age for the beds, as he considered them to be of Silurian age. SUbsequent literature has referred to them as the "Goosoon Beds", the term first introduced by Best et al. (1964) and used without question until Strusz (1971) queried the name's validity. Best et al. (1964) indicated a type area at the junction of Goosoon Creek with the Murrumbidgee River (at GR 929517), northwest of Michelago. Hancock (1963 unpubl.) considered the beds east of Tharwa to be of Early Devonian age, basing his conclusion on fossil data, lithological features, and the stratigraphic position, but neglected to name the beds. Walpole (1964) briefly noted an exposure of "Upper Devonian" freshwater sediments lying unconformably on Silurian volcanics at Tharwa. Best et al. (1964) merely indicated the existence of "Lower Devonian" shale and coarse sandstone, while Strusz (1971) MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY extended the concept of the Devonian to include welded dellenite tuff overlying shale and sandstone. Type Area As originally defined by Joplin (1943), the Bransby Beds consist largely of volcanic and pyroclastic material, although pelites are occasionally present. Thinly bedded limestones alternate with tuffs near the base, and lenses of limestone occur near the top of the sequence. The type area is found in the Parish of Bransby which lies to the northwest of Bredbo, between the Murrumbidgee River and Gungoandra Creek. Desoription The Bransby Beds consist of rhyolitic tuffs (S-Db), limestone (S-Dbl), and minor shales and sandstones (S-Dbs). Limestones crop out sporadically along the whole strike length. Near the base of the unit, narrow seams of limestone only a few centimetres in width arE interbedded with tuffs, but occasionally larger lenticular masses occur. Joplin (1943) noted that some of the marbles towards the top of the sequence exhibit evidence of both dynamic and contact metamorphism; for example, limestones north of "Bumbalong" homestead (GR 923294) demonstrate well-pronounced contact phenomena, with aggregates of tremolite, diopside, sphene, plagioclase, and sporadically a little biotite present in nodules, or a mosaic of calcite and dolomite. The silicate minerals tend to give the rock an augen structure. Joplin (1943) thought the rocks to originally have been dolomitic limestones with argillaceous impurities. Limestones have also been described by Joplin from Cotters crossing on the Murrumbidgee River (at GR 928415) and from west of Gungoandra Creek. In the former locality the recrystallized limestone is fairly even grained (about 0.1 rom) and contains strained calcite twin lamellae; in the latter locality, small limestone lenses lie within a shear zone and consequently have been recrystallized into marbles by dynamic metamorphism. The lenses contain elongated porphyroblasts of calcite up to 2.5 nun long and lenticular aggregates of smaller calcite grains surrounded by somewhat elongated grains exhibiting secondary twinning with curved lamellae. One of the largest limestones bodies is composed of white to grey recrystallized limestone. It crops out north of "Bumbalong" homestead at GR 918313 and has been folded adjacent to the Clear Range Granodiorite. Most of the limestones crop out in a distinct linear horizon along the Murrumbidgee River (photo 4). AS noted by Joplin (1943), pelites are generally restricted to a horizon just above, and sometimes interbedded with, limestones and tuffs near the base of the Bransby Beds. They are predominantly buff coloured with a slight sheen. In thin sections 49 so GEOLOGY OF THE MICHELAGO 1:100,000 SHEET photo 4. Sheared limestone and tuff units Murrumbidgee Fault and MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY 51 .~~~~~~~~~~ ."~~~~~~~.~~~~"~::~~_~~,-:.~.J Sh;'Bred IImeston~~~"'~' -,- Strike 017'dip vertical • . ~ ';J:' ~ ~~~ - . -~--:....-- In -.~..........~ >- Tulia '. --.:....,;:...-~.=,....-.-~~~~<-,- ., " . .c cleavage 020 :f1 dip W steeply ~\/?-..~ .,1!-- ~~ ~..., GI -'':: ,2 -g t----~:::- ---------__ c ~-----------i(II ~ Cl of the Bransby Beds lying adjacent to the Clear Range Granodiorite at GR 925550 1111111111111111111111111111111111111111111111111111111I1111 D004941850 52 GEOLOGY Of THE MICHELAGO 1:100,000 SHEET they are found to consist of a scaly aggregate, the only recognizable constituents of which are chlorite, sericite, and quartz, together with a little carbonaceous and chalcedonic material, the latter forming pressure shadows around limonitized pyrite crystals. More definite phyllites have been noted. TO the south of Tharwa, approximately west of Williamsdale and the Murrumbidgee River, bedded sediments are developed more prolifically, but they lack the typical limestone lenses. The sediments, with their neighbouring rhyolitic tuffs, are bounded by two arms of the Murrumbidgee Fault, and consequently show shearing and deformation, for example, at GR 898620 where widespread kinkinq is present. Siliceous shales, siltstones, and less common sandstones are developed with minor interbedded tuffaceous sediments (photo 5). Photo 5. Bedding and angular tuff fragments in tuffaceous sediments of the aransby Beds at CR 933464 mlllllllllll[llI~1111111/ [I~ 0004941860 MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY Rhyolitic tuffs and rhyolites(?) eXhibiting varying degrees of shearing and metamorphism are developed extensively along the line of outcrop (appendix 2-15). Joplin (1943) described a relatively unaltered type from south of Gungoandra Creek, close to the Murrumbidgee River, as containing phenocrysts of quartz and orthoclase and occasional crystals of plagioclase in a felsitic groundmass, the phenocrysts varying from 0.3 to 2 rom in size. The quartz crystals are idiomorphic, somewhat corroded, with undulose extinction. Orthoclase crystals often have sericitized cores and show fine polysynthetic twinning caused by strain, The groundmass probably consists of an aggregate of quartz and feldspar. The more highly altered volcanics show stretching of quartz crystals, the disappearance of orthoclase, the partial replacement of biotite, and the replacement of the fluidal fabric of the groundmass by a well-marked schistosity. The tuffs display all gradations from an igneous rock to a crystal tuff. In some cases, (for example, at GR 913202; appendix 2-16) shearing has so destroyed textures in the rocks that it is difficult to decide whether the rock was originally a volcanic arkosic sediment or a crystal tuff. Silicification and epidotization also affect many of the rocks. On ~he northeastern side of the Murrumbidgee River, near Tharwa, brackish water shales with abundant Lingulella, fish bones, and Psilophyton (appendix 1-117) (Hancock 1963) alternate with coarse sandstone with well-rounded unimodal grains. The shale and sandstone members are up to 18 m thick and the whole sequence dips east at 030 o -035°T. The shales break into equant blocks and show very little cleavage or distortion of original bedding. Rhyolitic tuffs both underlie and overlie the sediments and they appear to be similar in composition to the tuffs of the Bransby Beds to the south. Another narrower band of sandstone and shale crops out to the west of the main sediment band but this dips to the ~orthwest. As a result of the close relationship between the tuffs and sediments, this area of outcrop has been regarded by the author as part of the Bransby Beds. Thickness A thickness of 2100 m was suggested by ~ancock (1963) in the vicinity of Bredbo. Further north, near Michelago, the succession is interrupted by faulting and porphyry intrusions (photo 6). Boundary Relationships The relationship between the Colinton Volcanics and the overlying Bransby Beds is difficult to determine, as the degree of deformation of the Bransby Beds is one of the few distinguishing features. Proximity to the Murrumbidgee Batholith could account for the difference in deformation, so the Bransby Beds are perhaps 53 111111111111111111111111111111111111111111111111111111111111 0004941870 54 GEOLOGY OF' THE MIOIELAGO 1: 100. 000 SHEET Photo 6. An intrusive contact between the Livingstone Porphyry and southward-dipping tuffs of the Bransby Beds at GR 936528 (contact to left of hammer) only a continuation of the Colin ton Volcanics. South of Bredbo, Pillans (1974) considered the tuffs close to the Murrumbidgee River to be the sheared equivalent of the Colinton Volcanics. Here they are strongly cleaved and/or sheared, with many beds containing prominent quartz phenocrysts up to 5 rom in diameter. He also noted sporadic lenses of shale or sandstone. An alternate theory suggests that the Bransby Beds are the western equivalents of the Cappanana Formation (Baczynski 1970). Baczynski proposed the existence of a major syncline on the basis of similarities of the tuff and sedimentary sequences on both sides of the volcanic belt. 1[11 n1111111 11I111111[11 [III 0004941880 MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY Near Bredbo, Colinton, and Tharwa the relationship between the Colinton Volcanics and the Bransby Beds would appear to be a faulted one, but in the vicinity of Michelago the boundary is gradational with the dominantly tuff lithology of the Colinton Volcanics giving way to the sediments and tuffs of the Bransby Beds to the west. Because of the degree of deformation, facing is impossible to determine and the beds could be facing either upward or downward. Along their western margin the Bransby Beds are faulted against the Murrumbidgee Batholith. They are also intruded by the Bullanamang and Livingstone Porpllyries and by minor unnamed porphyries. Fauna and Age Fossils collected from the sedimentary units indicate a Late Silurian age, with deposition possibly continuing into earliest Devonian time, as suggested east-southeast of Tharwa (appendix 1). Captains Flat Synclinorium HOSKINSTOWN GROUP Stauffer et al. 1964 after W. 01dershaw Named .after the township of Hoskinstown at GR 225775 on the Canberra 1:100,000 sheet, the group consists of the Copper Creek Shale, KohinoorVolcanics, Carwoola Formation, and Captains Flat Formation. Stauffer et al. (1964) used the name in anticipation of Oldershaw (1965) and noted that the group was of Silurian age, resting unconformably on the Late Ordovician Foxlow Beds. The "Captains Flat Group", a name proposed by Glasson and Paine (1965) to embrace the "Copper Creek Beds", Kohinoor Volcanics, and "Captains Flat Beds", is thereby invalidated by previous publication of the term Hoskinstown Group. The formations within the group extend from south of the Bredbo River to near Bungendore (Canberra 1:100,000 sheet), a distance of some 80 km. They form the Captains Flat Synclinorium, with small outliers appearing along the line of the Narongo Fault, from "Norongo" to the Bredbo River. The base of the Hoskinstown Group is marked by a basal conglomerate and sandstone, followed by a succession of marine sediments, volcanics, and pyroclastics, while the top of the group is mostly obscured by alluvial deposits. The sequence is of Silurian age, with most of the beds being Late Silurian. 55 //11///1/1//11///11///1/1/1/1///1/11///11//1//1/1///11///11/ D004941890 56 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET COPPER CREEK SHALE (SC, Scr, ScI, Sct) Best et al. 1964 Derivation Copper Creek, a small creek trending northeast through Captains Flat at GR 206584, is the source of the name for the Copper Creek Shale. Distribution The Copper Creek Shale crops out along both limbs of the Captains Flat Synclinorium, with the best exposures in road and rail cuttings north of the mine workings on the western limb. The formation forms the southernmost outcrop of the synclinorium, and minor isolated outcrops are present along the line of the Narongo Fault, near "Norongo" (GR 180458), Anembo (GR 150368), and north of Jerangle (GR 134289). Another area of outcrop is in Primrose Valley, approximately 12.5 km northwest from Captains Flat. Synonymy and Previous Work The term "Copper Creek Beds" was first introduced by Glasson (1957 unpubl.) for the basal Silurian sediments in the vicinity of Captains Flat. This name remained in usage by some authors (Glasson and Paine 1965, Packham 1969) in spite of the publication of the name Copper Creek Shale by Best et al. (1964) and others. Type Area With the exception of the minor limestone lenses, the best exposure of the formation is in Copper Creek, near the Captains Flat Railway Station (GR 207586). Desoription As described by Oldershaw (1965) the formation is a sequence of thin-bedded grey and black shale, argillaceous siltstone, and thin beds of tuff, with the underlying "Rutledge Quartzite" given separate formation status. However, in agre~nent with Glasson (1957), Glasson and Paine (1965), and Huleatt (1971), the author considers the "Rutledge Quartzite" to be the basal member of the Copper Creek Shale. Above the basal quartzite member, the remainder of the formation is dominated by shales with minor limestone lenses (ScI) and tuffs (Sct). The shales contain thin lenses, small pods, and disseminated crystals of pyrite and chalcopyrite. Small lenses of limestone, less than 30 m thick and 150 m long, are present near the middle of the formation and these are associated MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY with more calcareous shales and tuffaceous sandstones. The limestone at GR 213625 is heavily altered and recrystallized, while a limestone further north at GR 215672 is sufficiently intact to reveal fossils of definite Silurian age, possibly Wenlockian (appendix 1). Limestone lenses are also found at "Norongo", west of Anembo, and in Primrose Valley. The first two have been described by Baker (1915), Carne and Jones (1919), and Williamson (1949). Glasson (1957) also mentioned a persistent tuffaceous shale band containing crinoids and other fossils. The band is best seen in drill core from DDH S.A. 993, drilled by Lake George Mines pty Ltd at Captains Flat. Glasson and Paine (1965) described marked facies changes along the strike, from shale to tuffaceous shale and from calcareous shale to limestone. To the northwest of Captains Flat, field mapping has revealed the presence of a sequence of phyllites, black silicified shales, feldspathic sandstones, silicified sandstones, and minor tuff and limestone lenses in a zone along Primrose Valley (GR 130670) • The whole area is highly faulted, with a strongly developed slaty cleavage. From Rutledge Trig. Station (GR 167702,Canberra 1:100,000), the beds trend southwest and then adopt a north - south strike, which may be tracp.d for some 9 km. In particular, one tuff band may be traced from GR 125649 to GR 129615 over 3.5 km. A fault traceable along Primrose Valley separates the tuffs, feldspathic sandstones, limestones, and phyllites from the eastern area of black shales and sandstones. Silicified sandstones are prominent further eastward. Although no fossils were found in these units, probably because of the extensive shearing and splintering, lithological correlations suggest that these rocks are part of the Copper Creek Shale. The Rutledge Quartzite Member is thought to be represented by minor sandstone bands along the eastern margin rather than by the silicified sandstones further east (shown as efs); the latter are thought to be part of the Ordovician sequence. Previous workers (Best et al. 1964) correlated a portion of this sequence with the "Carwoola Beds". RutZedge Quartzite Member (Scr) Best et a1. 1964 Derivation The name is derived from Rutledge Trig. Station (996 m) at GR 167702 on the Canberra 1:100,000 sheet. Distribution The member crops out sporadically on both limbs of the synclinorium and to the southwest of Hoskinstown. An area mapped as "Rutledge Quartzite" by Older shaw (1965) to the east of Primrose Valley, and traceable south from Rutledge Trig. Station, would 57 58 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET appear in fact to be a silicified sandstone of the Foxlow Beds and has been shown as such on the map. The petrology of a sandstone from GR 152679, similar to the one south of Rutledge Trig. Statio~ is described in the appendix (ap~endix 2-3). Synonymy and previous work Older shaw (1965) introduced the name. "Rutledge Quartzite" as a separate formation name, although Stauffer et al. (1964) had previously published the name in anticipation of Oldershaw. Type area The best exposure of the Rutledge Quartzite Member is near Grose Meadow Trig. Station (GR 204723 on the Canberra 1:100,000 sheet). Desoription Glasson and Paine (1965) believed the Rutledge Quartzite Member to be either a fault breccia or a sheared agglomerate, noting that in places the rock resembles a perfect conglomerate with rounded quartz pebbles in a siliceous matrix, while elsewhere it has a large number of quartz fragments which resemble injections into a fault breccia zone on which there has been further movement subsequent to the quartz emplacement. A third type, wherein the bed closely resembles a sheared agglomerate of dacitic composition, could mean that volcanism occurred from the start of Silurian deposition. As noted by Oldersha~! (1965), the Rutledge Quartzite Member consists of beds of white quartzite and conglomeratic quartzite, 0.6 to 1.8 m thick, interbedded with thin siltstone. The conglomeratic quartzite contains rounded cobbles up to 150 rom across, of white quartzite, silicified black slate, and silicified grey slate, all of which were probably derived locally from the Late Ordovician sequence. The quartzite is composed of poorly sorted rounded grains of quartz set in a sparse fine-grained silicified matrix, with many of the quartz grains having sutured margins and irregular outlines; the latter features suggest that the grains have been partly resorbed and metamorphosed. Very few bedding planes and no current or graded bedding were noted. The quartzite has been tightly folded, extensively sheared, and invaded by veins of white quartz from 50 to 150 rom wide. In addition, some of the cobbles in the conglomerate have been elongated parallel to the minor folds. In places the quartzite contains disseminated cubes and irregular masses of pyrite up to 6 rom across. During the folding of the Captains Flat Synclinorium, the Rutledge Quartzite Member was broken up into numerous sheared lenses, ranging from 45 to 460 m long and from 1 to 90 m thick. The quartzite crops out as narrow rocky ridges and forms a useful marker bed. MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY Thickness The Copper Creek Shale would appear to range from 60 to 150 m in thickness, with the basal Rutledge Quartzite Member varying from 1 to 90 m. Boundary ReZationships The Rutledge Quartzite Member rests unconformably on the Late Ordovician Foxlow Beds. It is overlain by the remainder of the Copper Creek Shale which in turn is conformably overlain by the Kohinoor Volcanics. The gradation from the tuffaceous shales of the Copper Creek Shale to the coarse porphyritic rocks of the Kohinoor Volcanics suggests a slow change in environmental conditions. Along the line of the Narongo Fault the Copper Creek Shale tends to be covered by alluvium and therefore crops out poorly. Fauna and Age Except for the few minor limestone lenses, the Copper Creek Shale is generally unfossiliferous in character. Fossils indicative of a Silurian age have been collected from north of Captains Flat at GR 215672 (appendix 1). KOHINOOR VOLCANICS (Sk) Lake George Mines Pty Ltd 1953 Derivation The volcanics were named after Kohinoor Trig. Station (GR 212587), the location of the Kohinoor mine. The northernmost shaft of the mine intersects Elliots gossan on the ridge immediately west of Captains Flat. Distribution In outcrop the volcanics occur on both limbs of the Captains Flat Synclinorium, extending northward from l~ km west of Jingera Trig. Station (GR 210492) for some 45 km to Bungendore (Canberra 1:100,000 sheet). South of Captains Flat, sporadic outliers of Kohinoor Volcanics appear along the Narongo Fault at "Norongo" and west of Anembo, with a continuous band of volcanics present from just north of Jerangle to south of the Bredbo River. Synonymy and Previous Work Glasson (1957 unpubl.) has given a detailed account of significant geological reports on Captains Flat and its surroundings, listing Maclaren (1928 unpubl.), Kenny and Mulholland (1939, 1940, 1941), W.H. Tyler (1947 unpubl.), E.W.J. Tyler (1949 unpubl.), Lyon (1949 unpubl.), the staff of Lake George Mines Pty Ltd (1953), Edwards (1943), and Edwards and Baker (1953), the last two dealing 59 60 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET more specifically with the mineralization. Lyon (1949 unpubl.) introduced the terms "Kohinoor Tuffs" and "Eastern Massive Fragmentals" to describe the western and eastern limbs respectively of the synclinorium's volcanic sequence, and, along with Williamson (1949 unpubl.), was one of the first to fully recognize the interbedded nature of the lavas and tuffs. Previous workers had believed the porphyritic rocks to be intrusive. Glasson (1957 unpubl.) recognized the synclinal nature of the Silurian sediments, and his work was elaborated on by Glasson and Paine (1965), Oldershaw (1965), Strusz (1971), and Davis (1975). Glasson (1957 unpubl.) introduced the name "Kohinoor Volcanics Group", and Lake George Mines Pty Ltd (1953) published the terms "Kohinoor Volcanic Group" (p. 912) and Kohinoor Volcanics (p. 911). Stauffer et al. (1964) and Best et al. (1964) used the term Kohinoor Volcanics. Descriptions of the formation were published by Oldershaw (1965) and Glasson and Paine (1965). Type Area As the Kohinoor Volcanics have been best described in the vicinity of the mine shafts at Captains Flat, this may be considered to be the type area for the formation. Detailed mapping has been carried out around and throughout the mine workings, predominantly by Lyon (1949), Glasson (1957), Glasson and Paine (1965), Nisbet (1970), and Davis (1975). Desoription Considerable work has been carried out by geologists of the Electrolytic Zinc Co. of A/asia Ltd (Davis 1974) who recognized the significant part played by facies changes, lensing of units, and the resultant interdigitation of extrusives and pyroclastics. The rock types include crystal, crystal lithic, and lapilli tuffs (appendix 2-17), agglomerates (volcanic breccias), rhyolitic lavas (appendix 2-18), shales and other fine-grained rocks, volcanic cherts, and sinters (developed primarily in crystal tuffs of the mine area). L.W. Davis (pers. comm.) defined three dominant facies, all of which show considerable interdigitation. He also invoked different vent sources for the bulk of the material within each facies. The three facies are the Baldwins dacitic facies, the Kohinoor rhyodacitic - dacitic facies, and the Ballallaba andesitic facies. The Ballallaba andesitic facies is present only in the northern part of the eastern limb of the Captains Flat Synclinorium, near Ballallaba Creek (GR 242630) after which the facies is named. Rock types consist of andesitic to leucoandesitic crystal and lithic tuffs and probably some lavas. The andesitic varieties thin southward and disappear south of Tigercat Creek (GR 230595). To the west, the Ballallaba facies would appear to MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY interdigitate with the Kohinoor rhyodacitic to dacitic facies. The Kohinoor rhyodacitic to dacitic facies is named after Kohinoor Trig. Station and is best developed on the western limb of the synclinorium. Its base is marked by a zone of dacitic tuff and fine-grained tuff, which in turn is superseded by highly siliceous pyritic rhyolitic crystal tuffs. Sinter development is widespread throughout the rhyolitic tuff zone, indicative of shallow-water conditions, while a well-defined volcanic vent is represented by agglomeratic structures at GR 210534 and GR208528. Volcanic cherts are developed north of this vent. The Baldwins dacitic facies, named after Mount Baldwin at GR 208527, is a rather monotonous suite of dacitic-rhyolitic crystal tuffs, with rhyolitic lavas developing near the top and representing a higher degree of acidity in the effused magma and possibly shallow-water to subaerial conditions. The Baldwins dacitic facies in part overlies the other facies and there is also some evidence for minor interdigitation between the Baldwins and Kohinoor facies. Within the Kohinoor Volcanics, crystal tuffs with compositions ranging from rhyolites to andesites, are dominant. The phenocrysts are almost entirely feldspar or quartz, although rare mafics have been observed; the phenocryst content of the tuffs varies from 3 to 60 per cent. Quartz is commonly between 2 and 4 mm in size with some greater than 10 mm, but feldspars rarely exceed 2 to 3 mm. The microcrystalline groundmass is usually homogeneous. Small lithic fragments have been noted but any such fragmental texture is generally well obscured by processes of deformation. The andesitic crystal tuffs and lavas are best exposed just north of Tigercat Creek (GR 230595) on the eastern side of the synclinorium. Dacitic rocks are most widespread and are well represented elsewhere (appendix 2-17). Rhyolitic tuffs, which are scarcer than either the dacitic or andesitic varieties, crop out in only two known localities; near the Lake George mine area, extending from a point 800 m north in a southward direction for over 3500 m, with a thickness of some 75 m; and in the Golf Course -Bollards area (GR 218536), extending over some 2.5 km. It is thought that some alkaline rhyolitic varieties also occur, as evidenced by a distinctive marker unit with numerous closely packed large phenocrysts of quartz and microcline; this unit can be traced for about 3.5 km in the vicinity of the Lake George mine. L.W. Davis (pers. comm.) disagreed with Oldershaw's (1965) conclusion that agglomerate is the most abundant rock type in the Kohinoor Volcanics; Davis did realize, however, that characteristic agglomeratic textures may be concealed in outcrop, partially by weathering, and may also have been partially or completely destroyed by later events. Agglomerates are well exposed 61 62 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET at Mount Baldwin and in a road cutting 0.8 km north of the Lake George mine workings. Fragments vary in size from a few millmetres up to several metres, with those less than a metre most common. They are usually ovoid to elongate, but can be rounded, angular to subangular, and irregular, with the last shape least common. Spindle shapes are rare. The fragments consist of crystal tuff enclosed in a crystal tuff matrix. The agglomerate fragments have fine-grained outer rims, only a few millimetres in thickness, attributable either to chilling against the medium, or alteration by the medium, in which the bodies have been dispersed. L.W. Davis (pers. comm.) suggested that the rounded outlines of the fragments could reflect their origin as volcanic bombs or could indicate that they formed in a churning-pebble dyke. primary flattening accentuated by stretching is probably responsible for the elongate shape, shown by analysis to have commonly a long axis:short axis ratio of 2:1 to 5:1. . Rhyolitic lavas, which are of minor importance volumetrically, are frequently closely associated with cherts and quartzites. The rhyolites are best exposed south of the mine area where relatively short and thin units of siliceous rock up to 30 m thick and, at most, 100 to 200 m long are found. These lenses may form zones traceable over several hundred metres. The colour ranges from white and off-white, through buff and pink, to brown. The grainsize varies from fine to cherty. Thin sections reveal flow banding and phenocrysts of quartz and K-feldspar in a highly siliceous feldspathic groundmass (appendix 2-18). The matrix usually exhibits a mosaic texture which may be due to the 9ivitrification of glassy material. Subsequent aeformation has resulted in numerous irregular sericitized fractures. Accessory zircon and leucoxene may be present. Fine-grained rocks include airfall tuffs, reworked tuffs, and purely sedimentary material. The tuffs are almost completely reconstituted. They display no sedimentary structures and only sporadically a few phenocrysts. Fine tuffaceous horizons may be the lateral equivalents of coarse tuffaceous fractions. The shale lenses are of major economic importance despite their relative scarcity within the formation. The most significant lenses are the Keatings Shale Member (not indicated on map) which is 6 m to 12 m thick, and the Elliots Shale Member (not indicated on map). Both of these are best developed in the vicinity of the mine workings. Close to the Elliots gossan, i.e., at Kohinoor Trig. Station (GR 212587), and for 500 m north of the lode outcrop, the shale horizon is dominantly silty shale or siltstone and in hand specimen the rocks are grey coloured, splintery to fissile in habit, with no mineralogical details visible. The silt-size fraction is variable and there is a complete gradation from rocks with 10 per cent silt to true siltstones which have only 5 to 30 per cent clayey material. The original fine material is now represented by chlorite or sericite - muscovite. MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY There is evidence both for a true water laid origin for the shales and for volcanic influences. Many fine-grained rocks are found to contain tiny phenocrysts (mainly quartz) only a fraction of a millimetre across. Others are siliceous, with a composition of finely mixed quartz and sericite. Barite has been recognized, frequently accompanying quartz in veins but sometimes as a mineral within the rock itself. Sinters are developed within the rhyolitic crystal tuffs in the mine area. They are randed or layered rocks with bands up to 15 mm thick, have a cherty appearance, and consist of a fine admixture of silica and sericite. Close parallelism of the layers possibly denotes a primary sedimentary origin. Individual layers can be traced for a few metres but these usually terminate and sometimes branch or join. Xenocrysts can be seen between and within the layers. Individual layers are separated by partings of crystal tuff of similar thickness. Iron-pearing cherts or jasper, attaining thicknesses of 5 to 10 mover lengths of a few hundred metres, appear near the upper contact of the Kohinoor Volcanics. The cherts occur as pods and lenses mainly on the eastern limb of the synclinorium (e.g., at 800 m north of the Lake George mine workings) or as irregular bodies in agglomerates, filling the gaps between fragments and partially surrounding fragments (for example, on the eastern bank of the Molonglo River, some 600 m north of the Molonglo River road bridge at Captains Flat, minor isolated chert fragments and agglomerates occur with a matrix of tiny lithic fragments containing magnetite). The chert is variegated in grey and red-brown colours. It is massive with a conchoidal fracture and weakly to strongly magnetic. Frequently the rock is travsered by quartz "gash" veins. Petrologically, fine-grained (0.03 to 0.25 mm maximum) quartz with mosaic texture accounts for well over 95 per cent of the chert, with 5 per cent composed of epidote, white mica, and opaques. Barite is also found sporadically. Minor outliers of the Kohinoor Volcanics between the Bredbo River and "Norongo" appear to be dominantly andesitic in composition (appendix 2-20, 21) with rhyolitic rocks less common (appendix 2-19). Generally all tuffs are strongly chloritized. Thickness Oldershaw (1965) estimated a thickness of some 760 m for the Kohinoor Volcanics but failed to indicate where this thickness occurred. In many places it is doubtful whether such a thickness would be attained, e.g., on the eastern limb of the synclinorium. Boundary Relationships The Kohinoor Volcanics appear to rest conformably on the Copper Creek Shale, as shown in the area of the mine workings. In turn the volcanics underlie the Captains Flat Formation near . 63 64 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Captains Flat, either conformably or paraconformably, and underlie the Carwoola Formation conformably as evidenced near Carwoola Trig. Station (Canberra 1:100,000 sheet). Age No fossils have been collected from the Kohinoor Volcanics so that its age may only be deduced from its stratigraphic position. A middle to late Ludlovian age is postulated, in agreement with Huleatt (1971) who correlated the Kohinoor Volcanics with similar lithologies at Braidwood. CARWOOLA FORMATION (Sa) modified from Best et a1. 1964 Derivation The formation is named after Carwoola Trig. Station at GR 193766 on the Canberra 1:100,000 sheet. Distribution The Carwoola Formation crops out over an area of 26 km 2 in the vicinity of Carwoola Trig. Station, 3 km west of Hoskinstown, and extends southward along Primrose Valley to the north of the Michelago sheet area. It can also be traced south to "Foxlow" homestead (GR 212700 on the Canberra 1:100,000 sheet) and north to Bungendore. The Carwoola Formation is not exposed in outcrop in the Michelago sheet area and therefore has not been indicated on the map, but it is possible that some portion of the formation may exist below the Captains Flat Formation. Synonymy and Previous Work Formerly referred to as the "Carwoola Beds u in all published literature, the unit is now given formation status as there would appear to be sufficient knowledge of the upper and lower boundary relationships. The name was first published by Best et al. (1964) and Stauffer et al. (1964), and the unit was first described by Oldershaw (1965). Type Area The type area is in the vicinity of Carwoola Trig. Station where Oldershaw (1965) recorded good exposures of the formation. Here it appears to rest directly and conformably on the Kohinoor Volcanics. Desoription As described by Oldershaw (1965), the formation consists of over 1200 m of well-cleaved brown shale, grey siltstone, and rhythmically bedded argillaceous brown sandstone. The sandstones MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY appear in rhythmically interbedded groups, separated by 100 to 150 m of shale. Within each group of sandstones the sandstone beds increase in thickness from 50 mm at the bottom of the group to 1 m in the middle and decrease to 50 mm at the top. Graded bedding is found in the sandstones. No volcanics are present. Thickness Oldershaw (1965) measured a sequence over 1200 m thick, probably in the vicinity of Carwoola Trig. Station. Boundary ReLationships Near Carwoola Trig. Station the Carwoola Formation appears to rest directly and conformably on the Kohinoor Volcanics, and north of Hoskinstown it conformably underlies the Captains Flat Formation. It pinches out to the south in the region of "Foxlow" homestead, leaving the Captains Flat Formation directly overlying the Kohinoor Volcanics. Age No fossils have been collected from the Carwoola Formation but, because of its relationship with the Kohinoor Volcanics and the Captains Flat Formation, a Late Silurian age may be postulated. CAPTAINS FLAT FORMATION (Sf, Sfs, Sfy) Best et a1. 1964 modified from Gibbons 1962 Derivation This formation is named after the township of Captains Flat at GR 215585, and crops out in its vicinity. Distribution As indicated by Best et al. (1964), the Captains Flat Formation extends for some 41 km. The southernmost outcrop is near Mount Baldwin at GR 208527, but the bulk of the formation crops out between Captains Flat and Bungendore (Canberra 1:100,000 sheet) • Synonymy and P1'evious Work Kenny and Mulholland (1940, 1941) and the staff of Lake George Mines Pty Ltd (1953) described the formation in some detail, noting the presence of two basalt flows and several suitable marker -horizons. 65 Glasson (1957 unpubl.) introduced the name "Captains Flat Beds" with continued usage by Gibbons (1962), Glasson and Paine (1965) , and others. Glasson (1957 unpubl.) also named the "Newtown Beds", a well-developed lithic tuff horizon, containing a large number of 66 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET shale inclusions and partings, and forming prominent outcrops and ridges. Oldershaw (1965) included this horizon with overlying conglomeratic beds in his Sinclair Conglomerate Member. Best et al. (1964) modified the name to the Captains Flat Formation. This usage was continued by Oldershaw (1965), who also designated the two member units -- the Yandyguinula Member and the Sinclair Conglomerate Member. Type Section within the township of Captains Flat the formation is well exposed on Town Hill (GR 216593), revealing a sequence of well-cleaved dark-grey shale, reworked lithic tuff, acid crystal tuff, dacite flows, and basalt flows. This is the type section for the formation. Description The formation as outlined by Oldershaw (1965) grades from the flows and tuffs of the Kohinoor Volcanics into a tuffaceous shale, becoming increasingly less tuffaceous as it grades upwards. Some 60 m of this 90 m section of shales is called the Yandyguinula Member (Sfy). Beds of tuff overlie the shales. These beds of reworked lithic tuff are dark-grey coarse-grained rocks consisting of fragments of shale, siltstone, sandstone, and fine-grained volcanics, together with rounded grains of quartz and feldspar, set in a fine-grained matrix of shale, quartz, and sericite. Graded bedding is evident in some of the thinner and finer grained beds, while crinoid ossicles and brachiopods have been found in the fragments of shale and in the matrix (appendix 1). Towards the middle of the formation, beds of light-grey crystal tuff are developed and are composed of fragments of quartz and plagioclase set in a matrix of minute grains of quartz, plagioclase, sericite, epidote, and calcite. Oldershaw (1965) considered that those tuffs which consist largely of broken and angular crystals with a subordinate matrix probably represent airfall tuffs, but others, which are composed of rounded crystals set in an abundant matrix containing crinoid ossicles, are probably reworked crystal tuffs. Dacite flows and tuffs are present in the middle of the formation and crop out towards its northern boundary (and the northern keel of the synclinorium). Glasson (1957) noted the development of very thin shales prior to the advent of the first basalt flow. These basalt flows crop out in both the northern and southern parts of the synclinorium, although no basalt has been found south of the Molonglo Fault. A few of the basalts have vesicular tops but none are spilitic or show pillow structure. Flow lines are not prominent and the grainsize is much finer than MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY that of the doleritic dykes. The basalt consists of small euhedral crystals of poorly twinned plagioclase, actinolite, biotite, minute flakes of sericite and biotite, needles of actinolite, and grains of epidote. The small aggregates of calcite are probably vesicular infillings. The basalts are separated by shales, tuffaceous shales and sandy shales. Glasson (1957) recognized only two separate basalt flows; they show excellent outcrops in certain places but appear to have a sporadic distribution along their strike. These flows crop out along the axis of the synclinorium between the Molonglo and Kanga Faults in the Michelago 1:100,000 sheet area. More recent work by L.W. Davis (pers. comm.) has indicated the presence of rocks of dioritic composition, particularly on the eastern side around Ballallaba Creek and to the south of Captains Flat close to the contact with the underlying Kohinoor Volcanics. Davis related these diorites and microdiorites to the basalts. Near the top of the formation, the Sinclair Conglomerate Member (Sfs) is developed. Yandyguinula Member (Sfy) 01dershaw 1965 Derivation This member is named after Yandyguinula Creek which flows near an outcrop of the member at GR 244735 on the Canberra 1:100,000 sheet. Distribution The Yandyguinula Member is best exposed along the eastern limb and around the sout!lern nose of the Captains Flat Synclinorium. Type area Oldershaw (1965) did not nominate a type area for the unit. Description It is a sequence of alternating thin beds of grey siltstone and shale, with beds ranging from 3 to 100 mm in thickness. Worm tubes have been found in the thicker beds of siltstone. Thickness The member has a thickness of between 45 and 60 m. 67 68 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET SincZair CongZomerate Member (Sfs) Stauffer et al. 1964 after W. 01dershaw Derivation The Sinclair Conglomerate Member is named after Sinclair Trig. Station (859 m) at GR 225664. Distribution This distinctive unit has been traced for 13 km along the western limb of the synclinorium and around the northern nose to the eastern limb (Canberra 1:100,000 sheet), but it has not been found in the southern nose. Type area Oldershaw (1965) did not nominate a type area for the unit, but it is probably best developed on the Canberra 1:100,000 sheet. Description The member comprises a sequence of interbedded shale and reworked lithic tuff. Some of the beds of reworked lithic tuff contain rounded boulders, up to 0.5 m across, of white quartzite, dark-grey slate, black slate, white dacite, and granite. Stauffer et al. (1964) described rounded quartzite pebbles with a matrix of crystal tuff in an outcrop at GR 225686. No current bedding or flute casts have been noticed. Thickness The member ranges up to 130 m in thickness. Thickness Oldershaw (1965) recorded a thickness variation of between 760 and 1220 m for the Captains Flat Formation at Town Hill (GR 216593). Boundary ReZationships The Captains Flat Formation rests conformably on the Carwoola Formation north of Hoskinstown (Canberra 1:100,000 sheet), but south of that point overlaps it and rests directly on the Kohinoor Volcanics. In the latter situation there is no evidence for an angular unconformity so the relationship is probably a conformable one. The boundary between the Kohinoor Volcanics and the Captains Flat Formation is a coarse crystal tuff/tuffaceous shale contact, emphasized by the presence of red jasper lenses at various points. Stauffer and Rickard (1966) misinterpreted the sequence around Hoskinstown, incorrectly showing the Captains Flat Formation overlain by the Carwoola Formation, but at the same time making correct modifications to the boundary between the two units. MIDDLE SILURIAN TO EARLY DEVONIAN STRATIGRAPHY Fauna and Age Fossil evidence is poor within the formation, but Glasson (1957) described a fine, green, fossiliferous tuffaceous shale band outcropping east of Vanderbilt Hill (GR 216582). This band contains fossils of Silurian age which were identified by A.A. Opik (appendix 1). On Newtown Hill there is a lithologically similar band containing a large number of crinoid stems. Oldershaw (1965) noted that the fossils are both indigenous and derived. Best et al. (1964) and Brunker et al. (1971) both indicated a Late Silurian age for the formation. 69 INTRUSIONS Numerous granite masses are present within the area of the Michelago 1:100,000 sheet. Both small plutons, such as the Urialla and Harrisons Peak Granites, as well as portions of two major batholiths -- the Murrumbidgee and Bega Batholiths -- are represented. These intrusions are of Late Silurian or Early Devonian age, the older bodies being emplaced along the western side of the area and younger bodies occupying the central and eastern zones. During the present study the genesis of the granites has only been superficially investigated, with major conclusions being based on the work of Chappell and White (1974) and White et al. (1974) . Studies of igneous masses within the Tasman Mobile Zone of eastern Australia have resulted in the recognition of two contrasting granite types by Chappell and White (1974) -- I-type and S-type. These two types may be distinguished by chemical, mineralogical, field relationship, and other criteria. Table 5 summarizes some of the distinctive chemical properties of the two types, while table 6 summarizes their petrological, field relationship, and economic characteristics. TABLE 5 SOME CHEMICAL PROPERTIES OF I-TYPE AND S-TYPE GRANITES (Modified after Chappell and White 1974, p. 173) I-types S-types Relatively high sodium, Na20 normally >3.2\ in felsic varieties, decreasing to >2.2\ in more mafic types Al <1.1 Na + K +Ca T C.I.P.W. normative diopside or <1\ normative corundum Broad spectrum of compositions from felsic to msfic Regular inter-element variations within plutons; linear or near-linear variation diagrams Relatively low sodium, Na20 normally <3.2\ in rocks with approx. 5\ K20, decreasing to <2.2\ in rocks with approx. 2\ K20 Al >1.1 Ns +K +Ca < > 1\ C.I.P.W. normative corundum Relstively restricted in composition to high Si02 types Variation diagrams more irregular 111111111111111111111111111111111111111111111111111111111111 0004941900 72 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET TABLE 6 SOME PETROLOGICAL,FIELD RELATIONSHIP, AND ECONOMIC CHARACTERISTICS OF I-TYPE AND S-TYPE GRANITES (Adapted from Chappell and White 1974) I-types Hornblende cammon in more mafic varieties and generally present in felsic varieties Sphene is a cammon accessory Apatite inclusions common in biotite and hornblende Mafic hornblende-bearing xenoliths of igneous appearance are typical Association with tungsten and porphyry- type copper and molybdenum deposits S-types Hornblende is absent Muscovite is common Biotite very abundant (~35') in more mafic varieties Monazite is an accessory Alumino-silicates, garnet, and cordierite may occur in xenoliths or in granites themselves Apatite occurs as discrete crystals Metasedimentary xenoliths common Hornblende-bearing xenoliths rare Tin mineralization found in highly silicic S-types The granites are interpreted as originating from partial melting of two different types of source material, i.e., igneous and sedimentary, and differences in the derived granites are inherited from the source rocks. According to Chappell and White (1974), metasedimentary xenoliths present in the S-type granites are not accidental types torn from the margins during emplacement but residual fragments from partial melting which have been carried from the source area. Mafic, hornblende-bearing xenoliths of the I-type granites are interpreted as being transported residual material, derived from an original igneous source. It is considered that I-type granites increase in abundance relative to the S-type granites eastwards across the Lachlan Fold Belt (White et al. 1974). Thus, for example, the Kosciusko and Maragle Batholiths are mainly composed of granites with metasedimentary xenoliths, the Berridale Batholith is composite in character, and the Moruya and Bega Batholiths contain granites with mafic xenoliths. INTRUSIONS Within the area of the Michelago 1:100,000 sheet, an attempt has been made to subdivide the granites into S-type and I-type granites on the basis of several chemical and petrological criteria (table 7). As a result of this study, all of the Murrumbidgee Batholith except one phase can be classified as S-type. The exception is the Murrumbucka Tonalite which is characterized by abundant hornblende-rich xenoliths. Both I and S-type characteristics are present in the Murrumbucka Tonalite and could be the result of contamination by basic or ultrabasic intrusions (Snelling 1960a). The other batholith present on the Michelago 1:100,000 sheet is the Bega Batholith. It is represented by the Boro Granite and the Jerangle Igneous Complex (Anembo Granodiorite and Towneys Creek Adamellite). The nature of these bodies is not so obvious, although the Anembo and Boro intrusions could be considered to be dominantly I-type and the Towneys Creek Adamellite dominantly an S-type granite. 73 Phases of the Michelago Igneous Complex are all grouped as I-type granites, although there is conflicting evidence in all cases. The Micaligo Adamellite is the most doubtful member of this suite of intrusions and it, like the Murrumbucka Tonalite, may have suffered some contamination of the melt by small basic bodies. In the Sapling Flat Igneous Complex the Wangrah Adamellite is tentatively classified as an S-type granite and the Danswell Creek Granodiorite as an I-type intrusion. Of the remainder of the minor intrusions, geochemical and petrological evidence suggests that most may be regarded as S-type granites, although conflicting evidence exists, particularly in the case of the Watch Box Granite. Minor flakes of molybdenum are more indicative of an I-type body. In general it must be emphasized that very little geochemical data is available for most of the intrusions on the Michelago 1: 100,000 sheet. Such information as is provided has come from a variety of sources over a considerable period of time and subsequently there is no standardization of results. The overall conclusion is that the Murrumbidgee Batholith is an S-type and the Bega Batholith a composite batholith. All intrusions but the Michelago Igneous Complex dominantly possess S-type characteristics. TABLE 7 -..J01>- CLASSIFICATION OF GRANITES INTO I-TYPE OR S-TYPE ON THE BASIS OF CHEMICAL AND PETROLOGICAL CHARACTERISTICS Intrusion \ Na20 Al ~l\ \ Si02 Hornblende Xenoliths Mineral- \ K20 Na +K+Ca norm. corundum ization T Murrumbidgee Batholith Clear Range Granodiorite 5 S 5 - S S Murrumbucka Tonalite ?I S I I I I Callemondah Granodior i te S S S - S S - ~Shannons Flat Adamellite S S S - S ?S - 0 Tharwa Adamellite S S I - S ?S - t-t0 Leucogranites S ?S ?S - S - - Gl Booroomba Leucogranite· - - - - S - 0< 0 Bega Batholith '"':l 0-,3Anembo Granodiorite I S I - I ?1 or S - ::I: Towneys Creek Adamellite S S I - S - - t'l Bora Granite 5 S I - I ?I or S - 3: H () MicheZago Igneous Comp~ex ::I: t'lMonkellan Granodiorite I S I ?I I - - t-t Onslow Granodiorite I S I ?I I I - :x>Gl Micaligo Adamellite ?S 5 I - I - - 0 Koolambah Adamellite I S I - I I - f-' .. Sapling nat Igneous Comp~ex f-'0 Danswell Creek Granodiorite ?S S I - I ?S - !? Wangrah Adamellite S ?S I - 5 - - 00 0 Other bodies Ul Bredbo River Adamellite* - - - - S - - ::I:t'l Tinderry Granite ? ?S I - S - - t'l Harrisons Peak Granite· - - - - S 0-,3 Urialla Granite I S S - S Watch Box Granite* - - - - S - I Good Good Adamellite· - - - - ?S These granites have not been chemically analysed. SILURIAN INTRUSIONS SILURIAN Cotter Anticlinorium MURRUMBIDGEE BATHOLITH (gmh, gma, gmt, gmn, gmr, gml, gmb) modified from Browne 1929 Derivation The name of the batholith is derived from the Murrumbidgee River which flows close to its eastern boundary. Distribution The batholith crops out over some 1400 km 2 , stretching for 95 km from north of Cooma almost to the Cotter Dam (Brindabella 1:100,000 sheet), southwest of Canberra. The batholith intrudes low-grade regionally metamorphosed Late Ordovician sediments. Synonymy and Previous Work Browne (1929) used the term "Murrumbidgee Bathylith". The batholith has been studied and well documented since the early 1900's, with significant contributions by Browne (1914, 1944), Joplin (1943), Legge (1937), Sharp (1949 unpubl.), Joplin et al. (1953), Snelling (1957 unpubl., 1960), Best et al. (1964), Brunker et al. (1971), and particularly Joyce (1970a unpubl., 1973a, b). One of the leucogranites is included in a geochemical study by Kolbe and Taylor (1966), followed by a more detailed geochemical investigation of the batholith by Joyce (1973b). Isotopic age dating has been undertaken by Evernden and Richards (1962), Joplin (1962), Pidgeon and Compston (1965) and J. Roddick (pers. comm.). The following notes are mainly a resume of Joyce's and Snelling's work. Description The batholith consists of eleven named intrusions, ranging in outcrop area from 5 km 2 to 655 km 2 , together with many stocks, bosses~ and dykes of unnamed microgranites, totalling an additional 205 km Six named intrusions are represented wholly or partially on the Michelago 1:100,000 sheet. On the basis of field characteristics and inferred genetic relationships, Snelling (1957) divided the rocks into three groups uncontaminated granites, contaminated granites, and potassic leucogranites. Joyce (1970) retained Snelling's groupings and terminology but added the proviso that the terms "uncontaminated" and "contaminated" meant poor and rich in sedimentary xenoliths respectively, regardless of whether significant reaction had occurred between xenoliths and magma. 75 76 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Textural differences between the three groups of granitic rocks imply different styles of emplacement and rates of crystallization. Thus, the coarse, fairly massive texture of much of the uncontaminated granite indicates a rather passive emplacement and slower crystallization, while the finer grained, conspicuously foliated texture of the contaminated phases suggests final emplacement in a largely solid state. Textures of the leucogranites vary from medium-grained porphyritic to aplitic, indicating that they crystallized fairly rapidly owing either to cooling or loss of water pressure. In outcrop on the Michelago sheet, the rocks of the batholith form typically large rounded to elongated tors, the amount of elongation increasing with proximity to the major shear zones. Thus, near the Murrumbidgee Fault, the Clear Range Granodiorite is characterized by very elongated biotite flakes and a coarse mylonitic texture. Weathering takes place more rapidly under these conditions, whereas exfoliation is typical with the rounded boulders. Although contacts between intrusions can usually be located to within a few metres, actual intrusive relationships between the medium or coarse-grained bodies are often obscured by weathering. Topographically the area of outcrop of the batholith on the Michelago sheet is rugged, especially along the eastern side where the Clear Range is dominated by Mount Clear (1603 m). In addition to the meridionally trending Naas and Gudgenby Rivers, the range is dissected by numerous northeast-trending streams, while on the western side of the batholith (on the Tantangara 1:100,000 sheet), the main streams trend northwest. Stream pattern control will be discussed further in the section on structures. Boundary Relationships The batholith lies between two major fault zones, the Murrumbidgee Fault to the east and the Cotter Fault to the west. Consequently, the eastern margin is in faulted contact with Silurian acid volcanics and sediments. Pleistocene lake deposits and alluvium and several small outcrops of Tertiary basalt overlie it, particularly in the southern part. Along its western margin in the Michelago area, the batholith has a well-developed contact metamorphic aureole which reaches biotite grade and varies in width from 100 m to 1500 m; for instance, au Roberts Mountain (GR 826159) a thin section of a typical hornfels shows it to be a metasiltstone with biotite and muscovite flakes in the matrix (appendix 2-1). This recrystallized rock is fairly resistant to weathering. No contact metamorphism is developed along the faulted eastern margin of the batholith. SILURIAN INTRUSIONS There is no evidence of extensive incorporation of local country rock at the margins of any of the granitic phases. The few recognized xenoliths rafted from the enclosing hornfels contrast markedly with the typical xenoliths of the contaminated phases in possessing angular shapes and displaying little evidence of appreciable chemical exchange with the enclosing granitic rock. Age Age relationships must be inferred mainly from the general shapes of the intrusions and the curvature of their mutual boundaries. Joyce (1973b) believed that the Shannons Flat Adamellite had been emplaced first, followed by the Bolairo, Callemondah, and Clear Range Granodiorites and the Willoona Tonalite at an approximately similar time. However, work by Owen et al. (1974a) indicates that the Clear Range Granodiorite was emplaced before the Shannons Flat Adamellite. Examination of the boundaries between the two masses reveals small veins of the latter intruding the former. Thus the sequence of intrusion deduced for the phases of the Murrumbidgee Batholith as represented on the Michelago 1:100,000 sheet is: 1. The synchronous emplacement of the Clear Range Granodiorite, the Murrumbucka Tonalite, and the Callemondah Granodiorite. 2. The emplacement of the Shannons Flat Adamellite and the Tharwa Adamellite. Their relative sequence of intrusion is not obvious for two main reasons; (a) there is only a small area of contact between the two phases, and (b) the area of contact shows an interfingering of granitic types, with insufficient outcrop available to indicate which type has the dyke form. 3. The Booroomba Leucogranite and the other minor bodies of leucogranite in the form of stocks, bosses, and dykes clearly intrude all previously mentioned components of the batholith. Radiometric age dating has been carried out on various phases of the batholith (see appendix 4), giving variable results depending on the degree of recrystallization the rock has undergone (for example, the Tharwa Adamellite was sampled close to the Murrumbidgee Fault) and on the age-dating method used. The most recent age-dating results (J. Roddick pers. comm., Roddick and Compston 1976) using Rb-Sr data on biotite, plagioclase and K-feldspar, indicate an age of 423 ± 4 m.y. for most of the phases, and suggest relatively rapid cooling of the rocks after intrusion. 77 78 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Roddick and Compston (1976, p. 232) reached the conclusion that: "the emplacement of the whole batholith may have spanned an interval from 424 ± 2 m.y. to 414 ± 4 m.y. or alternatively could be viewed as essentially a single event at 424 ± 2 m.y. The radiometric ages are thus completely consistent with the conclusion of Joyce (1973b) that all the components of the Murrumbidgee Batholith were closely related to each other in time". CONTAMINATED PHASES The contaminated phases of the Murrumbidgee Batholith are the Willoona Tonalite, the Stewartsfield Granodiorite, the Bolairo Granodiorite, the Callemondah Granodiorite, the Clear Range Granodiorite, and the Murrumbucka Tonalite (Joyce 1973b), of which only the last three appear within the Michelago sheet area. Although they range from granodiorite to tonalite, individual intrusions have fairly restricted compositions. The features common to the group are the fine to medium-grained texture, the predominant mineralogy of quartz, feldspar, and brown biotite, minor muscovite, a conspicuous mica foliation, blue quartz, and abundant finer grained biotite-rich xenoliths. The last are invariably rounded, usually discoid, with a size range from single xenocrysts up to large xenoliths about 400 mm in diameter, and tend to be aligned with the strong mica foliation of the contaminated granites. Some contrast sharply in grainsize with their host, and have sharp boundaries, but many are veined and corroded by the enclosing rock so that their boundaries become diffuse and they appear as finer grained dark streaks and patches in the granodiorites and tonalites. Most of the xenoliths consist of foliated or schistose- aggregates of plagioclase, biotite, and quartz, many with streaky finer grained areas of muscovite and biotite; but some consist of fine muscovite and biotite; others contain actinolite, biotite, plagioclase, and quartz; and a few consist principally of quartz with lesser amounts of biotite or plagioclase. All minerals in the xenoliths are strained, grain boundaries are ragged, and most grains exhibit bending, fracturing, and undulose extinction. The mineralogy, texture, and mode of many xenoliths indicate a metasedimentary origin. CLEAR RANGE GRANODIORITE (gma) Snelling 1960 Derivation The Clear Range, which lends its name to this intrusion, forms the main topographic feature of the area of outcrop and the boundary of the Australian Capital Territory. SILURIAN INTRUSIONS Distribution The Clear Range Granodiorite dominates the eastern side of the Murrumbidgee Batholith and lies largely on the Michelago 1:100,000 sheet. It covers a total area of some 440 km 2 • Type Area Previous workers have failed to define a type area for the granodiorite. However, Joyce (1973a) did carry out several chemical analyses on specimens of the Clear Range Granodiorite. One of these specimens (Australian National University catalogue number 20535) is considered to be fairly representative of the granodiorite and therefore, the location where this specimen was collected (i.e., GR 814533) is thought to be a suitable type area for the granodiorite (appendix 4). Desoription The Clear Range Granodiorite is the largest body of contaminated granite and is more variable than, though similar to, the other contaminated granites in average composition. Basic phases are best developed in its southern extremity and it is here that the Murrumbucka Tonalite becomes prominent. Northwards the Clear Range Granodiorite is replaced by the Shannons Flat Adamellite in the northwest, by leucogranites to the north, and by the Tharwa Adamellite to the northeast. As in the other contaminated phases, muscovite is a notable constituent, occurring as an apparently primary mineral as well as an alteration product of both biotite and plagioclase in the same manner as in the uncontaminated phases. Its presence is a reflection of the rather high aluminium content (relative to alkalis and calcium) of all the components of the batholith. Appendix 3 gives chemical analyses of the granodiorite. Boundary ReZationships The Clear Range Granodiorite intrudes the Adaminaby Beds, and a thermal metamorphic aureole from 100 m to l~ km wide has developed (see section on the Adaminaby Beds). MURRUMBUCKA TONALITE (gmt) Snelling 1960 Derivation The name Murrumbucka Tonalite is derived from Murrumbucka Creek, Murrumbucka Trig. Station, or Murrumbucka Gap, all to the southeast of Bredbo, on the Cooma 1:100,000 sheet. 79 80 Distribution GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The tonalite occurs at the southeastern extremity of the Murrumbidgee Batholith, extending from Bredbo in the north towards Cooma (refer to Canberra and Bega 1:250,000 Geological sheets). Although the tonalite has an outcrop area of about 51 km 2 , only a small portion actually lies on the Michelago 1:100,000 sheet. Spring Vale CreekatGR 870173 would form its northern limit. Synonymy and Previous Work Browne (1944) and Joplin (1943) were early workers in the area, the former providing maps and descriptions, and the latter rock analyses. Joyce (1973b), in more recent work, recommended that the term Murrumbucka Tonalite be discontinued and the mass be included with the Clear Range Granodiorite. Type Area NO type area has been defined. However, the tonalite is well represented at MurrumbuckaGap (GR 895106 on the Cooma 1:100,000 sheet). Desaription Snelling (1960) designated the southeastern part of the batholith the Murrumbucka Tonalite because of its unique possession of hornblende-rich xenoliths and accessory hornblende in addition to the biotite-rich xenoliths typical of the other contaminated intrusions. In thin section the tonalite is composed of quartz, plagioclase (andesine), and biotite, with accessory microcline hornblende, apatite, epidote, and tourmaline. The plagioclase is poorly zoned but basic cores are common. The texture is the same as that of the contaminated granodiorites, but in many cases the rock has suffered considerable deformation followed by recrystallization. The result is strain- free quartz and biotite with a granulitic texture and euhedral epidote crystals; the last were once thought (Joplin 1943) to be primary in origin. Chemical analyses of the tonalite are given in appendix 3. Boundary ReZationships The boundary between the Clear Range Granodiorite and the Murrumbucka Tonalite is gradational, as there is a gradual decrease in the content of K-feldspar to the south of Mount Clear (GR 862276). SILURIAN INTRUSIONS CALLEMONDAH GRANODIORITE (gmh) Snelling 1960 Derivation The granodiorite is named after "Callemondah" homestead (GR 805223). Distribution On the Michelago 1:100,000 sheet the granodiorite is represented only by its eastern extremity, cropping out between GR 805247 and GR 805225 near "Callemondah" homes'!:ead. The Callemondah Granodiorite lies towards the central southern part of the Murrunbidgee Batholith. This particular phase is one of the smaller units of the batholith, having a total area of only 22 km 2 • Type Area As the. main area of outcrop falls within the boundaries of the Tantangara 1:100,000 sheet, the reader is referred to Owen et al. (1974b, in press). Desoription In composition the granodiorite would appear to conform to the typical granodiorite composition within the batholith. Chemical analyses are given in appendix 3. Boundary ReLationships The granodiorite lies on the western side of the batholith, with Late Ordovician metasediments surrounding the greater portion of it including that part on the Michelago 1:100,000 sheet. The remaining boundary is formed with the Shannons Flat Adamellite. UNCONTAMINATED PHASES This group consists of the Shannons Flat Adamellite and the Tharwa Adamellite, both of which are coarse grained and poor in xenoliths. SHANNONS FLAT ADAMELLITE (gmn) Joyce 1973b modified from Snelling 1960 Derivation The name of the adamellite is derived from the village of Shannons Flat at GR 761217 on the Tantangara 1:100,000 sheet. Distribution The Shannons Flat Adamellite is the largest component of the Murrumbidgee Batholith being some 665 km 2 in area, but only a few square kilometres crop out within the boundaries of the Michelago 1:100,000 sheet, in the vicinity of Honeysuckle Creek (GR 820612). 81 82 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Synonymy and Previous Work The original name, first introduced by Snelling (1957 unpubl., 1960), was "Shannons Flat Granodiorite". Type Area No type area was defined by Snelling (1960), but typical outcrop is found along the Apollo Road between GR 827610 and GR 815608. Desoription Snelling (1957 unpubl., 1960) originally defined and named this body the Shannons Flat Granodiorite, with continued usage of the name by Best et al. (1964), and Vallance (1969). Joyce (1970a, 1973a, 1973b) subsequently re-analysed the rock and redefined it asa coarse-grained adamellite conspicuously porphyritic in microcline crystals up to 40 mm in length. Snelling regarded the rock as typically massive, but Joyce considered most areas to have a recognizable mica foliation. primary minerals are quartz, microcline, plagioclase, and brown biotite, all showing varying degrees of strain. Minor accessory minerals are apatite, pyrite, and zircon. Secondary minerals formed by breakdown of plagioclase and biotite are common, with the cores of many plagioclase grains altered to sericite and epidote and some biotite altered to chlorite and epidote. A common type of biotite alteration, especially in the most sheared specimens, consists of marginal alteration to fine-grained muscovite, magnetite, ilmenite, and quartz. Such formation of muscovite may be related to the high aluminium content of biotites of the adamellite. A few samples contain rare large flakes of apparently primary muscovite. Xenoliths are virtually absent in the Shannons Flat Adamellite. The one or two that have been found resemble those in the Tharwa Adamellite. Chemical analyses of the adamellite are given in appendix 3. THARWA ADAMELLITE (gmr) Snelling 1960 Derivation The Tharwa Adamellite is named after, and crops out in the vicinity of, Tharwa, at GR 874684. Distribution In the Michelago sheet area the adamellite lies between Mount Tennent (GR 352638) and the Murrumbidgee River, with the Tharwa SILURIAN INTRUSIONS Adamellite extending from north of Tharwa to GR 893598, west of Angle Crossing. The adamellite covers a total area of some 45 km 2 • Synonymy and Previous Work Apart from Clarke (1860) who recorded the presence of granites along the west bank of the upper Murrumbidgee, and Mahony and Taylor (1913) who briefly described the granite from Tharwa, Snelling (1960) was the first to attempt any description of the Tharwa Adamellite. ~peA~a No type area has been designated by previous workers. It is considered that the adamellite is best represented at Tharwa itself. Desoription The Tharwa Adamellite differs from the Shannons Flat Adamellite primarily in having a greater abundance of microcline, more strongly zoned plagioclase, and a conspicuously sheared texture. Xenoliths are small and sparsely distributed in the adamellite. They have a grainsize of less than 0.5 rom and consist of quartz, plagioclase, brown biotite, and microcline, all of which are strained and have ragged grain boundaries. The plagioclase is abundantly twinned and conspicuously zoned. Modally the xenoliths are granites and adamellites, but the abundance of feldspar and quartz porphyroblasts testifie3 to extensive modification and the original nnture of the xenoliths is uncertain. The adamellite has two directions of foliation, which are particularly well represented in the vicinity of Tharwa itself. Both primary and superimposed secondary foliations are present, the primary emphasized by the alignment of the sparse xenoliths and the secondary promoted by the intensity of and proximity to the Murrumbidgee Fault. Chemical analyse of the Tharwa Adamellite are given in appendix 3. LEUCOGRANITES Rocks of this general grouping differ widely in texture but petrologically are granite sensu stricto and are poor in ferromagnesian minerals. The group includes the Yaouk and Booroomba Leucogranites, the Westerly Muscovite Granite, and numerous smaller unnamed bodies of leucogranite (Joyce 1973b). Of these bodies, only the Booroomba Leucogranite and the small bodies (gml) are found in the Michelago area, and they are particularly concentrated around the northern limit of the batholith near Mount Tennent at GR 852638. 83 84 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Small dykes of granite porphyry, microgranite, and aplite are common as minor intrusions in the coarse-grained leucogranites and the uncontaminated phases. The microgranites include porphyritic and equigranular varieties, the latter grading into aplites witQ increase in grainsize. The porphyritic varieties carry euhedral crystals of quartz, microcline, sodic oligoclase, and biotite in a fine-grained groundmass of the same minerals and muscovite. Quartz and microcline crystals may be up to 5 mm in length, with plagioclase and biotite up to 1 mm. The equigranular varieties have an average grainsize of 2 mm. Chemical analyses of the leucogranites are given in appendix 3. BOOROOMBA LEUCOGRANITE (gmb) Richardson 1975 Derivation The Booroomba Leucogranite is named after "Booroomba" homestead at GR 793710 on the Brindabella 1:100,000 sheet. Distribution Outcrop of the leucogranite is concentrated at the northern end of the Murrumbidgee Batholith around Mount Tennent (GR 852638) and to the northwest of the trig. station, with further outcrop on the neighbouring Tantangara 1:100,000 sheet. A minimum area of some 52 km 2 is covered by the leucogranite, with 22 km 2 occurring on the Michelago 1:100,000 sheet. Type Area Best representation of the Booroomba mass is found on the summit of the Mount Tennent, where large exposures of the rock may be easily examined. Desoription As mentioned above, the leucogranites possess a varied texture and this also applies to the Booroomba Leucogranite, although in the type area it appears to have a mainly coarse texture. Muscovite is well displayed on the fresher rock surfaces. At some localities the leucogranite is found to have a higher mafic content. Boundary ReZationships In shape the western part of the Booroomba Leucogranite is a fairly compact body, almost rounded in form, but the eastern portion extends into an elongate body trending roughly southward. The Tharwa and Shannons Flat Adamellites and the Clear Range SILURO - DEVONIAN INTRUSIONS Granodiorite are intruded by the mass, and the leucogranite boundary is most obvious against the mafic-rich granodiorite (for example around GR 830682). SILURO - DEVONIAN Canberra Synclinorium LIVINGSTONE PORPHYRY (5-01) Richardson 1975 Derivation Livingstone Trig. Station (932 m) at GR 943424 is the source of the name. Distribution Extending in a narrow belt from north of Miche1ago at GR 935549 to Co1inton at GR 942357, the porphyry is some 19 km in length. The main area of outcrop lies between the Murrumbidgee River and the Monaro Highway, although minor separated masses are found west of the river, for example at GR 927510. The porphyry covers an area of approximately 19.5 km 2 • Synonymy and Previous Work 85 Brown (1928 unpub1.) mentioned quartz porphyries around Co1inton and Miche1ago. Sharp (1949 unpub1.) further described the porphyry, terming it a quartz diorite porphyry or blue gneiss quartz porphyry, with associated alaskites and ap1ites. Joplin et a1. (1953) termed the porphyry a granite porphyry and granodiorite porphyrite. Type Area The porphyry is typified by outcrop at GR 945423. Desoription Of dacitic composition, the porphyry consists of crystals of quartz, plagioclase (oligoclase/andesine), biotite, apatite, sphene, and alkali feldspar, set in a matrix of plagioclase, quartz, alkali feldspar, chlorite, and sericite plus granular epidote. Grainsize may be as coarse as 6 rom (quartz) but generally ranges between 0.5 and 2 rom with a 0.04 rom matrix. Xenoliths are infrequent but are present. They are generally fine-grained rocks of rhyodacitic{?) composition (appendix 2-22) with sharp boundaries and showing little contact metamorphism. Characteristically the porphyry contains large xenocrysts{?) of pink orthoclase feldspar up to 30 rom in length and present in a frequency of roughly 1 per 230 cm 2 • 86 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The porphyry, which is typically a greenish grey in colour, crops out as highly weathered, rounded boulders, particularly on the ridges. Jointing is common in the massive porphyry. Associated with the porphyry (and included on the map with it) are small outcrops of fine to very coarse-grained alkali feldspar and quartz-rich rocks. They are particularly common between Livingstone Trig. Station and Michaligo Creek. Sharp (1949) described the fine to medium-grained rocks with saccharoidal textures as aplites containing reddish-pink feldspar, quartz, and chloritized ferromagnesian minerals. Alaskites, with similar mineralogy but much coarser grained (7 to 10 mm), are sometimes porphyritic in feldspar with phenocrysts up to 20 mm in length. The alaskites are well represented at GR 938461, south of the Micaligo Creek. Boundary Relationships The Livingstone Porphyry is a sill-like intrusive mass with its boundaries showing a crude parallelism to the eastern boudary of the Murrumbidgee Batholith. The porphyry's meridional trend results in its boundary being rougly aligned with the strike of the Colinton Volcanics and the Bransby Beds. This creates difficulty in locating an intrusive contact. One such contact is found at GR 936528 near the northern end of the porphyry where it intrudes fine-grained southward-dipping tuffs of the Bransby Beds (photo 6). More commonly, however, the boundary between the tuffs and sediments and the porphyry is in an area of no outcrop. Displacement of the Livingstone Porphyry has possibly occurred along the line of the Collingwood Fault. Though the fault is clearly discernible to the south near "Collingwood" homestead, there is relatively little evidence for its presence between the Monaro Highway and the Murrumbidgee River, apart from minor amounts of quartz float and the alignment of the boundary of the porphyry. Age An Early Devonian age is postulated for the Livingstone Porphyry as it intrudes the Bransby Beds of Late Silurian to earliest Devonian age. BULLANAMANG PORPHYRY (S-Du) Richardson 1975 Derivation The porphyry acquires its name from the Parish of Bullanamang in the County of Beresford. Distribution SILURO - DEVONIAN INTRUSIONS 87 Located to the northwest of Bredbo, the porphyry lies largely to the north of the Murrumbidgee River with possible minor extensions to the south. It covers an area of approximately 0.4 km 2 • Synonymy and Previous Work First described by Browne (1944) as "granite - porphyries" and Joplin (1943) as "quartz-diorite-porphyrite", the description of the unit varied in following years between "granite porphyries and granodiorite porphyrites" of Joplin et al. (1953) and "undifferentiated granitic rocks" of Best et al. (1964). Type Area Fairly weathered but representative outcrop of the porphyry is present in the creek bed at GR 916212. Desoription The Bullanamang Porphyry is similar in composition to the Livingstone Porphyry, but, unlike it, is less readily mappable in the field. As described by Browne (1944, p. 168) the outcrop "really appears to be to some extent a congeries of thin lenses or sills" rather than a solid mass. Abundant large bipyramidal phenocrysts of quartz up to 9 rom in length with plagioclase, biotite, and minor hornblende (the latter usually altered to chlorite and epidote) appear in a finely altered granular groundmass. Browne (1944) also noted small intrusions of aplite and of coarse pink acid granite or alaskite closely associated and evidently comagmatic with the porphyry. Along the eastern boundary of the porphyry one such "granite" was found at GR 923239. The rock is a mildly altered subporphyritic granite containing perthitic alkali feldspar, quartz, and plagioclase (andesine) packed together and cut by thin veins of quartz. Grainsize varies between 1 and 10 rom (appendix 2-23). Joplin (1943) gave a detailed petrographic description of the porphyry. Boundary Relationships As noted above, the porphyry is intrusive in nature but with very little direct contact in outcrop between the porphyry and the 88 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET intruded Bransby Beds. Shearing related to the Murrumbidgee Fault is strongly developed along the eastern margin as well as parts of the western margin. Age As the porphyry intrudes the Late Silurian-Early Devonian Bransby Beds, an Early Devonian age is postulated. COSGROVE PORPHYRY (S-Do) Richardson 1975 Derivation The Cosgrove Porphyry is named after the Cosgrove Trig. Station (~9l m) at GR 938151. Distribution Located south of Bredbo, the porphyry lies between the Monaro Highway and the Bredbo River. It covers only 1 km 2 • Synonymy and Previous Work This porphyry was described by Pillans (1974 unpubl.). Type Area Typical specimens are found at GR 935165. As it crops out as a large, prominent hill north of Cosgrove Trig. Station, the porphyry would appear to be fairly resistant to weathering. Prominent quartz and feldspar phenocrysts are set in a dark, fine-grained groundmass. Pillans (1974) ~oted that quartz overgrowths (developed in situ) and myremekitic quartz - feldspar intergrowths suggest an intrusive origin. Boundary ReZationships From field evidence, Pillans (1974) concluded that the porphyry had an intrusive origin. Along the margin of the porphyry, at GR 941163 and GR 935159, hydrothermally altered rocks are present, while in a creek at GR 942162 the intrusive contact is clearly visible. Age An age of Late Silurian-Early Devonian is postulated. DEVONIAN INTRUSIONS DEVONIAN Cullarin Anticlinorium MICHELAGO IGNEOUS COMPLEX (gc, gco, gcm, gcc, gck, gcp) Richardson 1975 modified from Joplin et a1. 1953 Derivation The village of Michelago at GR 960460 on the Monaro Highway is the source of the name of the Michelago Igneous Complex. Distribution Extending meridionally over some 32 km from just north of the Bredbo River to GR 006493, the mass attains an average width of 4 km. In form the Michelago Igneous Complex consists of two distinct masses which have been subdivided into several phases. The two masses are separated from one another as a result of considerable displacement along the Collingwood Fault. This fault forms the southwestern boundary of the northern body and the northeastern boundary of the southern Michelago mass. The southern mass, covering some 32 km 2 , is approximately half the size of the northern mass which has an area of outcrop of 60 km 2 • In shape they are both fairly elongate with several boundary offsets caused by northwest-trending faults. Synonymy and Previous Work . Brown (1928 unpubl.) was the first to describe and name the "Michelago Granite", but his remarks related only to the northern body. His granite boundary was fairly accurate and demonstrated his recognition of several faults, but he attempted no subdivisions within the mass. Joplin et al. (1953) first published the name "Michelago Granite", but again only applied the term Michelago to the northern body, choosing to leave the southern body unnamed. Best et al. (1964) published the name in reference to both northern and southern bodies, followed by Packham (1969), Brunker et al. (1971), and Strusz (1971). In a geochemical sampling exercise in the vicinity of Michelago, Ivanac and Marshall (1965) took several granitic rocks from within the northern body and indicated copper, lead, and zinc contents. Slepecki (1973) made reference to the "Michelago Batholith". II~mmlll~II~~ 0004941901 89 90 DeBcriptiOI1 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The ~lichela90 Igneous Complex has been subdivided by field mapping and petrological work into four named and several minor unnamed phases. The Micaligo and Koolambah Adamellites were possibly intruded first, followed by the Onslow and Monkellan Granodiorites and lastly by minor porphyritic and marginal leucogranitic phases. Typically the Michelago Igneous Complex is a highly weathered body (photo 10) with the major portion cropping out as rounded tors. The only rugged areas are between Strike-A.-Light Creek and eoliotan Hill, and along the southeastern s1de of the southern body. Contact metarnorptis~ is not pronounced, and there is very little indication of sediments being affected, apart from minor local silicification. Minor granite and porphyry stringers invade the country rock, particularly around the northern body. Along the eastern margin, which is well exposed in a road cutting on the Bredbo - Jcrangle road at GR 052227 (photo 7), numerous granite Photo 7. Intrusive contact between the ~ic~ela90 Igneous COMplex (lighter coloured, veinedl and the Ordovic1an ~oxlow Beds, present In a road cutting on the Bredbo - Jerangle road at GR 052221 DEVONIAN INTRUSIONS tongues intrude and envelop the sediments but have caused comparatively little alteration, indicating that the magma was fairly fluid and had a low to medium temperature at the time of intrusion. ----I 91 I However, Slepecki (1973) believed the northeast margin of the southern body along Ryans Creek to have a marked contact aureole defined by spotted schists with andalusite/cordierite retrogressed to sericite aggregates with a maximum size of 2 rom. Within the granite itself he described a foliation developed subparallel to the granite contact, mainly characterized by alignment and slight elongation of quartz grains and alignment of small elliptical xenoliths. However, this foliation could be partially related to the presence of the Collingwood Fault. The Michelago Igneous Complex intrudes Ordovician phyllite, slate, and greywacke (Foxlow Beds) and comes in contact with Silurian sediments on:y along the major faulted boundary, i.e., the Collingwood Fault. In the vicinity of "Collingwood" homestead and Colinton Trig. Station (GR 980283) the Early Silurian Ryrie Formation and the Late Silurian Cappanana Formation and Colinton Volcanics are faulted against the complex, the lithological change being dramatically portrayed by a massive ridge of vein quartz, originally called the 'toll bar' by Brown (1928) (photo 8). Internal boundary relationships are rarely observed, mainly a result of the style of outcrop and degree of weathering of the complex. One intrusive relationship has been observed around GR 015330, between porphyry and granodiorite. Age No age dating has been carried out successfully on the various phases of the Michelago Igneous Complex because of the degree of alteration present within the rocks (see appendix 4). Correlation with other granites within the area, e.g., the Tinderry Granite, suggest a time of formation at the close of the Silurian Period. NORTHERN MICHELAGO BODY This body has been subdivided into several phases, of which three have been named -- the Monkellan and Onslow Granodiorites and the Micaligo Adamellite. The Micaligo Adamellite is by far the largest in area, the granodiorites both being of limited extent. Minor porphyries and leucogranites constitute a small portion of the mass. 11111/11111/ 111/1111/111111111/111111 1/111111/1 1/11111111111 0004941920 92 GEOLOGY OF 'niE M,10IELAGO 1: 100,000 SHEET Photo 6. Extensive quartz reefs are formed along the line of the Collingwood Fault. This particular outcrop appears near "Collingwood" homestead at GR 974]36 MoNKELLAN GRANODIORITE (gem) nov. Derivation The Monkellan Granodiorite is named after the Parish of Monkellan, County of Murray, in which part of it occurs. Distribution This phase dominates the northern extremity of the northern Michelago body, croppin~ out in the vicinity of Micaligo Creek at GR 002465. Some 3.2 km are covered by this phase. 1[111[11111111 II II~IIIII [II] 0004941930 DEVONIAN INTRUSIONS Type Area A typical example occurs at GR 005464, just to the southeast of "Tea Tree Creek" homestead (appendix 2-24). Desoription Enriched in mafics, the granodiorite contains both biotite and hornblende which are generally associated in clots. The clots range between 5 and 10 mm in size, consist of biotite, hornblende, plagioclase, and quartz, and show mild alteration. The contact zone between the clot and the host rock is composed almost entirely of poikilitic quartz. The host rock consists of biotite, quartz, microcline, plagioclase and opaques but has no hornblende. Again mild alteration has taken place. The host rock is a biotite granodiorite while the clots approximate in composition to a hornblende biotite quartz diorite. The texture suggests that the rock is a hybrid biotite and hornblende granodiorite. A petrological description is given in appendix 2-24 and a chemical analysis in appendix 3. ONSLOW GRANODIORITE (gco) nov. Derivation The Parish of Onslow, County of Beresford, lies to the immediate east of the Onslow Granodiorite. D-i-stribution One of the smaller phases of the Michelago Igneous Complex, the Onslow Granodiorite crops out along the eastern margin of the northern Michelago body, to the south of the headwaters of Cockatoo Creek, between GR 032347 and GR 016311. The granodiorite covers only 2.2 km 2 • Type Area The granodiorite is well represented at GR 016322. Desoription In hand specimen the rock is a medium-grained mafic-rich (20 per cent) granodiorite with bluish-coloured quartz crystals, the latter a result of the mild granulation the rock appears to have undergone in its last phases of crystallization. 93 /111111111/1111/111/11111111111111111111111111/ 1111/ III/ I111 0004941940 94 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Thin section analysis (appendix 2-25) reveals a plagioclase (andesine), quartz, biotite, hornblende, and alkali feldspar, with minor magnetite and rare zircon and apatite. Xenoliths with a higher mafic content than the host granodiorite are present. A chemical analysis of the granodiorite is given in appendix 3. In outcrop, the Onslow Granodiorite forms rounded boulders. It is a marginal phase which probably developed at a later date than the other phases. The Onslow Granodiorite has an even distribution of hornblende and biotite, thus differing from the Monkellan Granodiorite which has its hornblende associated with the biotite crystals in clots. M!CALIGO ADAMELLITE (gee) nov. Derivation The Micaligo Adamellite, the largest phase of the northern Michelago body, is named after "Micaligo" homestead, at GR 000400. Distribution The adamellite occurs along most of the extent of the northern Michelago body, and covers an area of at least 35 km 2 • Type Area This biotite hornblende adamellite is well represented in the vicinity of "Micaligo" homestead. Specimens have been described from GR 993405 (appendix 2-26). Description Specimens from the type area contain plagioclase (oligoclase) mantled with albite, biotite, and perthitic alkali feldspar, set in a matrix of quartz, biotite, perthitic alkali feldspar, plagioclase, hornblende, and minor magnetite and muscovite. Mild alteration is evident. Variations in the composition and texture are common but at no stage does the hornblende appear to equal the biotite in abundance. No xenoliths are present within this phase. A chemical analysis of the adamellite is given in appendix 3. DEVONIAN INTRUSIONS Outcrop is poor within the central and northern part of the Micaligo Adamellite. Here alluvium tends to mask the body leaving only sporadic boulders. MINOR PHASES (gc, gcp) Leucogranites are a minor, probably late development within the northern Michelago body. These rocks appear as narrow border phases along the northeastern and northwestern boundaries, along Teatree Creek at GR 010450, and just north of the "Micaligo" road at GR 997420 respectively. Leucocratic dykes trending in a northwesterly direction to the south of "Micaligo" homestead form distinctive outcrops, which leucogranites have also been found west of Cockatoo Creek at GR 021367 and along the southeastern margin at GR 010308. The rocks are largely quartz and plagioclase (oligoclase), with very minor development of biotite and/or orthoclase in some specimens. They are generally fine to medium grained with sporadic quartz phenocrysts up to 5 mm. Possible altered clinopyroxene exists in the dyke rock south of "Micaligo" homestead. Adamellites and aplitic phases are best represented east of "Collingwood" homestead (GR 990318). The fine-grained aplites contain quartz, orthoclase, biotite, possible plagioclase, and iron ore, and appear as small hills of clustered tors, although angular !Jlocks are not uncommon. Some rocks tends to be slightly porphyritic, with coarser varieties found to the east near the boundary with the Onslow Granodiorite. Porphyritic phases are best developed north of the Tinderry road. Here large pink feldspar crystals (orthoclase), biotite, and basic inclusions, which may be up to 25 mm wide, are present in a fine-grained grey groundmass. The porphyries are possibly only dykes, but their exact nature is difficult to ascertain because of the paucity of outcrop in this area. SOUTHERN MICHELAGO BODY Although this body has some areas of biotite granite, a hornblende - biotite-rich phase, the Koolambah Adamellite, is dominant, particularly in the central, southern, and eastern areas. Minor aplitic and porphyritic rocks are also present. KooLAMBAH ADAMELLITE (gck) nov. Derivation The adamellite is named after "Koolambah" homestead at GR 020224. 95 96 Dietribution GEOLOGY OF THE MICHELAGO 1:100,000 SHEET As noted above, this is the major phase in the southern Michelago body and covers an area of approximately 26 km 2 • Type Area Mineralogical and textural variations are present within the Koolarnbah Adamellite but it is typically represented by the outcrop to the southeast of "Bundarra" homestead, at GR 031235 (appendix 2-27). Deeaription The adamellite is generally pale grey to white in colour, medium to coarse grained, and enriched in quartz, hornblende, and biotite. A typical specimen consists of quartz, plagioclase, microcline, biotite, and hornblende, as well as minor opaques (appendix 2-29). Some varieties are subporphyritic with larger plagioclase and quartz crystals, for example, at GR 024196. Alteration has taken place (appendix 2-28). Large, frequently strongly weathered tors of adamellite are the typical mode of outcrop, resulting in a fairly low topography, except close to the Ordovician boundary. Mafic-rich xenoliths ranging from 25 to 50 rom have been observed, for example, along Strike-A-Light River at GR 019221. Baczynski (1970) noted globular mafic inclusions, attaining diameters of over a metre, locally abundant along the western side. He noted also that there were no reaction rims between the hornblende rich xenoliths and the adamellite, only a sudden change of grainsize marking the boundary. The xenoliths appear to be fairly sporadic in occurrence. Chemical analyses of the adamellite are given in appendix 3. MINOR PHASES (gc, gcp) A biotite granite is particularly well developed to the west of "Bundarra" homestead at GR 018248 where a ridge of hills is composed predominantly of medium-grained massive granite. Perthitic alkali feldspar and quartz are set in a matrix of quartz, perthitic alkali feldspar, minor plagioclase (oligoclase), biotite, and rare opaques. Moderate alteration has taken place (appendix 2-29). Variations on this composition and texture exist, with biotite present as phenocrysts and minor muscovite developed in the groundrnass. Biotite granites are developed along the western margins, also in narrow bands. DEVONIAN INTRUSIONS Porphyritic phases are less common but do occur as marginal varieties, for example, at GR 018191 and GR 099238. At the latter locality, quartz, perthitic alkali feldspar, and minor plagioclase (oligoclase/andesine) are set in a matrix of perthite - quartz and plagioclase (appendix 2-30). Dykes are numerous and are predominantly aplites. A good example is at GR 013229 where a 9 m wide dyke consists of quartz, feldspars, (predominantly orthoclase) and minor plagioclase with sericite - epidote alteration. The grainsize ranges between 0.7 and 0.13 mm'and the rock is texturally holocrystalline. Dykes are well represented at the eastern and western margins of the granite, as shown in several road cuttings along the Bredbo - Jerangle road. At the eastern boundary an unusual dyke less than a metre wide penetrates the granite and sediments. Thin-section analysis reveals two rock types; one, a siltstone, is present as rounded fragments 10 x 50 mm; the second rock type would appear to be a greisen or a granitized sandy shale (appendix 2-31). A chemical analysis of a porphyry dyke at GR 015190 is given in appendix 3. SAPLING FLAT IGNEOUS COMPLEX (gs) Richardson 1975 modified from Joplin et al. 1953 Derivation The name is taken from Sapling Flat Gully which runs along the north-northwestern extremity of the granitic mass at GR 127352. Distribution The Sapling Flat Igneous Complex is restricted in outcrop to the southeastern corner of the Michelago 1:100,000 sheet area. Northern, southern, and western extremities lie at GR 139364, 116217 and 088278 respectively, with the eastern fault-bounded margin paralleling the Bredbo - Jerangle road. In areal extent the Sapling Flat Igneous Complex covers some 26.7 km 2 and forms a meridionally elongated mass of irregular width, which develops from 0.3 km near the Bredbo - Jerangle road to a maximum of 3.8 km near Jerangle and decreases northwards to 0.8 km. Synonymy and Previous Work Joplin et al. (1953) introduced the name "Sapling Flat Granite", although previous workers in the area had already noted and described portions of the mass. Raggatt (1929) first mentioned a western granite when he was mapping the Anembo gossans. Williamson (1949 unpubl.) included the northern section of the "Sapling Flat Granite" within the scope of his thesis and referred to it as the "Older" 97 98 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET granite in comparison with the "Younger" or "Jerangle Granite". Glasson (1957 unpubl.) made a brief reference to the granite and compared it to the Boro Granite to the west of Captains Flat, while Rose (1962 unpubl.) carried out field mapping on a scale of 1: 31,680 over the northern part of the granite. Usage of the name "Sapling Flat Granite" was continued by Best et al. (1964) and Brunker et al. (1971). Subsequent work by Richards (1967 unpubl.) and Slepecki (1973 unpubl.) has led to subdivisions of the mass. Description Richards (1967 unpubl.) subdivided the complex into three dominant bodies. His "Limekiln Granodiorite" roughly corresponds to the area mapped originally by Williamson (1949) and is mainly distinguished from the remainder of the Sapling Flat Igneous Complex by the presence of hornblende. The name, however is invalid as the Limekiln Group has been defined on the Bathurst 1:250,000 sheet. Consequently the name Danswell Creek Granodiorite is substituted for the name "Limekiln Granodiorite". The predominant phase is the Wangrah Adamellite which was originally defined by Richards as an adamellite of variable texture and mineralogy. Richards delineated a third phase, the "Mount View Adamellite", on the basis of the presence of xenoliths and a well-developed rapakivi texture. This name is also invalidated by the published definition of Mount View Range Granodiorite which crops out in the vicinity of Pokolbin. However, in the present work this body has been included in the Wangrah Adamellite because of their similarity in the field. Slepecki (1973 unpubl.) indicated three smaller, separate phases within the body of the Wangrah Adamellite. He delineated a porphyritic adamellite and a biotite - hornblende adamellite phase, and indicated the development of "ocellar hybrids" from the basic xenoliths. It would seem that Slepecki's porphyritic adamellite, biotite - hornblende adamellite, and "ocellar hybrid" correspond roughly to Richard's defined "Mount View Adamellite" in that all of these phases contain minor hornblende and the areas of outcrop roughly correspond. Boundary ReZationships The Sapling Flat Igneous Complex intrudes regionally metamorphosed Ordovician sediments and has truncated the meridionally trending andalusite isograd, as mapped by Slepecki (1973). The western boundary of the complex is strongly controlled by the regional structural trend as evidenced by the step-like effect in widening northwards. DEVONIAN INTRUSIONS Along the eastern boundary the Narongo Fault is the most influential structural feature for some 10.25 km. It is possible that the fault preceded the formation of the complex and influenced its emplacement, with subsequent reactivation of the fault in more recent times leading to the development of a prominent scarp. In the northern area, both Raggatt (1929) and Williamson (1949) observed gneissic foliation and outcrops of strongly cataclastic granite ~lose to the line of the Narongo Fault. Late Silurian sediments and volcanics lie adjacent to the Narongo Fault and the Sapling Flat Igneous Complex. No contact metamorphism has taken place along the faulted margins. On the northeastern boundary, the Ordovician sediments have been strongly contact metamorphosed by the complex and deformed between two branches of the Narongo Fault. Cordierite, chlorite, biotite, and pink-coloured andalusite are all developed, with the andalusite most common close to the complex sediment boundary. The pink andalusite appears as "isolated crystals" (Rose 1962, Joplin 1968) ranging up to 50 mm in length. Chiastolite is also developed in places. Along the northwestern and western margins, contact metamor- phism is not so easily defined, as the sediments have already been regionally metamorphosed to a high grade with both andalusite and cordierite present. Both acid and basic dykes have intruded the complex and surrounding sediments. In Sapling Flat Gully an epidiorite dyke trangresses both the granite and the sediments. Another dyke up to 3 m wide trends northeasterly across the mass between two arms of the Narongo Fault. This dyke is basic in composition. In the northern area, small dykes (only a few centimetres in width) intrude the sediments. They are of similar mineralogy to the granodiorite, but muscovite is developed in greater amounts than biotite. Characteristically they are even grained with an average grainsize of almost 1 mm. They reveal some flow lineation. Age A potassium - argon aCje of 325 m.y. (White 1962) has been obtained for the Sapling Flat Igneous Complex (see appendix 4), but this date appears to be of questionable accuracy (J. Richards pers. comm.). Subsequent dating (Rowley 1975) is also considered to be suspect because of the possible effect of adjacent faulting. The granite is most likely of Siluro-Devonian age with the time of its emplacement in the later stages of the Bowning Orogeny. Thus it appears to be genetically related to the Jerangle Igneous Complex. 99 100 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET DANSWELL CREEK GRANODIORITE (gsd) nov. Derivation The Danswell Creek Granodiorite is named after Danswell Creek, which lies close to the granodiorite's western margin at GR 110332. Distribution The granodiorite constitutes the northern part of the Sapling Flat Igneous Complex and is its second major phase. An area of 8 km 2 is covered by the granodiorite. Synonymy and Previous Work The granodiorite was originally defined under the invalid name of "Limekiln Granodiorite" by Richards (1967 unpubl.). Type Area No type area has been previously defined, but Richards (1967) collected a fairly representative sample from GR 120335 (appendix 3). Description The rock is generally coarse grained with a hypidiomorphic granular texture, but along the northern and northwestern margins it becomes finer grained to porphyritic with quartz and plagioclase phenocrysts. These finer rocks are possibly chilled bordervar±ants. The Danswell Creek Granodiorite consists of large bluish quartz crystals, pink K-feldspar, white plagioclase, and clusters of medium-grained biotite and hornblende (appendix 2-32). A thin section analysis by Williamson (1949) showed the rock to be composed of quartz, orthoclase, microcline including microperthite, plagioclase, biotite, apatite, and iron ore. Hornblende and muscovite may occur and also fluorite, chlorite, and other alteration products. Quartz is present as anhedral grains up to 4 mm across and also as intergrowths with microcline and microperthite; orthoclase ranges in size from 1 to 4 mm; plagioclase crystals are up to 3 mm and sometimes develop into microperthite; apatite is common in small euhedral prisms; while iron ore is present mainly as inclusions in biotite. Hornblende is frequently present in association with biotite, of which there are two varieties -- a common strongly pleochroic variety with puckered cleavages and frequent iron ore and apatite inclusions, and a less common variety which is reddish-brown in colour and has ferromagnesian clots and occasional pleochroic haloes. DEVONIAN INTRUSIONS A chemical analysis of the granodiorite is included in appendix 3. The granodiorite commonly crops out as massive rounded grey boulders. Along the western boundary, small fine-grained granodiorite bodies are separated by metasediments from the main intrusion. Xenoliths up to 40 cm 2 in size are especially common towards the margins and appear to be sedimentary in origin, i.e., biotite schists. Williamson (1949) described one xenolith as having a fine-grained outer zone containing quartz, biotite, and muscovite, and a leucocratic inner zone of muscovite, quartz, and feldspar, with minor iron ore and biotite. The xenoliths only appear towards the margin of the granodiorite and are of similar composition to the intervening sediments. ~NGRAH ADAMELLITE (gsw) nov. after Richards 1967 unpubl. Derivation Richards (1967 unpubl.) named the adamellite after Wangrah Trig. Station (1326 m) at GR 105259. Di8tribution The Wangrah Adamellite forms the southern and central portions of the Sapling Flat Igneous Complex. It is the more extensive ~hase in the Sapling Flat Igneous Complex and covers some 17 km . TYpe Area Within the original definition of Richards (1967 unpubl.) no type locality for the Wangrah Adamellite was included. Ho\~ever, the adamellite is adequately represented at GR 112253 where large pink tors crop out in clusters. De8oription In outcrop the adamellite forms rounded boulders which are white, yellow, orange, red, or crimson depending on the degree of weathering. Weathering is deep and in its final stage yields a white, quartz-rich residual devoid of any mafics. Portions of the Wangrah Adamellite body are also present within the limits of the Danswell Creek Granodiorite but are easily detected by differences in weathering characteristics. Richards (1967) considered the textural and mineralogical variation to be great, with textures varying from coarse to fine to porphyritic over a small area. There seems to be no apparent relationship between texture and position within the intrusion, 101 102 ---------------------------- - --- GEOUX;Y OF THE HICHE.LA~ 1:100,000 SHEET as coarse-grained margins may grade into a fine-grained interior. Slepecki (1973) noted the hypidiomorphic nature of the texture. In spite of textural differences, the mass is mapped as one unit on the basis of the absence of hornblende. presence of rare muscovite, weathering characteristics and outcrop pattern, and the comparative lack of xenoliths. Some xenoliths similar to those of the Danswell Creek Granodiorite have been found along the western margin of the Wangrah Adarlellite (photo 9). Photo 9. A partly digested chevron-folded sedimentary fragment in the Sapling Flat Igneous Complex at GR 099298 Mineralogically, the rock is a biotite adamellite as it contains quartz, f:-feldspar (which is generally microcline) , plagioclase, biotite, ar.d very rare muscovite (appendix 2-33). A chemical analysis is included in appendix 3. mllllllllllllllmfm~1111II 0004941950 DEVONIAN INTRUSIONS Both Richards (1967) and Slepecki (1973) indicated the presence of porphyritic varieties within the Wangrah Adamellite. The porphyritic adamellite outcropping at GR 114253 and GR122272 is similar to the biotite adamellite in hand specimen except for' the presence of up to 2 per cent green hornblende and the development of a rapakivi texture. Large phenocrysts of perthitic microcline up to 2 mm in size are mantled by a rim of plagioclase of maximum width 2 mm and frequently containing quartz inclusions with a myrmekitic texture. In proximity to the porphyritic variety a hornblende biotite adamellite phase is developed at GR 115273. This phase contains a little less green hornblende than the former but has a much higher plagioclase content. Xenoliths are very common, occupying up to 50 per cent of the rock. The xenoliths are fine-grained basic igneous rocks containing clinopyroxene and plagioclase and are rich in green to brown amphiboles. Texture is subpoikilitic to poikilitic and the xenoliths are in various stages of hybridization and recrystallization. Slepecki (1973) related the basic xenoliths of the hornblende biotite phase to numerous doleritic dykes intruding the country rocks and suggested that the dykes preceded the granite and contaminated the original acid magma. The third phase is an ocellar hybrid variety of the Wangrah Adamellite. It is characterized by numerous rounded quartz phenocrysts from 2 mm to 3 mm in size and surrounded by a small rim of green hornblende crystals. These ocelli possibly formed by a metasomatic alteration of basic rocks by the acid fluids. This phase is represented at GR 113250. None of these phases are indieated on the Michelago 1:100,000 sheet. Joint patterns are similar within the Wangrah Adamellite and the Danswell Creek Granodiorite, i.e., 90° dip/090° dip direction, 90°/135°, and 90°/250°, with the first best developed. Within the minor phases, 90%60°, 90°/135°, and 50%80° are dominant. Analysis by Rose (1962) of some 150 joint strike readings indicated three major trends of 010, 030, and 090° T and two minor trends of 150° and 055° T. OTHER IGNEOUS BODIES BREDBO RiVER ADAMELLITE (gr) Richardson 1975 Derivation The name Bredbo River Adamellite has been taken from the Bredbo River which traverses the mass. 103 11111111/11111111111111/1/1 /1/11 11111/1111111111111111111111 0004941960 104 Distribution GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Lying roughly 1.5 km to the west of the Jerangle Igneous Complex, the adamellite is a small, previously unmapped body cropping out near the Bredbo River. It extends from GR llH180 southward to GR 120135 on the Michelago 1:100,000 sheet area. Covering an area of some 2.5 km 2 , the adamellite has an extremely elongate form approximately 5 kID long by 0.75 km wide. Type Area Best exposure of the adamellite appears to be along the riverbanks and in the river bed at GR 115165. Despite a certain degree of alteration, it is fairly distinctive in outcrop here. Description Boulders ranging up to 1.5 m in diameter form the characteristic type of outcrop. This rock weathers to a coarse siliceous soil which supports a typical dry sclerophyll forest, now mainly cleared for farming and grazing purposes. Deep widespread weathering results in the sporadic appearance of boulders but only along ridges and in the river bed. To the north of the Bredbo River the topography becomes more rugged and the adamellite appears as more massive, less weathered outcrop. The adamellite consists of two phases, with the dominant one well represented along the river at GR 118166. This phase is a medium to coarse-grained adamellite containing large pink subhedral crystals of microperthitic alkali feldspar (30 per cent), 25 per cent quartz, 20 per cent plagioclase, and biotite, with minor inclusions of muscovite, apatite, magnetite, and zircon, (appendix 2-34). The second and minor phase forms very weathered large tors at GR 115160. It is texturally heterogeneous, with large white feldspars and slightly smaller quartz crystals set in a fine-grained biotite-rich groundmass. Thin-section analysis shows the rock to be a porphyritic adamellite containing quartz (15 per cent), plagioclase (15 per cent), and perthitic alkali feldspar (10 percent), in a polygonal matrix of biotite, quartz, plagioclase, microcline, apatite, and zircon (appendix 2-35). Mild alteration has caused the formation of sericite, calcite, and chlorite in both phases, in addition to epidote in the major phase. A few xenoliths have been noticed within the dominant adamellite phase but are small and generally less than 30 mm wide. One xenolith collected at GR 117167 was found to be a granitized sediment with possible relict bedding. It consists of fine to coarse-grained granoblastic quartz, biotite, muscovite, alkali feldspar, and plagioclase, with minor apatite and opaques (appendix 2-36). DEVONIAN INTRUSIONS Boundary Relationships Much of the eastern side of the adamellite is fault bounded, with a band of Silurian volcanics and sediments adjacent to the adamellite. Apart from this contact, the mass invades Late Ordovician metasediments which separate it from the Jerangle Igneous Complex to the east. A minor fault displaces the southern section of the mass by 100 m and other faulting possibly takes place further south. No contact metamorphism aureole has been noted. Age No age dating has been carried out on the adamellite but it is considered to be of similar age to the Jerangle Igneous Complex, i.e., Siluro - Devonian. TINDERRY GRANITE (gt) Joplin et al. 1953 Derivation 105 The name of the granite is derived from Tinderry Trig. Station (1618 m) at GR 054470. Distribution The granite is located approximately halfway between Michelago and Captains Flat, with the main mass of the body cropping out north of, but extending across, the Michelago - Tinderry road around GR 050420. To the west, the Michelago Igneous Complex is only 2 km distant, while to the north, only some 2 km separate the Tinderry Granite from the Watch Box Granite. In size, the granite covers some 37 km 2 ; it is elongated meridionally over a distance of 12.5 km, and is 3.5 km wide. Synonymy and PJ.·evious Work Brown (1928 unpubl.) was the originator of the name, which was perpetuated by all subsequent authors. Joplin et al. (1953), however, were the first to publish the name. Type Area No type area has been described but the granite is well represented along the Tinderry road which traverses it near its southern extremity (GR 042420 to GR 057422). Desoription In outcrop the granite is a massive well-jointed body, and, in comparison to many of the other granitic bodies, quite resistant to weathering. Large rugged granite peaks form the 106 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Tinderry Range, a topographic feature which dominates the central area of the Michelago 1:100,000 sheet (photo 10, figure 31. Thp joint pattern is characterized by north - south, east - west directions with less well developed joints trending northwesterly and northeasterly. These last two are associated with faults and major lineaments affecting the area. Photo 10. View of the Tinderry Granite, the Foxlow Beds, and the Michelago Igneous Complex. The Tinderry Granite forms rugged peaks in the background, with the Foxlow Beds cropping out on the lower slopes. The Michelago Igneous Complex, by contrast, forms a topographic low with relatively poor outcrop in the foreground. The view is taken frOlll the Michelago - Tinderry road looking towards the east mill "III[II /III fill III ~II 0004941970 DEVONIAN INTRUSIONS 107 Compositionally, the granite is a massive, mainly medium to fine-grained biotite granite. One specimen collected near the southern tip of the body was found to contain 30 per cent quartz, 45 per cent alkali feldspar, 15 per cent plagioclase, 5 per cent biotite, and rare zircon (appendix 2-37). Minor amounts of an adamellite porphyry type phase have been noted (appendix 2-38). Apart from the margins, where some sedimentary type xenoliths have resulted from the granite's intrusion into the Ordovician rocks, xenoliths are generally absent from the Tinderry Granite. Chemical analyses of the granite are given in appendix 3. Boundary ReZationships Ordovician sediments entirely surround the granite, the boundary of the granite running parallel to the regional strike. The actual boundary is very distinctive and in outcrop forms a zig-zag pattern due to the moderate outward dip of the granite sediment contact. Contact metamorphism is not highly developed and is probably masked in part by the metamorphic grade of the surrounding sediments. Fine-grained cordieri te - bioti te hornfelses have been observed in its vicinity, for example, at GR 073475 (appendix 2-4). The metamorphic grade reaches the hornblende hornfels facies. It appears to be a continuation of the Watch Box Granite from which it is separated by 2 km of sediments. Age Potassium - argon age dating of biotite (Evernden and Richards 1962) gave an age of 378 m.y. (appendix 4). However, J. Richards (pers. corom.) now considers this to be too young. This body is regarded as having a similar age to the Harrisons Peak, Urialla, and Watch Box Granites, i.e., Early Devonian. HARRISONS PEAK GRANITE (gh) Joplin et al. 1953 after Veevers 1951 unpubl. Derivation The Harrisons Peak Granite is named after Harrisons Peak (1173 m) at GR 194613. Distribution The granite lies some 4 km northwest of the township of Captains Flat; easy access is provided by a road which crosses the body. It crops out over an area of some 3.8 km 2 , and is a small meridionally elongated stock, measuring 3.2 km in length by 1.2 km wide. //111//1/11/111//11///1/1/1/1///1/11///1/1/1//1////111////1/ 0004941980 108 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Synonymy and Previous Work Browne (1950) first made passing reference to the granite, followed by Veevers (1951 uhpubl.) who named the mass the "Harrisons Peak Massive Microcline Granite" and briefly described it. First published on the Canberra 1:250,000 Geological Sheet, 1st edn, (Joplin et al. 1953) the name Harrisons Peak Granite was subsequently used by Oldershaw (1965), Glasson (1957 unpubl.), Strusz (1971), and others. Type Area Although previous literature has not indicated a type area, the granite is probably best represented at GR 195613 in the vicinity of Harrisons Peak. Desoription The Harrisons Peak Granite is a homogeneous, non-foliated, medium-grained, massive biotite granite with a predominantly hypidiomorphic granular texture. Grey in colour, the granite contains quartz, microcline, plagioclase, biotite, and chlorite. The quartz crystals are generally smaller than the Inicrocline crystals, which may be between 3 mm and 6 mm long. Plagioclase and microcline are present in equal proportions and are frequently sericitized, while biotite is often partially altered to chlorite. No veins of pegmatite, aplite, greisen, or quartz have been observed in the granite. Boundary Relationships Ordovician sediments surround the granite but rocks of Silurian age lie only a few kilometres to the east. The granite has intruded the country rock in an elongated form parallel to the regional strike. Contact metamorphic effects are negligible and only a slight baking of the already regionally metamorphosed sediments has taken place. Glasson (1957) observed some lit-par-lit injection along the southern extremity of the granite contact. The fact that the granite contains microcline and that it contains no pegmatite veins, vughs, or any form of mineralization, is indicative of a low temperature of intrusion. Some 9.5 km separate the Harrisons Peak Granite from the Watch Box Granite. Both granites are identical in composition and are possibly genetically related. The granite may also be related to the Boro Granite to the east of Captains Flat. DEVONIAN INTRUSIONS Age Both Veevers (1951) and Oldershaw (1965) have suggested that the granite was emplaced in the late stages of the Bowning Orogeny, in contrast with Browne's (1950) Kanimblan age. It is thought to have a similar age to the Urialla, Tinderry, and Watch Box Granites (Early Devonian). URIALLA GRANITE (gu) Richardson 1975 modified from Joplin et al. 1953 Derivation 109 The Urialla Granite derives its name from Urialla Trig. Station at GR 043606. Distribution Lying to the east of the "Burra"-Michelago road, the Urialla Granite is one of several bodies cropping out in the vicinity of the Queanbeyan River. The mass is elongated in a north - south direction over a distance of some 11 km. It has an average width of 2.5 km and covers some 17 km 2 • It lies roughly parallel to the Watch Box Granite to the east. The "Burra" - "Urila" road crosses both granites. Synonymy and Previous Work Two distinct bodies, separated by a very narrow belt of Ordovician sediments, were first described and mapped by Veevers (1951 unpubl.) who named them the "Urialla Massive Microcline Granite" and the "Urialla Foliated Granite". In all published works (~oplin et al. 1953, Best et al. 1964, and Strusz 1971) both of the granites are referred to as the "Urialla Granite". The present author has chosen to retain the name only for the western body, Veevers' "Urialla Foliated Granite". Type Area No type area has previously been defined, but the granite is well represented in the vicinity of the Urialla Trig. Station, where both porphyritic and fine-grained varieties appear. Description This granite would appear to be divisible into several phases, with coarse porphyritic varieties developed particularly along the western margin. Fine to medium-grained spheroidal boulders of a biotite granite composition have been found at GR 054630 and at Urialla Trig. Station (GR 043606). Microcline, quartz, oligoclase, and biotite are the most common minerals within the fine-grained biotite granite which forms most of the body 110 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET (appendix 2-39). The minor granodioritic phase contains plagioclase (olioclase - andesine), quartz, biotite, and opaques ranging in grainsize between 0.5 and 3 rom, in a dominantly feldspar groundmass (appendix 2-40). Xenoliths up to 220 rom in length are found along the margins of the body in the porphyry phase and reveal varying stages of absorption by the porphyry. Porphyritic stringers invade the country rock at several places to the west, as is evident along the "Urila" road. One specimen at GR 030617 contains phenocrysts of plagioclase (andesine), quartz, alkali feldspar, and granular epidote completely replacing biotite. In composition it approximates to an adamellite (appendix 2-41). A foliation with a vertical dip was originally thought by Veevers (1951) to be developed throughout the granite, with a trend parallel to the eastern and western granite margins. However, the bulk of the Urialla Granite, i.e., the fine-grained biotite granite, appears to have no foliation and it is only in the marginal porphyritic phases that a groundmass foliation is developed. A chemical analysis of the major phase is included in appendix 3. Boundary ReU2tionships The southern and northern boundaries of the granite are indistinct and the present ground surface would seem to be coincident with the roof of the granite in these parts. Contact metamorphism is evident, with sediments raised to the biotite facies on the western contact (a width of 1.5 km) and a metaquartzite developed on the eastern margin. Ordovician sediments completely surround the granite, separating it from the Watch Box Granite to the east by a minimum distance of 180 m. Age No age dating has been carried out on the granite but it is probably of similar age to the Harrisons Peak, Watch Box, and Tinderry Granites. Veevers (1951) believed that it was emplaced before the Watch Box Granite but offered no evidence for this conclusion. Generally, then, the granite is thought to be of Early Devonian age (Brunker et al. 1971), although Best et al. (1964) suggested a Siluro - Devonian age. WATCH BOx GRANITE (gw) Richardson 1975 DeI'ivation Watch Box Creek, which joins the Queanbeyan River at GR 093635, is the source of the granite's name. DEVONIAN INTRUSIONS Distribution This granite, like the Urialla Granite, is located to the east of Burra near the northern end of the Michelago 1:100,000 sheet area. It is crossed by the "Burra" - "Urila" road. The Watch Box Granite crops out over an area of some 12 km 2 , from GR 092653 to GR07l555, and has an average width of 1.2 km. Synonymy and Previous Work 111 Veevers (1951 unpubl.) was the first to map and describe the granite, calling it the "Urialla Massive Microcline Granite". Subsequent authors (Joplin et al. 1953, Best et al. 1964, and Strusz 1971) referred to the Urialla Granite and the Watch Box Granite under the single name of the "Urialla Granite". Type Area Good outcrop of the granite occurs immediately to the south of the "Burra" - "Urila" road at GR 089612. Desoription In outcrop the granite typically forms spheroidal boulders and massive jointed blocks, which result in a rugged terrain. It is a ma'ssive granite with a fine to medium-grained hypidiomorphic granular texture. Biotite, quartz, microcline, and plagioclase are the primary minerals, with minor inclusions of apatite and opaques (appendix 2-42). Microgranite containing muscovite is developed in places along the margins, for example, at GR 087603 (appendix 2-43). No xenoliths are present within the mass. Minor flakes of molybdenum are found at GR 086600 in the granite (L. Barron pers. comm.). Boundary ReZationships The granite is entirely surrounded by Late Ordovician sediments, the mass being concordant with the strike of the country rock. Along its northern limit the igneous rocks show intimate mixing with the sediments, but elsewhere contact metamorphism is barely evident. The northeastern boundary forms the bed of the Queanbeyan River. The Tinderry Granite, which appears to be a continuation of the Watch Box Granite, lies directly to the south, separated from it by 2 km of sediments. The Watch Box Granite is identical in composition with the Harrisons Peak Granite. The Urialla and Watch Box Granites lie roughly parallel to one another and are of similar shape. 112 Age GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The Watch Box Granite is though to have been emplaced contemporaneously with the other small granitic bodies in the area i.e., at the commencement of the Devonian period. GOOD GOOD ADAMELLITE (gg) Richardson 1975 Derivation "Good Good" homestead (GR 098212) is the source of the name. Dietribution The Good Good Adamellite consists of two small bodies which crops out at the head of a tributary creek of Ryans (Wangrah) Creek at approximately GR 088236. Surrounded by Ordovician metasediments, the small granitic bodies lie 1.6 km west of the Sapling Flat Igneous Complex and 3.2 km east of the southern body of the Michelago Igneous Complex. The larger western body covers some 0.27 km2 and the eastern body some 0.08 krrf. Synonymy and Pl'evioue Work Richards (1967 unpubl.) first noted the two small granitic intrusions and considered them to be pneumatolyzed stages of the Wangrah Adamellite. Slepecki (1973 unpubl.) remapped these bodies and described them as tourmaline granites. Type Area The adamellite is well exposed near the creek (GR 087238). Deeaription The Good Good Adamellite is a medium-grained adamellite consisting of microperthite, plagioclase, quartz, abundant tourmaline (schorlite variety), and minor muscovite. No biotite has been noted. Boundary Relationehipe Late Ordovician sediments completely surround the adamellite. Age The Good Good Adamellite was probably synchronous with the Sapling Flat Igneous Complex, and therefore has a Siluro - Devonian age. MINOR AcID TO INTERMEDIATE INTRUSIONS (g) INCLUDING UNNAMED SMALL PORPHYRIES (S-D) Close to the old "London Bridge" homestead, at GR 042664 and GR 047663, small bodies of porphyry intrude the sediments and tuffs of the Cappanana Formation and the Colinton Volcanics. Veevers (1951 unpubl.) introduced the name "London Bridge Massive Quartz Porphyry" for these quartz- feldspar porphyries. Vallance (1966, p. 58), after close examination of the area, described the rock as DEVONIAN INTRUSIONS 113 "characteristically porphyritic in quartz, feldspar and, less often, biotite. Quartz phenocrysts up to 4mm in diameter tend to be euhedral where not resorbed. Compared with the strained phenocrysts in the '" [Colinton Volcanics] the quartz here is relatively untouched by deformation though some exhibits undulose extinction. The feldspar phenocrysts, typically subhedral and as much as 3 mm across, are extensively altered to clays. Some appear to be oligoclase, others are too altered to allow of sure identification. A few biotite phenocrysts (3 mm) occur but most of the biotite, which never seems to exceed 10% of the rock, appear as small flakes in the base. Much of it is altered to green chlorite but where original mica has been preserved it is strongly pleochroic from light yellow to dark green. Apart from minor opaque phases, biotite represents the sole primary dark mineral. The fine-grained groundmass contains quartz and subordinate altered feldspar as well as scattered biotite. Some examples show micrographic quartz-feldspar intergrowths in the groundmass". Vallance noted changes in the porphyry's character where it has assimilated calcareous sediments, for example, considerable reduction in quartz content and disappearance of biotite. Similar intrusive adamellite porphyry dykes are present along the "Burra" - "Urila" road but these have been described with the Urialla Granite. The porphyries at London Bridge are probably related to the Urialla Granite. About 1 km southwest of Gigerline Trig. Station (GR 900672) a small body of granitic porphyry intrudes sediments and tuffs of the Bransby Beds (appendix 2-44). A shear zone of the Murrumbidgee Fault truncates and passes along the northeastern boundary of the porphyry. As the porphyry intrudes Late Silurian to earliest Devonian units, its maximum possible age is Early Devonian. Minor leucogranitic bodies lie at sporadic intervals between the Michelago - "Burra" road andthe Tinderry and Urialla Granites, for example, at GR 015558 and GR 028590. The leucogranites, which are dyke-like in form, are usually about 100 m wide. Generally fine grained, the rock is weathered and partially ironstained. Quartz dominates, and minor whitish feldspar and very minor mafics (biotite) are present. Some minor porphyritic rocks with quartz and feldspar phenocrysts are associated with the outcrop at GR 015558. The bodies are completely surrounded by Late Ordovician metasediments. Another minor leucogranite was noted by Slepecki (1973) at GR 098223 as a fine-grained aplitic rock consisting essentially of perthitic microcline, quartz, plagioclase, and minor muscovite. Of limited extent, it is most likely a dyke related to the Sapling Flat Igneous Complex. At various locations throughout the area, minor dykes have been noted: for example, in Primrose Valley, at GR 138576 (adamellite porphyry) and at GR 133572 (microgranodiorite porphyry); near "Norongo" at GR 176457 (granite porphyry); and further north at GR 174490 (granite subporphyry) (appendix 2-45,46,47,48). Worthy of note is a small body, possibly a dyke, of mildly altered hornblende biotite granodiorite present at GR 012273, to the north of the Koolambah Adamellite. 114 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Rocky Pic Anticlinorium JERANGLE IGNEOUS COMPLEX (gj, gjt, gja) modified from Joplin et al. 1953 Derivation The name of the Jerangle Igneous Complex is derived from the village of Jerangle at GR 130278. Distribution The Jerangle Igneous Complex is the western septum of the Bega Batholith which extends meridionally over some 300 km from Lake George in New South Wales to Cape Everard in Victoria. Within the Michelago 1:100,000 sheet area, the northern extremity of the complex is at GR 192464, with the granite widening to a maximum of 13 km near Blue Bull Peak (GR 142211). The complex covers some 295 km 2 on the Michelago 1:100,000 sheet. Synonymy and Previous Work Early literature makes reference to the "Jerang~e Grey Granite" (Baker 1915), a "western granite" (Raggatt 1929), a "younger granite" (Williamson 1949 unpubl.) and the "Anembo Granite" (Whitten 1952) but only brief descriptions were provided. The name "Jerangle Granite" was introduced by Joplin et al. (1953) and subsequently used by Rose (1962 unpubl.) and Richards (1967 unpubl.). Best et al. (1964) modified the name to "Jerangle Granite Complex" and this was later used by Brunker et al. (1971) and by Strusz (1971). Desoription Two major phases, both possessing textural and mineralogical variants, are recognized within the Jerangle Igneous Complex. These are the Anembo Granodiorite and the Towneys Creek Adamellite. Subdivisions within the granite were recognized as early as 1915, when Baker identified an even-grained "red" granite and a coarse "grey" granite, both with porphyritic variants. Raggatt (1929) noted a very fine-grained phase along part of the western margin and ~his was further described by Williamson (1949 unpubl.). Two major phases are indicated on the Canberra 1:250,000 Geological Sheet 2nd edn (Best et al. 1964) - a biotite hornblende "granite" with acid and basic dykes, and a biotite "granite", with aplite, porphyritic aplite, acid, and basic dykes. Richards 1967 unpubl.) made a similar subdivision with his description of the "Round Hill Granodiorite" and the Towneys Creek Adamellite , the former name being invalidated, however, by the published name Round Hill Group. Boundary ReLationships DEVONIAN INTRUSIONS 115 Regionally metamorphosed Ordovician sediments have been intruded by the complex but have also been partially faulted against it by the Narongo Fault. Silurian volcanics and sediments have been disrupted by movement along the same fault, with the result that in the junction between the Anembo and Narongo Faults, Silurian rocks are in faulted contact with the complex. In the vicinity of Jerangle, a Tertiary basalt flow has covered the western margin, with subsequent erosion leaving a northwest-trending basalt ridge and two small hill caps. Numerous west-northwest-trending basic dykes have intruded the Jerangle Igneous Complex along lines of weakness, and subsequent lateral movement along some of these lines has led to displacement and partial rotation of the body. This is aptly demonstrated by the rotation of the basic dykes to a northwesterly direction to the north of the Anembo Fault. Contact metamorphism is best developed along the southwestern boundary, especially south of the Bredbo River. At GR 135145 a progression from granite to g~anitized and contact metamorphosed sediments to yellow-brown siltstones takes place over some 50 m. Thin-section analysis reveals the rocks to be metagreywackes and subporphyritic granitic rocks (appendix 2-49). The width of the contact zone decreases northwards and is not well developed north of the Bold Slate Range Fault. However, Whitten (1952, p. 19) described the contact rock in the vicinity of the junction of the Anembo and Narongo Faults as being a "thinly bedded silicified shale, well sheared and complexly folded. Occasionally, a sandstone band contacts the granite when it may become difficult to distinguish the silicified sandstone from the finer grained aplitic phase of the granite itself". Along the northern and western margins, sediments generally show very little effect of contact metamorphism, indicating the complex's low temperature of intrusion. However, one exception noted by Williamson (1949) is along Adjenbilly Creek, where a psammite shows partial greisenization. The presence of contact metamorphism could also be disguised by the high grade of regional metamorphism. The latter would seem to be the controlling factor where knotted schists have been found close to the complex/sediment boundary in the vicinity of Slapup (Araluen 1:100,000 sheet). T~ere is very little evidence available to clarify the relationship between the Anembo Granodiorite and Towneys Creek Adamellite. Direct contact between them is minimal and, although the relative shapes of the boundaries suggest that the granodiorite body is the younger, a specimen collected from GR 192335 reveals a fragment of hornblende granodiorite caught up in a biotite adamellite, thus suggesting that the latter is the younger. 116 Age GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Potassium - argon dating of bioti tes (White 1962, Richards 1967) has given an age of 393 m.y., since revised to 396 m.y. (J. Richards, pers. comm.) (See appendix 4). This date suggests a Siluro - Devonian time of intrusion, i.e., one related to the Bowning Orogeny. Evidence for this age cannot be substantiated by direct contact between the Silurian sediments and volcanics and the complex, at least not in the Michelago 1:100,000 sheet area. ANEMBO GRANODIORITE (gja) nov. Derivation The Anernbo Granodiorite is named after the village of Anembo at GR 195347 on the Jerangle - Captains Flat road. Distribution The Anernbo Granodiorite is the major phase of the Jerangle Igneous Complex. It occupies two-thirds of the total outcrop, appearing along the eastern side of the mass for its full length, except for a minor isolated mass west of Blue Bull Peak (GR 142211). Lateral displacement of the granodiorite's boundary with the Towneys Creek Adamellite has taken place along several northwest-trending faults. The Anembo Granodiorite covers approximately 220 km 2 on the Michelago 1:100,000 sheet. Type Area The type area for the granodiorite is located at GR 191335, a short distance to the south of Anernbo, where large rounded boulders have been freshly exposed by new road works. Description Good outcrops are also seen along the Jerangle - Peak View road around GR 165165, where the granodiorite has the typical tor shape and exfoliation mode of weathering. These boulders, which may be up to 3 m in diameter, dot the undulating countryside in small clusters. They are a characteristic grey to creamy colour. The phase is a texturally homogeneous, coarse-grained, xenolith- enriched biotite - hornblende granodiorite. It has a coarse, hypidiomorphic granular texture, except for a small, fine-grained zone around GR 218422. Williamson (1949) described the granodiorite as being usually light grey or creamy, with biotite and hornblende as the dark ferromagnesian minerals. Plagioclase (andesine) is commonly zoned, fairly heavily saussuritized, and in excess of orthoclase, which is DEVONIAN INTRUSIONS partly kaolinized. Biotite is pheochroic and frequently partly chloritized. Hornblende is less abundant than biotite, usually subhedral, and shows simple twinning. Epidote and apatite are also noted. 117 Richards (1967) described the granodiorite as being predominantly white in colour with large patches of clear, irregularly shaped quartz crystals, white feldspar, biotite, and well-developed prisms of hornblende up to 20 mm in length. Thin-section analysis (appendix 2-50) shows a typical specimen of the granodiorite to contain 30 per cent quartz, 25 per cent plagioclase, 10 per cent microcline, 5 per cent hornblende, and 10 per cent biotite. Xenoliths up to 20 cm 2 in area are common. At one locality near Anembo (GR 180335) fresh exposures of the granodiorite reveal xenoliths varying from the more typical rounded, ellipsoidal shape to an elongate form. Xenolith size falls mainly into the range between 20 x 50 mm and 120 x 150 mm hut one specimen measured 380 x 150 mm. Some of the xenoliths appear to be of sedimentary origin, possibly remnants of a roof pendant, but the majority are of igneous origin, being fine to medium grained, dark in colour, rich in hornblende, and having ra~e quartz and feldspar porphyroblasts (appendix 2-51). Typically, the xenoliths have rounded, sharp outlines, with a few having a reaction rim of K-feldspar, 20 or 30 mm wide. As described by Richards (1967), the xenolith texture consists of large, irregular quartz crystals (5 to 10 mm) poikilitically enclosing euhedral crystals of plagioclase, biotite, and hornblende with an average grainsize of 0.5 mm. Accessory minerals are fairly abundant. Replacement of primary minerals has taken place to an advanced degree, and epidote, chlorite and pumpellyite are common. With an average 18 per cent quartz content, the xenoliths approximate to a biotite or hornblende diorite. Small patches of finer grained mafic minerals are also common, but these lack sharp margins and possibly represent an advanced stage in the assimilation of xenoliths. Chemical analyses of the granodiorite and one xenolith are given in appendix 3. Richards (1967) considered the joint pattern distinctive, with vertical dips at 108 0 and 188 0 strike directions to the south of the Anembo Fault and vertical dips at 138 0 and 218 0 strike directions to the north of the fault. TOWNEYS CREEK ADAMELLITE (gjt) nov. after Richards 1967 unpubl. Derivation The Towneys Creek Adamellite, which forms the western third of the Jerangle Igneous Complex, is named after Towneys Creek, which 118 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET is crossed by the Jerangle -Captains Flat road at GR 165295. Distribution Basically the Towneys Creek Adamellite has a meridionally trending boundary relationship with the Anembo Granodiorite, and in the Michelago 1:100,000 sheet area extends from GR 140134 to GR 213444. The adamellite crops out over an area of 75 km 2 on the Michelago 1:100,000 sheet. PPevious Work The central part of the body was described by Richards (1967 unpubl.). Type Area Good representation of the adamellite is found at GR 188389, at the intersection of the Tinderry road and the Jerangle -Captains Flat road. Description As noted by Ric~~rds (1967), the intrusion is texturally heterogeneous with fine to coarse-grained to porphyritic varieties present. It has a similar mode of outcrop to the Anembo Granodiorite, with small clusters of reddish tors dotting an undulating landscape. Areas of no outcrop generally seem to separate the two major phases. Baker (1915, p. 32) was the first to describe the granite as "an even grained rock containing equal proportions of red orthoclase and quartz, similar to the Braidwood red granite". He also described a porphyritic variety containing numerous large crystals. Quartz, K-feldspar, plagioclase, and biotite with accessory opaques, apatite, and zircon are the typical minerals. Thin-section analysis by Williamson (1949) shows quartz with some slight strain and numerous tiny inclusions. Orthoclase, which is more common than plagioclase, is partly kaolinized and often occurs as microperthite, a result of exsolution. Plagioclase is usually oligoclase, and shows albite twinning. Biotite is strongly pleochroic and sometimes partly chloritized. Rare apatite and sphene are present as small euhedral crystals, while iron ore is present mainly as inclusions in biotite. Appendix 2-52 gives a thin-section analysis and appendix 3 a chemical analysis. Marginal aplitic phases are included with the description of the Towneys Creek Adamellite. These aplites are developed mainly along the western boundary of the Jerangle Igneous Complex and as dykes within the adamellite, with typical oucrops at GR 170345 and GR 159394 on the Queanbeyan River adjacent to the Anembo and Narongo DEVONIAN INTRUSIONS Faults, and at GR 135147, south of the Bredbo River. 119 They generally are of white or pink colouration with little or no ferromagnesian minerals evident. Williamson (1949, p. 52) analysed a specimen from the western margin on Adjenbilly Creek and found it to be "mainly quartz and kaolinized orthoclase, and ranges in grainsize up to 1 rom. The quartz is sometimes rather vermicular and intergrown with microperthite and orthoclase. Plagioclase is an acid variety and is usually saussuritized". Some mU3covite and sericite were also noted. No xenoliths are present. Joint pattern analysis by Richards (1967) showed strikes of 150 0 (steep easterly dip), 200 0 (dip vertical), and 170 0 (dip 50 0 east) . BORa GRANITE (go) Garretty 1937 Derivation The name Boro Granite is derived from the village of Boro at GR 425076 on the Braidwood 1:100,000 sheet. Distribution The Boro Granite -- a northern extension of the Bega Batholith, extends southward from north of Lake Bathurst, but on the Michelago 1:100,000 sheet it is only represented by its western extremities, northeast of Captains Flat. Only some 15.5 km 2 crop out in the Michelago 1:100,000 sheet area but, as noted by Oldershaw (1965), the mass crops out over an area of at least 130 km 2 along the crest of the Great Dividing Range. Synonymy and Previous Work Garretty (1937) introduced the name Boro Granite and this term was used by most successive authors (Joplin et al. 1953, Strusz 1971, and White 1962 unpubl., to name a few). However, Williamson (1949 unpubl.) referred to the granite as one of the "Older Granites", Glasson (1957 unpubl.) introduced the name "Rocky Pic Granite'; and Oldershaw (1965) the name "Rocky Peak Granite". All other names are invalidated by the earlier publication of Garretty's term. Type Area No type area for the granite has been previously defined, but the unit has been described in more detail by Felton and Huleatt (1977) . 120 Description GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The Boro Granite is described as a massive, unfoliated hornblende - biotite granite, ranging in composition from adamellite to granodiorite (Felton and Huleatt 1977). Grainsize varies between medium and coarse. Oldershaw (1965) described the mass towards the western margin, near Captains Flat, as being composed mainly of a coarse-grained biotite - oligoclase - microcline granite with feldspar crystals up to 12 mm across. He noted that towards the western margin the proportion of microcline decreases and the rock grades into a medium-grained granodiorite. Foliation is well marked in the marginal zone with xenoliths, biotite flakes, and hornblende crystals having a vertical orientation parallel to the contact. A chemical analysis is given in appendix 3. Oldershaw (1965) also noted that small pods of medium-grained hornblende diorite grading into amphibolite crop out along the western margin of the granite and possibly represent a contaminated marginal phase of the granite. Randomly scattered xenoliths are present throughout the Boro Granite, being both igneous and sedimentary in nature, ranging in size from 50 to 150 mm, and generally possessing sharp contacts with the granite. Numerous dykes invade the granite, varying from doleritic to leucocratic and porphyritic in nature. For a more detailed description, the reader is referred to Felton and Huleatt (1977). Boundary Relationships The boundary relationships of the granite are variable. On its eastern side it is truncated by the Shoalhaven Fault, to the north and west it intrudes Ordovician and Silurian sediments, west of Braidwood it intrudes Silurian acid volcanics and along its northwestern boundary it intrudes the "Lockhart igneous complex". Age Potassium - argon isotope dating on biotite from a specimen collected 16 km east of Captains Flat (Araluen 1:100,000 sheet) gave an age of 390 m.y. (Evernden and Richards 1962), suggesting that the granite was emplaced in the earliest Devonian times (see appendix 4). PERMIAN(?) Gravel outcrops (Pg) of limited extent occur in the vicinity of Captains Flat. At Mount Bollard they were recorded and described by Oldershaw (1965), who suggested a possible Permian age. The coarse river gravels at GR 224535, around the foot of Mount Bollard in the upper part of the Molonglo Valley, are about 975 m above sea level. They consist of rounded and sUbrounded cobbles of quartz and quartzite, up to 160 rom across, set in a sandy matrix. A similar gravel caps the low hills along the southern side of Yandyguinula Creek (Canberra 1:100,000 sheet), a tributary of the Molonglo. No work was carried out on these sediments during the present investigations but the descriptions of previous workers suggest they could alternatively be of Tertiary age. II~mmlll~~~I~ D004941981 CAINOZOIC Cainozoic Sediments TERTIARY (not shown on map) Tertiary sediments are fairly rare. However, some are preserved beneath the Whinstone Basalt near Jerang1e. The sediments are consolidated to poorly consolidated. One or two very minor isolated outcrops were also found scattered across the area of the Miche1ago Igneous Complex but they are too small to be indicated on the map. Small areas of ferricrete and greybi11y, overlain by Tertiary basalts, lie just to the southwest of the Miche1ago 1:100,000 sheet area. QUATERNARY (Qa) Sediments of Quaternary age, consisting of sand, gravel, and silt, are found along the Murrumbidgee, Mo1ong10, and Queanbeyan Rivers as well as in several creeks. These sediments are best developed along the Murrumbidgee River. Large quantities of gravel, sand, and silt appear along the Mo1ong10 River flood plain, and small areas of sediments occur on the Queanbeyan River at "Norongo" and along several major creeks. On the downthrown eastern side of the Narongo Fault line many of the small creeks have well-developed a11uviated valleys. West of the fault, bedrock is exposed in creek beds, and thicknesses of alluvium exist up to 9 m deep. The alluvium is usually well stratified and unconsolidated. UNDIFFERENTIATED CAINOZOIC SEDIMENTS (Cza) Browne (1944), Adamson (1955), and Pi11ans (1974) all made reference to sediments developed in the vicinity of Bredbo. Banks and terraces of high-level gravels along the Murrumbidgee River (described by Browne 1944) are particularly abundant near Bredbo and to the south for several kilometres. The terraces are at varying heights above the river but appear to be most common at the 73-m, 45-m, and 25-m levels. Browne thought that all the gravels contained pebbles of basalt and greybi11y, thus implying a younger than Tertiary age. Pi11ans (1974) in a detailed study of the surficial geology of the area south of Bredbo, noted the widely variable rock types present within the Cainozoic gravels. They range from Early Palaeozoic metasediments to Tertiary basalts, clearly reflecting the non-local origin of the gravels. As Pi11ans failed to discover basalt pebbles in some of the older gravels, he postulated that the gravels were deposited between Eocene and Late Quaternary times, II~mmllll~~~~ 0004941982 124 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET the bulk being formed after the close of Early Miocene. Adamson (1955) described several areas of Tertiary sediments cropping out to the southwest of the Michelago sheet area, on the Berridale and Cooma 1:100,000 sheets. He noted, firstly, that many of the gravels are composed of angular and subangular pebbles, and when these occur adjacent to Ordovician quartzites and slates, difficulty was experienced in fixing a boundary between the two types; secondly, that ferruginous rocks are common to both units; and thirdly, that there are difficulties in distinguishing between greybilly and quartz reefs. He briefly described "Tertiary" deposits in Parish Cosgrove, County Beresford which he associated in the same basin of deposition as the larger Tertiary deposits along Caddigat Creek. He postulated an Oligocene age, because of the frequent association of the sediments with basalts. Throughout the Michelago area, sediments have been deposited along most of the creek beds. In some places erosional gullies reveal layered sections over 3 m in depth, with a minor degree of cementation. Talus slopes are also a recent development along the ridges south of Colinton Trig. Station (GR 980283), where large beds of jointed Early Silurian quartzites have weathered to form extensive accumulations of quartzite talus. No indications of bedding exist here. West of the Murrumbidgee River, Cainozoic sediments are developed at the Top Flats (GR 858246), the Long Flat (GR 845237), Shanahans Falls Creek (GR 845326), and Reedy Creek Flat at GR862383. The first two are partial indications of a Holocene to Pleistocene lake, the Naas Lake, which is thought to have developed south and west of Mount Clear. Its existence was postulated by Legge (1937). Cainozoic Basic Rocks TERTIARY WBINSTONE BASALT (Tb) Richardson 1975 The only basic flow existing in the area occurs near Jerangle. Baker (1915) recorded its presence and noted that it was locally referred to as theWhinstone Basalt. Joplin et al. (1953) were the first to show its position on a map. It extends to the southeast of Jerangle for approximatel¥ 7.5 km, from GR 146274 to GR 182211. The body covers some 7 km and forms a narrow ridge elevated some 30 to 60 m above the average granite surface. It has a maximum thickness of about 120 m. Richards (1967) noted at least six smaller flows, each forming a distinct terrace at successively higher levels, and, from observations made on the base level at various points, suggested that the basalt flowed towards the northeast. It is noteworthy that the body follows CAINOZOIC BASIC ROCKS a similar trend to many of the major faults and dykes in the area. Good outcrops can be seen along the ridge at Whinstone Hill. In hand specimen the rock shows olivine phenocrysts set in a dark fine-grained groundmass of slightly variable grainsize. Thin sections reveal subhedral 1 rom crystals of olivine (Foeo) and rare vesicles set in a felted 0.07-rom matrix of plagioclase, olivine, augite, and magnetite. Olivine has brownish octahedral 0.008 rom inclusions of spinel(?). Two small isolated basalt caps are related to the major basalt flow. They appear as rounded hills at GR 174237 and GR 174245. No direct contact between the basalt and the underlying Anembo Granodiorite is visible because the basalt occurs only as float. Thin-section studies reveal subhedral 0.5 rom crystals of olivine (Foeo), brownish titanaugite, plagioclase (Anso), and minor magnetite, as well as rare vesicles. Olivine is partially altered to iddingsite and has 0.008-rom octahedra of spinel as inclusions (picotite?) . The Jerangle flow is believed to be of Tertiary age because of lithological similarity to basalts of known Tertiary age. UNDIFFERENTIATED BASIC PLUGS (n) Olivine Teschenite Plug To the west of the Bredbo-Jerangle road, at GR 123268, a small circular outcrop of basic rock with columnar jointing is present. This rock is most probably a pipe or plug which has intruded a zone of weakness, as it crops out on the line of the Narongo Fault along the contact of the Sapling Flat Igneous Complex and the Kohinoor Volcanics. The rock takes the form of a small conical hill. 125 Richards (1967) first noted the outcrop and considered it to be practically identical with the previously described basalt flow south of Jerangle, except that it is coarse grained. Plagioclase laths within the groundmass average less than 1 rom in length. Because of the abundance of interstitial analcite and its doleritic texture, Richards named it a microteschenite (appendix 2-53). Small Basic Plug to the north of the Califat Gossan A very small outcrop only about a metre in diameter appears on the line of the Narongo Fault, between the Sapling Flat Igneous Complex and the Kohinoor Volcanics, at GR 127298. In composition it would appear to be an altered hornblende gabbro (Barron 1974b). 126 BASIC DYKES GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Dykes crop out extensively over the area of the Michelago 1:100,000 sheet but are frequently concentrated in specific zones. Compositionally they show some variation, and they intrude both granites and Ordovician metasediments. Dolerite dykes are prevalent to the east and north of Jerangle. They intrude the Jerangle Igneous Complex, forming prominent, narrow ridges with a characteristic northwesterly trend and frequent parallelism with the major faults. In width they range from 5 to 9 m and in outcrop appear dark in colour and fine to medium in grainsize. A thin section of a dyke at GR 170253 reveals it to be a mildly altered augite dolerite containing subhedral 0.5 rom clusters of augite crystals, hornblende, skeletal magnetite plates, and plagio- clase fitted together with minor chlorite after hornblende - magnetite, and sericite after plagioclase. Minor pyrite and chalcopyrite have been noted. Rose (1962) and Richards (1967) both mapped these dykes. Basic dykes have been noted in most of the other granite masses as well. Sharp (1949) and Browne (1944) described several minor olivine(?) basalt and quartz dolerite dykes intruding the Murrumbidgee Batholith and the Silurian Bransby Beds and Colinton Volcanics. An excellent example is a kaolinized basic dyke exposed in the railway cutting north of Myall Trig. Station, at GR 948355. Slepecki (1973) noted the presence of several dolerite dykes intruding the Ordovician sediments along the regional trend. The dykes consist of plagioclase, green/brown amphibole, and minor biotite, quartz, and calcite. Some dykes tend to be porphyritic. All show minor alteration but are not affected by the regional metamorphism, so probably post-date the latter. These dykes are located to the north of Ryans Creek north of "Good Good" homestead. In thin section they are found to be hornblende dolerites, containing subhedral 0.5 rom crystals of hornblende, plagioclase (An4s), and minor magnetite. The ends of the hornblende crystals are usually ragged with needles of actinolite(?). The rock has a foliation defined by the alignment of hornblende/plagioclase. The fine needles of actinolite(?) are subparallel to this foliation, suggesting that it is of metamorphic origin. Another concentration of basic dykes has been located to the south of the Tinderry road near Calabash Creek. Some of these dykes are over 9 m in width and appear to have a general northwest trend. Further north, basic dykes become more frequent in outcrop in the Ordovician sediments, generally intruding in a meridional direction, the greatest direction of weakness. One such dyke is of hornblende diorite composition, is foliated, and displays post-tectonic alteration. 127CAINOZOIC BASIC ROCKS Doleritic and dioritic dykes have been described in the vicinity of Captains Flat by Glasson (1957) and Oldershaw (1965). The doleritic dykes which trend northerly, parallel to the regional foliation, cut the Kohinoor Volcanics and, in turn, are frequently out by the northwest-striking faults. Pyrite is not uncommon. A series of north- ~outh-trending concordant diorite lenses is present on the eastern limb of the Captains Flat Synclinorium in the vicinity of Ballallaba Creek (L. Davis pers. comm.). The largest of these is of the order of 900 m long and is 100 m at its widest part. Macroscopically, the diorites are medium-grained, greenish-coloured massive rocks, pegmatitic in places with amphiboles up to 5 mm in length. In thin section they have as much as 60 per cent partially subophitic actinolite as the primary mafic constituent, with andesine plagioclase, epidote, chlorite, and acicular actinolite as alteration products. Ilmenite altering to sphene is a common accessory and comprises up to 10 per cent of the rock. Microdiorites forming occasional outcrops of a medium-grained vesicular dark to grey-green rock are found between Tigercat Creek and the Captains Flat golf course. Randomly oriented laths of andesine feldspar are the dominant primary constituent and these crystals exhibit a wide size range (0.05 to nearly 1 mm). Epidote and actinolite and, to a lesser extent, chlorite and sphene are alteration products after the original mafic constituent, which formed 25 to 30 per cent of the rock. The vesicular nature implies that the intrusion was shallow. Minor occurrences of amphibolites have been noted by Slepecki (1973), to the north of Ryans Creek (GR 101241), and by Oldershaw (1965) within the Boro Granite at GR 253643 and on the banks of Ballallaba Creek (GR 233658) as a lenticular concordant intrusion 90 m wide. PALAEOENVIRONMENTS Ordovician The Adaminaby Beds of the Cotter Anticlinorium are quartz-rich flysch sediments with relatively scarce black shale units, thought by Owen and Wyborn (1974) to be of proximal aspect. The Adaminaby Beds have a high proportion of sandstone units and shallowing water conditions are postulated. Owen and Wyborn considered that the flysch prograded from the west towards the east. Within the Cullarin and Rocky Pic Anticlinoria, the quartz- rich flysch of the Foxlow Beds is of distal aspect. This concept is supported by the higher proportion of shales and siltstones and by the nature of the sedimentary structures and the presence of black shale/chert units. Two conclusions may be reached from the location and mode of outcrop of the black shales of the Foxlow Beds. Firstly, it is apparent that the black shale developed near the top of the Ordovician sequence, although in most cases the so-called top of the Ordovician sequence is a faulted or unconformable boundary with Silurian volcanics/ sediments. Secondly, the slates/cherts represent a quiet period of deep-water marine sedimentation. How conditions arose ~hich would lead to this type of sedimentation is open to debate. Crook et al. (1973) suggested that the "cherts" may represent accumulations in depressions between adajcent submarine fans in areas inaccessible to all but the finest fractions of terrigenous material. Joplin (1945) analysed the black slates and considered them to be of volcanic origin. i.e., redistributed rhyolite tuff. "The black carbonaceous material of the shales has been derived from the decay of masses of seaweed to which the graptolites were either attached or associated" (Joplin 1945, p. 168). Sherrard (1962) noted that it is not necessary to invoke a series of ash showers as the source of the high silica percentage in the slates, for silica may form under normal oceanographic conditions as a primary precipitate of silica gel or by some biochemical means. In some cases the black shales become highly siliceous, forming dense very dark rocks frequently heavily veined with quartz. Cherts with a few recrystallized sponge(?) spicules have been found east of Michelago at GR 980451 suggesting the possible formation of the rock in very still deep water .. Graptolites are the only fauna present in the black shales and they are more or less restricted to these units. They are generally preserved as "chitinous or pyritic films in a highly compressed condition" (Sherrard 1954, p. 74), and because of the extensive cleavage and fracturing in the Late Ordovician rocks most specimens collected in the Michelago area are fragmented and poorly preserved. The dominant siltstone - greywacke content of the Late Ordovician units indicates a period of great sediment accumulation, with the main source of material lying to the west. As coarser 11111\11111111111111111111111\111\111 \\11111111 \11111\111111 0004941983 130 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET grained rocks tend to be more prolific along the western side of the area, with siltstones becoming increasingly common towards the east, the source area was most likely in the west. Early Silurian The Ryrie Formation is essentially a proximal flysch in the terminology of Walker and Sutton (1967), formed under the shallowing water conditions of the Early Silurian. Again the source material was rich in quartz, giving rise to the thick units of quartz greywacke found on Colinton Hill. Like the Late Llandovery State Circle Shale, the unit is virtually devoid of fossils other than a few graptolites and these are relatively scarce in number, a reflection of the unsuitability of the environment for preservation. The basal unit of the Ryrie Formation, the Gungoandra Siltstone Member, probably formed along the periphery of submarine turbidite fans, but the remainder of the formation, which is similar in nature to the Black Mountain Sandstone, possibly represents the axial parts of turbidite fans. For the Mundoonen and Black Mountain Sandstones, Crook et al. (1973) postulated that the thick sand sequences accumulated because of their proximity to sources of turbidity currents. The relatively few graptolites present are restricted to the siltstone bands. They are generally fragmentary in preservation and are ironstained (appendix 1). Pyrite cubes in the shales are perhaps indicative of anaerobic conditions found sporadically through the soft muds in which the graptolites were deposited. Close to the Captains Flat Synclinorium it is quite possible that areas of sediments presently thought to be of Ordovician age are in fact Late Llandovery distal flysch. However, as yet no fossil evidence is available to support this theory. This problem is discussed by Crook et al. (1973) in their study of the southeastern Lachlan Geosyhcline. Late Silurian By the time the Late Silurian began, shallow-water conditions prevailed along the western edge of the area, with the shallow-water sediments of the Cappanana Formation being deposited. Shale, sandstone and limestone formed in a belt stretching from south of Bredbo to north of Burra. The nature of the limestone outcrop indicates that small bioherms were formed offshore with moderate amounts of silt and sand being deposited around the limestone. With a probable western source of sediments, it is quite likely that the sand found near the base of the formation accumulated in areas of moderate currents, while the finer mud was deposited in relatively protected waters on the leeward sides of the reefs. The prolific accumulation of fauna, the nature of the species preserved, and their PALAEOENVIRONMENTS typical presence in siltstones strongly suggests a low-energy environment, while the presence of rounded limestone blocks up to 300 mm in length encased in siltstone beds, and several minor outcrops of limestone breccia, indicate a moderate energy environment with some wave action. Therefore a low to moderate energy environment is postulated for this unit. It may be noted that the formation of limestone corresponds well with a postulated palaeolatitude of approximately 25°S during the Late Silurian (Embleton 1973). Volcanism made its presence felt with the deposition of minor thin tuff beds within the sediments. 131 The continuing presence of small sedimentary lenses, and the occurrence of pumice within many of the beds, suggests that the Colinton Volcanics were deposited in subaqueous conditions. Volcanism continued for some time, a marine character being most commonly indicated. For a short while, near the end of the Ludlovian, marine sediments of the Bransby Beds were able to develop with'the formation of much larger reefs; but volcanism once again quickly enveloped the area, and terrestrial conditions became increasingly obvious. For example, towards the base of the Bransby Beds at GR 925345, the nature of the tuff suggests that the volcanic source was above water, even if the flow may have eventually entered the sea water. To the north, in the vicinity of Williamsdale and Burra, terrestrial volcanism became dominant with the formation of the ash flow tuffs of the Williamsdale Volcanics. No evidence of sedimentary lenses has been found in this area. Therefore, it is quite possible that both the source vents and the area of deposition were located above the water level. East of Tharwa, lacustrine conditions developed, as portrayed by the growth and preservation of inarticulate brachiopods in soft black muds, but this was a fairly restricted development. At most times volcanism was the main source of material deposited throughout the area. Synchronous with the shallow-water deposition in the Bredbo- Burra trough, but further to the east, there was a separate trough around Captains Flat. Here as a result of the increased distance from the continental mass slightly deeper-water conditions prevailed. Both the basal Rutledge Quartzite Member and the Copper Creek Shale have relatively few sedimentary structures, but both contain disseminated pyrite cubes and irregular masses of pyrite. In addition, pyritic lenses are found in the Copper Creek Shale but these are probably of sedimentary origin. Small limestone lenses are also developed within the formation, indicative of sporadic shallower water conditions. The change in environment from marine sediments to volcanics was not rapid as shown by a gradational boundary between the Copper Creek Shale and the Kohinoor Volcanics. Volcanism prevailed through the greater part of the Ludlovian with all volcanic rocks, deposited under, and most likely ejected in, submarine conditions. Volcanism remained dominant to the south of Captains Flat, while deeper water conditions developed again in the north, giving rise to the Carwoola Formation of probable turbidite origin. 132 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The presence of reworked lithic tuffs suggests that shallowing marine conditions prevailed during deposition of the Captains Flat Formation; however terrestrial conditions were also in evidence, as indicated by the presence of basalt lava flows without pillow structures. STRUCTURES AND METAMORPHISM The Michelago area lies within the Lachlan Fold Belt which occupies the central and southeast portions of New South Wales (figure 6). Three structural subdivisions are present within the area, the Canberra Synclinorium of the Cowra - Yass Synclinorial Zone, the Captains Flat Synclinorium of the Captains Flat - Goulburn Synclinorial Zone, and the Molong - South Coast Anticlinorial Zone. The latter includes the Cotter, Cullarin, and Rocky Pic Anticlinoria (figure 7). o 1 234 5 I.'__.I' '............L'__.I'__...I' em f4J' MURRAY BASIN (CRATONIC COVER) Michelogo 1: 100,000 sheet ....-..-- Thrull 33' Tr.nl~'lIlv.bocItIdM," ~ 01 'PINo.,m." m.rg'" of • bum Oth" bound'fI., O,twHn •• I!rur:t"""lIfIIU,.~Iu., 10m. f.ulu REFERENCE _M.!O,r'lIl1.fIt1 -,.v.,.. f~1t K,lomll'" \ '00 SCALE 100 200 ,.' - 33' ,~,' Figure 6. Structural map of New South Wales of the Michelago 1:100,000 sheet showing the position 1111111111111111111111111111111\ 1I11I 1\11111111 111\\ 1I111111 D004941984 1,+ GEOLOGY OF THE MICHELAGO 1:100,000 SHEET 5 SCALE o 5 Kilometres 10 Figure 7. 11111111111111111111111111111111111111111111111 1111111111111 D004941990 Schematic structural o, 1, 2 3I , em 4, 5, r>.<>~~~ I;;HHI 1>:<1 ~ ~........ a -+- -+- STRUCTURES AND METAMORPHISM STRUCTURAL SKETCH MAP REFERENCE Tertiary basalt Early Devonian - granite intrusions, generally massive Late Silurian - Early Devonian - intrusive porphyries Late Silurian - early Early Devonian - open style folding, minor kinking, and strong cleavage Middle Silurian - Late Silurian - granite intrusions, generally foliated Early Silurian - broad, open style folding Late Ordovician - slumping, tight isoclinal folds, slaty cleavage Intrusive boundary Unconformity Fault Major lineament visible on Landsat photograph Anticline Syncline MAJOR FAULTS AND LINEAMENTS 135 Murrumbidgee Fau It 7 Molonglo Fault 2 Burra Fault 8 Sherlock Fault 3 Narongo Fau It 9 Anembo Fault 4 Ballallaba Fault 10 Bold Slate Range Fault 5 Collingwood Fault 11 T inderry Li neament 6 Queanbeyan Fau It map of the Miche1ago 1:100,000 sheet 10514 1111"""" 11"/11"111111""11111111111111111111111111111 0004942000 136 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The effects of four main orogenies, viz. the Benambran, Quidongan, Bowning, and Tabberabberan Orogenies, can be recognized in the Michelago area. Molong - South Coast Anticlinorial Zone The Molong - South Coast Anticlinorial Zone dominates the southern portion of the State and extends across the greater portion of the Michelago area. On the Michelago sheet the western side, termed the Cotter Anticlinorium, is a fault-bounded block while the central and eastern portions, termed the Cullarin Anticlinorium and the Rocky Pic Anticlinorium respectively, are only partially fault bounded (figure 7). The anticlinorial zone includes both Ordovician and Early Silurian flysch sediments and Siluro-Devonian granites. COTTER ANTICLINORIUM Only the southeastern portion of the Cotter Anticlinorium is represented in the Michelago area. The western section has been described by Owen et al. (l974b, in press.). The block is fault bounded in its entirety and composed of granitic bodies and deformed Ordovician flysch sediments; these features are represented in the Michelago area by the Murrumbidgee Fault, the Murrumbidgee Batholith, and the Adaminaby Beds respectively. The Murrwnbidgee Fault. which marks the eastern margin of the anticlinorium, lies parallel and adjacent to the Murrumbidgee River, appearing north of Colinton as a single zone but splitting into three main zones of movement to the south. The presence of the fault is indicated by the development of a heavily dissected scarp along the batholith's eastern boundary. The fault is thought to be a westerly dipping high-angle reverse fault (Noakes 1957, Sharp 1949) than the steep easterly dipping fault with a sinistr?l transcurrent component postulated by Joyce (1973b). In addition, it is quite likely that more than one period of movement has occurred along the fault, a feature common to many of the major faults in the region. Joyce suggested that a transcurrent component was active during and after the batholith's consolidation. The Murrumbidgee Batholith, which dominates the anticlinorium, is regionally concordant with the enclosing Ordovician metasediments. Low-grade, widespread regional metamorphism of the Ordovician sediments took place before the batholith was emplaced and was a result of the last stages of activity of the Benambran Orogeny. With the exception of minor leucocratic intrusions, most of the granitic phases possess a primary foliation with strong alignment of micas and xenoliths. Many phases are also conspicuously sheared in proximity to major faults. For example, the Tharwa Adamellite, outcropping on the west bank of the Murrumbidgee River at Tharwa, displays a superimposed foliation. This foliation is parallel to the Murrumbidgee Fault and its intensity decreases westward away from the fault. Jointing is also well developed in the batholith. STRUCTURES AND METMIORPHISM 137 A most notable feature, clearly delineated on aerial photographs, is the marked northeasterly and northwesterly joint-controlled lineation pattern throughout. Characteristically, a northwesterly trend develops on the western side, i.e., mainly in the Shannons Flat Adamellite, while northeast-trending lineaments occur on the eastern side, within the Clear Range Granodiorite. The lineaments intersect near the northern end of the batholith and a close examination of their relationship suggests that the northeast lineaments are superimposed on the northwest ones. Generally little to no displacment is detected upon the lineaments. The Ordovician Adaminaby Beds have a similar structural style to the Foxlow Beds, Le., isoclinal folds with north - south axes and axial plane cleavage. CULLARIN ANTICLINORIUM The Cullarin Anticlinorium, the central structural block of the area, extends from west of Lake George, south to the New South Wales/Victorian border. The anticlinorium consists of deformed Ordovician and Early Silurian flysch, i.e., the Foxlow Beds and Ryrie Formation respectively, plus numerous minor granitic intrusions, of which the major ones are the Michelago and Sapling Flat Igneous Complexes. Faults are common both along the boundaries and within the anticlinorium. Along the eastern boundary the Narongo Fault separates the anticlinorium from the Late Silurian sediments and volcanics of the Captains Flat Synclinorium and the Ordovician flysch and granites of the Rocky Pic Anticlinorium. The Narongo Fault finds topographic expression in creek patterns and the formation of scarps, the latter being prevalent along the eastern side of the Sapling Flat Igneous Complex. The block east of the fault is downthrown. Around Captains Flat it consists of a zone 15 to 60 m wide of parallel high-angle reverse faults dipping west at 70° to 80° (Oldershaw 1965). It is apparent that more than one period of movement has affected the fault line with rejuvenation of the fault scarp. North of the sheet area the Lake George and Whiskers Faults control the eastern boundary of the anticlinorium. The Queanbeyan Fault is interpreted as extending along the western boundary of the western portion of the Captains Flat-Goulburn Synclinorial Zone. The sense of movement along this fault is not known. The western margin of the Cullarin Anticlinorium is bound by the Burra Fault, formerly considered to be a southward extension of the Queanbeyan Fault. It is developed along the unconformity between the Fowlox Beds and the Colinton and Williamsdale Volcanics, and can be traced by numerous gossans and sulphide-enriched zones, in addition to a strong alignment of topographic features. South of 138 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Michelago, the Burra Fault terminates and, apart from the northwest- ward trending Collingwood Fault, the boundary between the Cullarin Anticlinorium and the Canberra Synclinorium is marked by the eastern edge of the Late Silurian sequence in the Canberra Synclinorium. No lateral movement appears to have taken place along this fault. The Collingwood Fault trends at approximately 335°T. Evidence for the fault is provided by the displacement of both granites and sediments and the prolific development of massive quartz reefs, frequently tens of metres wide (photo 8). The fault displays left- lateral movement and a vertical displacement component of some 4000 m (southern block down) suggested by the seemingly greater displacement of the Ryrie Formation by some 17 km compared with the dislocation of the northern and southern bodies of the Michelago Igneous Complex by some 13 km. The northern and southern extensions of the fault are poorly defined, the northern end passing into the Late Silurian acid volcanics and intrusive porphyry and dying out against the Murrumbidgee Fault near one of the many limestone lenses within the Bransby Beds. A few quartz veins would appear to be the best indication of its presence, although the western porphyry boundary could be partially fault controlled. It is quite possible that the major component of the stress expressed by this fault is taken up by the southward-trending Burra Fault. Consequently, the displacement effect of the Collingwood Fault is minimal northwest of the Monaro Highway, resulting in the Bransby Beds maintaining a fairly consistent thickness along their strike length. The development of large quartz reefs only in the vicinity of the Michelago Igneous Complex would be mainly a result of the greater availability of silica solutions within the granitic mass. Southwards, the Collingwood Fault passes into the Ordovician sediments where it becomes diff{cult to trace because of the absence of stratigraphic markers. The continuance of the Collingwood Fault is suggested by the scale of its displacement near the Michelago Igneous Complex, and the minor alignments in the stream pattern in the Foxlow Beds, to the southeast of the Bredbo - Jerangle road. Complex and minor northeast faults are found in the Foxlow Beds when suitable markers are present. Slumped black cherts are offset by a dextral movement along several small northeasterly trending faults near the Bredbo-Jerangle road at GR 000210 (figure 8). Within the Cullarin Anticlinorium, meridional to submeridional structural trends are dominant. They are reflected in the extremely elongated nature of the granite outcrop, and by the characteristic Ordovician topography with numerous north- south flowing tributary streams. Several styles of deformation are recognized within the Ordovician flysch but not all of these may be attributed to the Benambran Orogeny. 0 1 2 3 4 5 STRUCTURES AND METAMORPHI~M 139, , , , , , em W Quartzite Dominantly Chert Interbedded siltstone Esiltstone and chert Westerly dipping beds Diagram not to 8cale B Overturned Larger folds 10515 Figure 8. Structures developed in the Ordovician Fox1ow Beds in a road cutting on the Bredbo - Jerang1e road at GR 000210 Structures developed include isoclinal folds varying in scale from large and recumbent to small and very tight, axial plane slaty cleavage, flexural slip folds, chevron folds, kinking, and crenulation cleavage (photos 9 and 11). In some areas the second-generation folds are found to be dominantly downward facing, for instance Nisbet (1970) recorded downward-facing folds near Captains Flat. He supported the idea of large recumbent isoclinal folds occurring throughout the region, as suggested by the work of Stauffer and Rickard (1966) to the east of Queanbeyan. However, it is more likely that these structures are huge slumps formed as a result of Benambran Orogenic movement, rather than Bowning movement as postulated by Stauffer and Rickard. The axial plane slaty cleavage formed is frequently vertical and usually coincident with bedding. A crenulation cleavage (refer Rickard 1961 for definition), initiated by flexure, is developed in some areas, for example, at GR 098212 where specimens were found with a crenulation cleavage having a l-rom plane separation. Work carried out by Slepecki (1973) southwest of Jerangle suggests that a later 140 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Photo 11. Disharmonic fold cleavage caused the crenulations to develop at high angles to the bedding at the nose of second-generation folds. It is also possible that crenulation cleavage developed in proximity to faults, as is suggested by the specimens found at GR 098212. Chevron folds are found more particularly near the Sapling Flat Igneous Complex, e.g., at GR 132323. Jointing was a late-stage event and was probably due to the final release of residual stresses. It is particularly well dev~loped in Ordovician sediments at the southern extremity of the Sapling Flat Complex. A fracture cleavage is typically developed within the Early Silurian Ryrie Formation, but it is not as distinctive as the slaty cleavage developed in the Ordovician Foxlow Beds. The broad, open mn 1\1\ 111\11111111\ \I \1\1 0004942010 STRUCTURES AND METAMORPHISM 141 Plunge SW 26° o, 1, 2I .-.- . em 3, 4, 5, E 10518 developed in Ordovician black chert and sandstone at GR 975455 fold structures ,in this formation are not readily visible. By comparison with the Murrumbidgee Batholith, the igneous bodies of the Cullarin Anticlinorium are generally massive. An imposed foliation has developed in proximity to major faults. ROCKY PIC ANTICLINORIUM Along the eastern side of the Michelago 1:100,000 sheet area the Rocky Pic Anticlinorium is represented by further outcrop of the Foxlow Beds and western granites of the Bega Batholith. To the west, the Narongo Fault separates the Rocky Pic and Cullarin Anticlinoria. 11111111111111///111//1/1/11111/11111 1111/111/1 1111111111111 D004942020 '42 GEOLOGY OF THE MICHELAGO 1: 100. 000 SHEET In addition to the major ,'orthward-striking boundary faults, several large northwest-trending faults extend across the Jerangle Igneous Complex. They control stream patterns and l'isplace the boundaries of igneous phases. as well as forming the sites along which large quartz reefs occur. Joint patterns and frequent adjacent and parallel dykes are related to the faults. The ANeMbo3 S'ner>l k, and Bold Slate .'?ar:ge f'CZ:.lZts all ~.ave a general 330 0 T trend, are left lateral in displacement, and have been re~ponsible for rotation of the igneous mass. The Boro Granite has a partly faulted margin northeast of Captains Flat and a strong imposed foliation is associated with this. Generally, however, both the Boro Granite and Jeranqle Igneous Complex have intrusive boundaries. Jointing is developed and has been described under the relevant units. The structures and metamorphism generally developed within the Foxlow Beds have been summarized under the heading "Cul1arin Anticlinorium" (photo 12). phot.o 12. Refolded fold developed in the Fox1ow Beds near t.he Boro Granite at. GR 266653 (photo by court.esy of L. Barron) \ II\UII[ 11111 III I1111 1111 0004942030 STRUCTURES AND METAMORPHISM Cowra - Yass Synclinorial Zone CANBERRA SYNCLINORIUM In the southern part of New South Wales, the Cowra - Yass Synclinorial Zone bifurcates near Burrinjuck Dam. The eastern branch (the Canberra Synclinorium) trends south in a meridional direction through Canberra, Michelago, Bredbo, and Cooma and, after an area obscured by Tertiary basalts, reappears at Quidong. Within the Michelago area, the Canberra Synclinorium is the western and more extensive of the two synclinoria developed. 143 Faults control most of the boundaries of the synclinorium. Along the western margin, the Murrumbidgee Fault separates the Murrumbidgee Batholith from the Late Silurian sediments and volcanics, while in the northeast, the Burra Fault separates the Silurian formations from the Foxlow Beds. The Canberra Synclinorium is formed by a sequence of inter- fingering volcanics and sediments with a generally steeply westward dip. The sediments are most prevalent at the base and top of the sequence. Recent workers (Baczynski 1970, Pillans 1974) have postUlated that the Canberra Synclinorium is a broad synclinal structure and thereby indicated a correlation between the Cappanana Formation and the Bransby Beds. However, evidence for such a structure is not conclusive, as the Murrumbidgee Fault and associated shear zone drastically change the outcrop pattern and tectonic style of the Bransby Beds. Bedding in all units is strongly masked by the cleavage, structural trends within the volcanics are difficult to interpret, and the type of mineralization does not suggest the presence of a syncline (Gilligan in prep.). At present, therefore, no major synclinal structure is recognized, although in small areas minor structures are apparent -- for example, west of Royalla where the Tuggeranong Tuff Member of the Colinton Volcanics is developed in a possible north-plunging syncline. The Bowning Orogeny in the Early Devonian caused strong deformation throughout the region. Some workers (Stauffer and Rickard 1966, Nisbet 1970) have considered that much of the folding recognized within the Ordovician rocks actually occurred in the Bowning Orogeny. Within the Late Silurian rocks, an open style of folding is developed as well as minor kinking (photo 13) and a slaty cleavage. Strong cleavage is well developed, affecting tuffs, mudstones, and limestones, particularly in the vicinity of the Monaro Highway (frontispiece) and the Murrumbidgee River. Meridional trends again dominate as in the Ordovician, and dips are most frequently steeply to the west, although there are some exceptions, especially in the north around Royalla. Folding is best seen in the sediments, particularly the mudstones and limestones. The tuffs, with minor exceptions, tend to display neither folding nor bedding. Fold hinges are rarely observed. Small-scale folds may be observed in tuffs at GR 929599 and in limestones at GR 925516. Kinking is //111//111/1111//1111111111111111111111111111111111111111111 0004942040 144 GEOLOGY OF THE MICHEl.A,O l: 100,000 SH!o;ET photo 13. Kinking developed in siltstones and tuffs of the Colinton Volcanics at GR 961459 most generally secn within the Bransby Beds in greyish slates cropping out along the Murrumbidgee River, for example, to the west of Angle Crossing at GR 899610. Some of the larger scale folds developed in limestones of the Bransby Beds have been induced by movement along the Murrumbidgee Fault line. Captains Flat -Goulburn Synclinorial Zone CAPTAINS FLAT SYNCLINORIUM The Captains Flat Synclinorium, the western limb of the Captains Flat - Caulburn Synclinorial zone, may be traced south from Lake George to Captains Flat. South of the main area of outcrop in the synclinorium, discontinuous occurrences of Silurian rocks appear 11[[1111111 III lUI II ~II D004942050 STRUCTURES AND METAMORPHISM 145 along the line of the Narongo Fault to approximately east of Cooma. The formations of the Hoskinstown Group have been folded into a synclinal structure north of GR 195490. As a result, the Copper Creek Shale and Rutledge Quartzite Member are generally located around the margins of the synclinorium, while the Captains Flat Formation is prominent in the central portion of the belt. The Captains Flat Synclinorium plunges north at an angle of 25° near the Lake George mine area. A pattern of northwest-trending faults dissects the synclinorium, while older, westerly and easterly dipping, high-angle reverse faults control its boundaries (the Narongo and BalZanaba Faults. The northwest-trending faults, which include the Tiger Cat Creek and Golf COU1'se Faults at Captains Flat and the Molonglo Fault~ may be recognized by the offsetting of both folds and north-trending shears. They are not restricted to the Captains Flat Synclinorium but may be traced into the neighbouring anticlinoria. The most important fault is the Molonglo Fault which cuts off the northern extension of the northerly pitching Captains Flat orebody. It and the other faults have generally resulted in a downward and westward movement of the northern blocks. The western section of the Captains Flat - Goulburn Synclinorial Zone which is present along Primrose Valley is mainly represented by Copper Creek Shale and is probably a much shallower body. It is bound by the Queanbeyan Fault which roughly conforms to a northwest trend. The western belt is also roughly dissected by numerous minor faults. As in the Canberra Synclinorium, folding is best seen in the sediments and less frequently in the volcanics. Thus, deformation is more obvious in the Copper Creek Shale than in the Kohinoor Volcanics. For example, the limestones at "Norongo"(GR 180458) display strong kink banding. Fold amplitudes vary from a few centimetres to almost a kilometre, with amplitudes of 1 m to tens of metres most common. A strong north-trending cleavage is also characteristic of the rocks. Conclusions All of the structural zones are partially or wholly fault- bounded by major north - south trending faults. These faults are the oldest linear features in the area and are probably associated with the Quidongan orogenic event. They are the loci along which much of the Silurian volcanic activity took place and many of the faults display more than one episode of activity. Younger northwest and northeast-trending faults were formed mainly as a result of east - west compressive forces. Prominent northwest linears are represented by the Collingwood Fault, the faults in the Jerangle Igneous Complex, the Queanbeyan Fault, and the Tiger Cat Creek, Golf Course, Molonglo, Jinero, and Kanga Faults near Captains Flat. Generally all have a sinistral transcurrent 1/11///111/111//111111111/111/1111111111111111111111111111II 0004942060 146 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET movement. Northeast-trending faults are not as prominent but are present; for example, black chert bands in the Foxlow Beds near GR 000210 are offset by small but numerous fractures. The generalization may be made that most northeast-trending faults have a dextral transcurrent component. Two sets of lineaments are developed within the Murrumbidgee Batholith and again reflect the general northeast and northwest patterns. A third example of the northeast pattern is displayed by the Tinderry Lineament,which crosses the Tinderry Granite and the Foxlow Beds. This lineament may extend to the coast of New South Wales (E. Scheibner pers. corom.) and could be a result of movements during the Mesozoic Era. Episodes of folding and cleavage formation may have been associated with both the Benambran and Bowning Orogenies, and consequently, differing styles of deformation are characteristic of the synclinoria and anticlinoria. Finally, faulting associated with the uplift of the eastern tablelands (the Kosciusko phase) has given rise to the present topography. GEOLOGICAL HISTORY The theory of plate tectonics is invoked to provide a geological history for the area. Much of the explanation is derived from the various works of Scheibner (1972a, b; 1974 a,b), with some modifications after Gilligan (in prep.). Definitions of tectonic provinces, tectonic stages, and basic tectonic units are given by Scheibner (1972a). As the oldest rocks in the area are of Late Ordovician age, the history of the area begins in this period. Within the State's tectonic framework (refer Scheibner 1974) only the Lachlan Pre-Cratonic Province (Lachlan Mobile Zone) and Tasman Epi-Cratonic Province (Tasman cratonic cover) are recognizable within the Michelago area: the latter province has relatively minor significance in the area I s geological history as basalts and sediments of the Late Cretaceous - Cainozoic Tectonic Stage are extremely limited in outcrop. The Lachlan Pre-Cratonic Province is represented by the Benambran - Quidongan, Bowning, and Tabberabberan Tectonic Stages. According to Scheibner (1973), rocks of pre-cratonic provinces are formed in marginal mobile zones while rocks of epi-cratonic provinces represent platforms or covers of cratons. The rocks of the former accumlate at plate margins and form fold belts through structural deformations, in this case, the Lachlan Fold Belt. In this explanation, it is assumed that orogenic events are related to eastward rotation of the Australian plate on several occasions. I Lachlan Pre-Cratonic Province BENAMBRAN - QUIDONGAN TECTONIC STAGE The probable formation of a new Benioff zone in the early Ordovician controlled the Early Ordovician development of the Molong Volcanic Rise by a process of igneous accretion. At the same time a new flysch wedge (trench complex) accumulated in the Monaro Slope and Basin, represented by the Foxlow Beds in the Michelago and Captains Flat area and the Adaminaby Beds further to the west. The Volcanic activity of the Molong Volcanic Rise (volcanic arc) moved eastward with time. Two factors must be considered as possible indications of minor volcanic activity in the Michelago area at this time, although these factors are open to dispute. Firstly, the Foxlow Beds contain a large number of similar bands of black fossiliferous shale and chert which are most common in the upper portion of the sequence. Joplin (1945) carried out petrological and chemical analyses on Ordovician black shales from several areas of New South Wales and her work revealed the presence of an extremely high percentage of silica which she thought could not be accounted for by the normal processes of silicification. Joplin concluded that the slates consist largely of redistributed rhyolite tuff, the result of large accumulations of volcanic ash which encased the fauna and prevented oxidation of the carbon content. Thus, volcanic activity of 1111111111111111111111111111111111111111111111111111111II111 0004942061 148 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Ordovician age is postulated, although it may have been at some considerable distance. The acidity of the proposed volcanics is also in conflict with the recognized basicity (intermediate calc-alkaline) of volcanism on the Molong Volcanic Rise. The second factor to consider is the presence of several meridionally aligned dykes (?) within the great accumulations of Ordovician flysch, both within the Michelago area and further to the east around Braidwood (E.A. Felton pers. comm.). A perfunctory petrological analysis of some dykes (?) revealed them to be of dacitic composition, generally having a strongly foliated matrix. Although these dykes have suffered fairly strong alteration, their presence and alteration could also be accounted for by Late Silurian intrusion and Bowning age deformation. However, there is no satisfactory evidence at present to prove either age conclusively. The Late Ordovician was marked by the hypothetical splitting of the Molong Volcanic Rise under tension, resulting in the development of the Initial Cowra Trough. Following this tension, a possible relative eastward rotation of the Australian plate could have resulted in the Benambran Orogeny. Some minor uplift was experienced at the close of the Ordovician but the main effects of deformation, metamorphism, and elevation were felt more strongly in the west in the Wagga Wagga area. As a result of the greater elevation of the Wagga Marginal Basin, Crook et al. (1973) visualized large gravity-induced flysch nappes sliding eastward and juxtaposed with nappes formed by eastward slip of the western flank of the Quidong -Canberra flysch body (the Foxlow Beds). As described by Piper et al. (1973) and von Huene (1972), large-scale gravity slides or slump structures commonly develop on the continental slopes adjacent to trenches. In an earlier article, Stauffer and Rickard (1966) had postulated the presence of large, isoclinal recumbent folds with wave lengths of the order of kilometres, and suggested possible formation from an eastward movement. They concluded that the folds were post-Silurian in age. However, the structurp.s within the cherts throughout the Foxlow Beds are suggestive of both large-scale and widespread slumping (figure 8 and photo 14) prior to the deposition of the Late Llandovery sediments. Sherwin (1975a) considered a glacially induced eustatic event at the close of the Ordovician to be responsible for the break in sedimentation at that time and the consequent loss of three faunal zones (Zones 19 to 21) in the fossil record of the area. In Early Llandovery times the proximal flysch sediments of the Tantangara Beds formed to the west, but proof of contemporaneous deposition is missing in the Michelago area. Owen and Wyborn (1974) showed evidence for major isoclinal folding and uplift in the mid- Llandoverian, suggesting that deposition of the Tantangara Beds was terminated by a more intense phase of the Benambran Orogeny. This folding and uplift was also experienced towards the east. GEfiLOGICAL HISTOkY 149 Phot.o 14. Deformation in black cher~9 of t.he Foxlow Beds in outcrop on he Bredbo - Jerang1e road at. J:l 000208 Following the last stage of the Bcnaniliran Orogeny, increased extension of the Cowra Trough took place. The late Llandovery (i.e., late Early Silurian) proximal quartz flysch of the Ryrie Formation was deposited between Michelago and Bredbo on the developing Canberra - Yass Rise as a result of erosion of the uplifted land mass to the west. Crook et a1. (1973) suggested that the limited development of late Lla:ldovery units resulted from their fOrmation in submarine fan complexes of variable width which thinned to the east. The Ryrie Formation is correlated with the State Circle Shale and the Black l-'ountain Sandstone of the Canberra area. Deposition during the late Llandovery was of limited duration: it was terminated in the early Wenlock by the Quidongan orogenic movement, which resulted in further elevation, followed by erosion, of the flysch sediments. By this stage, melting of the sedimentary pile had been initiated and the 1urrurnhidgce Batholith was beginning to form in the western area. /[II/ /I ifill In /I 1m/I 0004942070 150 BOWNING TECTONIC STAGE GEOLOGY OF MICHELAGO 1:100,000 SHEET The Bowning Tectonic Stage lasted from the end of the Quidongan orogenic movement to earliest Devonian times. At its commencement a new Benioff zone was possibly forming further to the east but evidence of this is not conclusive. Continuing extension along the eastern margin of the Australian plate led to the formation of fault-bounded blocks in the partially cratonized flysch wedge. As the Cowra Trough continued to widen, the Hill End Trough, a hypothetical new marginal sea, and the associated Captains Flat Trough, displaced en echelon to the south, were in the process of formation. In the Michelago area the development of the southern portion of the Captains Flat Trough as a narrow marginal sea or volcanic rift, and the continued formation of the Canberra - Yass Rise were typical of the Bowning Tectonic Stage. Shallow-water conditions prevailed around the Captains Flat area and conditions became shallower to the south of Canberra. These conditions would account for the greater abundance of limestones within the Cappanana Formation compared with the Copper Creek Shale. In the Michelago area widespread volcanism occurred in the closing stages of the Benambran - Quidongan Tectonic Stage and was associated with subsidence of some of the fault-bounded blocks. It dominated both the Canberra - Yass Rise and the Captains Flat Trough throughout much of the Late SiluJ:ian. Al though water depths were shallow enough to permit the development of minor reef limestones in the Copper Creek Shale, the acid volcanism of the Kohinoor Volcanics was followed by an increase in water depth as the Captains Flat Trough developed. The presence of minor basic volcanism found in the Captains Flat Formation probably signifies the thinning of the underlying continental crust and is typical of volcanic rift bi-modal volcanism. The Kuroko-type sulphide deposits at Captains Flat (Gilligan in prep.) provide evidence for a setting transitional between marginal sea - volcanic rift for the Captains Flat Trough. The Canberra - Yass Rise also experienced considerable acid volcanism with associated rhyodacitic porphyry intrusions. The vents for much of the volcanism were concentrated in the north around Williamsdale where great masses of tuffs accumulated to form the Williamsdale Volcanics. The paucity of shallow-water sediments and the increased thickness of the volcanic pile to the north suggest the higher elevation of this area relative to the southern end. It is possible that some of the later volcanics erupted under terrestrial conditions, although most deposition was obviously marine. Gilligan (in prep.) postulated the existence of limited volcanic rifts for the Canberra - Yass Rise in this area. A decrease in volcanism towards the close of the Silurian Period permitted the formation of the Bransby Beds -- shallow marine sediments with large limestone bodies (compared with those of the Cappanana Formation) and variable developments of tuff. Volcanism terminated to the south near Michelago but continued into the \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\11\\\\\\\\ D004942080 GEOLOGICAL HISTORY Early Devonian around Tharwa, and here possibly both eruption and deposition may have been terrestrial. Lacustrine conditions, as suggested by the presence of inarticulate brachiopods, occurred for a short period east of Tharwa, but only in a restricted area. Bowning orogenic activity began as the Australian plate possibly rotated oceanward once again (Scheibner 1974a) and uplift with associated broad folding and the development of penetrative cleavage affected the whole region. TABBERABBERAN TECTONIC STAGE With renewed intensity of plate movement, the oceanic crust of the marginal sea was subducted and fused, causing orogenic plutonism in the Early Devonian. Numerous small granite masses invaded the Foxlow Beds, and the Bega Batholith was emplaced on the eastern perimeter of the Michelago area. The Murrumbidgee Batholith, which had been intruded during the Quidongan Tectonic Stage, was now in faulted contact with the Late Silurian sediments and volcanics of the Canberra-Yass Rise. The Murrumbidgee Batholith was ~lso exposed by erosion. 151 The Tabberabberan Orogeny in the Middle Devonian signalled the end of the Lachlan Pre-Cratonic Province with cratonization of the marginal seas and rises. Gilligan (in prep.) considers that many of the numerous gold, base metal, and barite vein deposits in the area between Canberra and Cooma may have been emplaced during or after the Tabberabberan Orogeny, as milch of the mineralization is associated with late joints and faults which in places are demonstrably post-Silurian. KANIMBLAN TECTONIC STAGE This stage marked the final development of the Lachlan Fold Belt and its attachment to the pre-existing Australian craton. However, no sediments related to this late phase of development are present in the Michelago area. Tasman Epi-Cratonic Province PERMIAN TECTONIC STAGE Although gravels exposed in the vicinity of Captains Flat have been assigned a Permian age by several workers (e.g., Oldershaw 1965), the deposition of any sediments during the Permian Tectonic Stage is open to dispute. Oldershaw based the Permian age on correlations made with the Fyshwick gravels near Canberra. These were thought by Opik (1958) to be Permianglacials. However, subsequent workers (Jennings 1972) questioned this Permian age and 152 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET considered the Fyshwick gravels to be more likely Tertiary or early Pleistocene fluvial gravels. LATE CRETACEOUS-CAINOZOIC TECTONIC STAGE During the Cainozoic Era, basaltic volcanism was widespread throughout eastern New South Wales. Recent work by Wellman and McDougall (1974) suggested that at least three periods of volcanism were experienced in the Monaro Province. Extensive amounts of basalt were erupted near Cooma, while further north in the Michelago area present day outcrop near Jerangle represents minor flows from a southwesterly direction. Minor episodes of uplift and erosion within the Tertiary were followed by the Kosciusko phase, in which the whole Monaro area was uplifted and its present physiography of fault scarps and valleys was developed. Erosion of the area was renewed and has continued until present times. ECONOMIC GEOLOGY The various aspects of economic geology receive only a cursory treatment in the following notes. The reader is referred to Gilligan (1974a, 1975, and in prep.) for more detailed information. METALLIC MINERALS Intensive prospecting for gold was undertaken throughout much of the Monaro region in the latter half of the nineteenth century. Gold, followed by silver, lead, and zinc was the incentive for numerous small mining ventures which were mainly concentrated in the zones of Silurian outcrop. Mining activities at Michelago, Colinton, and Bredbo are recorded in the literature as early as 1878, with such mines as the Golden Crown reefs and the Bredbo copper - silver - lead mine being worked sporadically. However, the most important and certainly the largest mining venture was at Captains Flat, where Lake George Mines pty Ltd mined and processed over four million tonnes of ore with an average grade of 10 per cent zinc, 6 per cent lead, 0.67 per cent copper, 56 g/t silver and 1.7 g/t gold between 1937 and 1962. By 1962, however, the orebody was depleted and subsequent activity in the area has revolved around the search for another Captains Flat type orebody by various mining companies. Over the last decade mining companies have also been actively engaged in exploration programmes covering the Bredbo- Royalla belt of Silurian acid volcanics and sediments. Smith (1963) has reviewed the mining activities in and around the Australian Capital Territory, while Gilligan (1974a, b, c, 1975 and in prep.) has conducted a comprehensive study and analysis of mineral deposits within the Canberra 1:250,000 sheet area. Gilligan (in prep.) subdivided the area into several structural units, using the terminology of Scheibner (1974b), and grouped the mineral deposi ts of each structural unit. Thus in the Molong - South Coast Anticlinorial Zone the grouping is made on the basis of composition and host rock affiliation into gold - quartz vein mineralization in the Ordovician metasediments (deposit 14); gold, base metal and sometimes barite mineralization associated with the Boro and Braidwood Granites (all to east of Michelago sheet); and contact metamorphic deposits associated with granites (also to east of sheet). The "Ilverton" gossan (3) is a residual iron deposit. The Cowra- Yass Synclinorial Zone mineral deposits include stratabound sulphides at Michelago (34) and Colinton (27); vein base metal (15, 21, 25, 47(?), 48, 49), gold (20, 26, 30-32, 37) and barite (23, 24, 28) deposits present throughout the Silurian belt; and a replacement base metal deposit in limestone near Bredbo (22), many of the deposits being associated with post-Silurian jointing and faulting (16-19, 33, 38-46). A similar situation exists in the Captains Flat- Goulburn Synclinorial Zone: stratabound sulphides occur at the Lake George mine (4) and possibly also at the Anembogossans (10,11) disseminated sulphides at the Federal mine (6) and Bollard prospect (8) vein base metal deposits at the Dam shaft (5, 9(?)), a gold vein 11111111111111111111111111111111111111111111111111111111111\ D004942081 154 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET deposit at Foxlow gold prospect (1), a residual iron deposit related to faulting (2), a barite deposit (12), and a possible contact deposit (13). CONSTRUCTION MATERIALS Railway Ballast In recent years the potential of the area as a source of railway ballast has corne under review as the Goulburn - Bornbala railway line traverses the region between Royalla and Bredbo. Localities with suitable rock characteristics are, for economic reasons, limited to a thin zone of Silurian rocks adjacent to the railway line. The Williamsdale Volcanics would appear to have the most suitable characteristics, as they are relatively uncleaved; they form massive outcrops adjacent to the railway line between Michelago and Williamsdale. Clay The clay and shale resources of the area are not utilized, primarily as a result of the present lack of local ~onsumer demand and the cost involved in transporting the materials to distant large population centres such as Canberra and Cooma. Chesnut (1974a) briefly mentioned wet plastic clays in the vicinity of "Carwoola" and "Foxlow" homesteads just to the north of the sheet area. Griffin and Woodhouse (1970) investigated the brick clay resources of the Captains Flat area. . Sand Sand mining operations have been carried out on a moderate scale along the Murrumbidgee River between Tharwa and Williamsdale. Limitations were placed on the scale of operation by the nature of the deposits, as they are dependent on annual renewal for continued exploitation; however, the absence of overburden, reasonable degree of access, and proximity to Canberra and Queanbeyan made the mining operations economically viable. Three companies formerly operated at GR 883662, GR 910627 and GR 911598. The sand was utilized for construction purposes in the making of concrete and mortar. In the Captains Flat area, small amounts of sand are potentially obtainable by screening river gravel deposits particularly along the Queanbeyan River near "Norongo" (GR 178456), where sandy gravel deposits are found to underlie the flood plain. Because of the shape of the river course, gravel and sand are readily deposited, thus promoting rapid natural rehabilitation. At Bredbo, large amounts of sand have also accumulated near the junction of the Murrumbidgee and Bredbo Rivers, and in view of the ease of access, these could be a viable future source of supply for Cooma. ECONOMIC GEOLOGY Numerous weathered granites existing in the area also have potential for excavation of quartz-rich sands. GraveL 155 Major gravel quarries are nonexistent within the Michelago sheet area. This fact is primarily a reflection of the low degree of demand,as the large population centres of Cooma, Canberra, and Queanbeyan are a minimum distance of 35 km away and consequently have aggregate and roadbase quarries located more conveniently. Several minor road gravel pits lie along the Monaro Highway between Royalla and Bredbo, at GR 951439, GR 956515, GR938221,andGR950390. They are generally located in rhyolitic to rhyodacitic cleaved tuffs. The Naas Road south of Tharwa, the Bredbo -Jerangle road, the Michelago-Burra road, and the Captains Flat Road all have suitably adjacent road gravel pits. These pits have been, or still are, the source of much of the road gravel for the secondary road network. Generally the pits are in mudstone/ siltstone or sheared porphyritic acid volcanics, wit~ only one or two in granite. Limestone Numerous bodies of limestone crop out, mainly within the Royalla-Bredbo belt of Silurian sediments and volcanics, with minor occurrences also noted in the Captains Flat Synclinorium and its southern outliers along the Narongo Fault. Only the limestones of the Bransby Beds are extensive enough to be of some economic importance but to date only minor quarrying has taken place. Carne and Jones (1919) described one small body west of Gungoandra Creek that was mined and burned for local lime requirements. Marble leases were also held on limestones at GR 933449. Recent years have seen a renewal of interest in the Murrumbidgee River limestones, as the rock is considerably recrystallized and suitable for building purposes. Stone at GR 003527, near "Spring Valley" homestead, has also been quarried for local lime requirments. Minor limestone bodies in the vicinity of Captains Flat (GR 213625) and at "Norongo" (GR 178460) have been quarried in the past for use as flux in the Captains Flat smelter. In considering such economic factors as access and size of outcrop, the major limestone bodies along the Murrumbidgee River are quite suitable for use as building material. But, for the purposes of industrial and agricultural lime, any suitable limestones are either too limited in extent or are somewhat inaccessible so that transport costs (presumably to Canberra and Queanbeyan) would probably be prohibitive. 156 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET ACKNOWLEDGEMENTS The author wishes to acknowledge the assistance provided in discussions with M. Owen and other personnel of the Bureau of Mineral Resources; L. Davis of Electrolytic Zinc Co. of A/asia Ltd.; staff of the Department of Geology and Reoearch School of Earth Sciences, Australian National University; and personnel of the Geological Survey of New South Wales. SELECTED BIBLIOGRAPHY File numbers given in brackets at the end of a reference refer to material held in the Geological Survey of New South Wales information system. ANU (See Australian National University). Adamson, C.L., 1955. Reconnaissance geology of Snowy Mountains area. Progress report No.4. Adaminaby. A. Rep. Dep. Mines N.S.W. for 1951, 78-86. ------------, Wallis, G.R., and Frenda, G.A., 1964. Short Notes on various Building Stone Deposits in New South Wales. Rep. geoZ. Surv. N.S.W•• 19. 20 pp. Alpex Ltd, 1975. Report on literature research, Exploration Licence No. 614 [Bredbo, Colinton, Michelago area]. Rep. AZpex Ltd (unpubl.) (GS 1975/030). (See also Amax Exploration (Australia) Inc., Bates and Shepherd 1971; Besley 1972a, b; Layton and Associates pty' Ltd 1970; Shepherd and Bates 1971; Tenneco Australia Inc. 1972; Young 1974a, b). Amax Exploration (Australia) Inc., 1971a. Quarterly reports Nos 1-5, EL 308, Cooma-Michelago area -- for Alpex Ltd. FiZe geoZ. SUPV. N.S.W•• GS 1971/111 (unpubl.) • -------------------------------, 1971b. Quarterly reports Nos 3-5, EL 239, Cooma-Bredboarea. FiZegeoZ. Surv. N.S.W•• GS1971/284 (unpubl.). -------------------------------, 1972. Quarterly reports Nos. 8-12, EL 239, Cooma - Bredbo area -- with Tenneco Australia Inc. for Alpex Ltd. Fi Ze geo Z. Surv. N.S.W•• GS 1972/409 (unpubl.). (See also Bates and Shepherd 1971, Shepherd and Bates 1971, Tenneco Australia Inc. 1972). Amdel (See Australian Mineral Development Laboratories, The). Anaconda Australia Inc. (See Kennedy 1966). Andrews, E.C., 1905. INTRODUCTION TO THE PHYSICAL GEOGRAPHY OF NEW SOUTH WALES. Brooks, Sydney. ------------, 1910. Geographical unity of eastern Australia in late and post Tertiary time, with applications to biological problems. J. Proc. R. Soc. N.S.W•• 44, 420-480. ------------, 1934. The or~g~n of modern mountain ranges. With special reference to the eastern Australian highlands. J. Proc. R. Soc. N.S.W.• 67(2), 251-350. Australian Mineral Development Laboratories, The (AMDEL), 1977. Analyses of igneous rocks from Michelago 1:100,000 Geological Sheet. Rep. for Bur. Miner. ResGUr. GeoZ. Geophys Aust. (unpubl.) (GS 1977/237). (See also Rowley 1975). II11111111111111111111111111111111111111111111111111111IIII1 D004942082 158 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Australian National University, Department of Geology, 1972. Third-year student field project. Rep. Aust. natn. Univ., Canberra (unpub1.). -------------------------,1973. Third-year student field project. Rep. Aust. natn. Univ., Canberra (unpubl.). -------------------------, 1974. Tnird-year student project. Rep. Aust. natn. Univ., Canberra (unpubl.). Baczynski, N.R.P., 1970. Geology east of Bredbo, N.S.W. B.Sc. Hons Thesis, Aust. natn. Univ., Canberra (unpub1.). Baker, R.T., 1915. Ed. Ser., 19. Building and Ornamental Stones of Australia. 169 pp. N.S.W. tech. Barron, J., 1971. Some mines in the area south southeast of Canberra. Rep. geoZ. Surv. N.S.W., Pet. 1971/34 (unpubl.) (GS 1971/610). ---------, 1972. Petrographic notes on Captains Flat and Wagga areas. Rep. geoZ. Surv. N.S.W., Pet. 1972/20 (unpub1.) (GS 1972/125). Barron, L.M., 1974a. Petrology of samples from the Miche1ago 1:100,000 region. Rep. geoZ. Surv. N.S.W., Pet. 1974/10 (unpub1.) (GS 1974/172). -----------, 1974b. Some granitic rocks from the Michelago 1:100,000. Rep. geoZ. Surv. N.S.W., Pet. 1974/29 (unpubl.) (GS 1974/223). -----------, 1974c. Some volcanics and porphyries from the Miche1ago 1:100,000. Rep. geoZ. Surv. N.S.W., Pet. 1974/32 (unpub1.) (GS 1974/267). -----------, 1974d. Some sediments from the Miche1ago 1:100,000. Rep. geoZ. Surv. N.S. W" Pet. 1974/33 (unpubl.) (GS 1974/233). ----------, 1974e. Some porphyritic rocks for railway ballast quarry sites on the Gou1burn-Bomba1a line. Rep. geoZ. Surv. N.S.W., Pet. 1974/67 (unpubl.) (GS 1974/472). ----------, 1974f. 1:100,000 area. Some granites, porphyries and sediments from the Miche1ago Rep. geoZ. Surv. N. S. W., Pet. 1974/74 (unpubl.) (GS 1974/478) • ----------, 1974g. Some volcanics and granites from the Miche1ago 1:100,000. Rep. geoZ. Surv. N.S.W., Pet. 1974/76 (unpubl.) (GS 1974/488). ----------, 1975a. Some rocks from the Captains Flat 1:50,000. Rep. geoZ. Surv. N.S.W., Pet. 1975/2 (unpubl.) (GS 1975/006). ----------, 1975b. Some rocks from the Captains Flat 1:50,000. Rep. geoZ. Surv. N.S.W., Pet. 1975/3 (unpub1.) (GS 1975/007). ----------, 1975c. Some volcanics, porphyries and sediments from the Miche1ago area; especially the Co1inton Volcanics. Rep. geoZ. Surv. N.S.W., Pet. 1975/12 (unpubl.) (GS 1975/063). SELECTED BIBLIOGRAPHY 159 ---------------, 1975d. Some rocks from the western Urialla Granite. Rep. geol. Surv. N.S.W., Pet. 1975/33 (unpubl.) (GS 1975/145). Bates, C.D.S., and Shepherd, N., 1971. Quarterly report No.6, Mineral Exploration Licence No. 239 [Cooma - Bredbo area]. Rep. Amax Exploration (Aust.) Inc. for Alpex Ltd (unpubl.) (GS 197.1/507). Besley, R.E., 1972a. Summary report and diamond drill hole proposal, Harnett prospect -- M.E.L. 239, Cooma - N.S.W. Rep. Tenneao Australia Ina. for Alpex Ltd (unpubl.) (GS 1972/403). -------------, 1972b. Completion report, diamond drill hole H.D.D. 1, Harnett prospect, M.E.L. 239 -- Cooma - N.S.W. Rep. Tenneao Australia Ina. for Alpex Ltd (unpubl.) (GS 1972/403). Best, J.G., D'Addario, G.W., Walpole, B.P., and Rose, G., 1964. Canberra 1:250,000 Geological Sheet SI 55-16. 2nd edn. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. Branagan, D.F., and Packham, G.H., 1967. FIELD GEOLOGY OF NEW SOUTH WALES. 191 pp. Science Press, Sydney. Branch, C.D., 1966. Volcanic Cauldrons, Ring Complexes, and Associated Granites of the Georgetown Inlier, Queensland. Bull. Bur. Miner. ResoUT'. Geol. Geophys. Aust., 76. 159 pp. Brooks, C.H., and Leggo, M.D., 1972. The local chronology and regional implications of a Rb-Sr investigation of granitic rocks from the Corryong district, southeastern Australia. J. geol. Soa. Aust., 19(1), 1-19. Brown, D.A., Campbell, K.S.W., and Crook, K.A.W., 1968. THE GEOLOGICAL EVOLUTION OF AUSTRALIA AND NEW ZEALAND. 409 pp. Pergamon Press, London. Brown, H.B., 1928. The geology and physiography of the Michelago and Colinton district. B.Sa. Hons Thesis, Univ. Sydney, Sydney (unpubl.). Brown, I.A., 1932. Late Middle Devonian diastrophism in south-eastern Australia. Proa. Linn. Soa. N.S.W., 57(5-6), 323-331. -----------, 1933. The geology of the south coast of New South Wales, with special reference to the origin and relationships of the igneous rocks. Proa. Linn. Soa. N.S.W., 58(5), 334-362. -----------, and Sherrard, K.M., 1952. Graptolite zones in the Silurian of the Yass-Bowning district of New South Wales. J. Proa. R. Soa. N.S.W., 85(4), 127-134, pls vii - viii. Browne, W.R., 1914. The geology of the Cooma district, N.S.W. Part I. J. Proa. R. Soa. N.S.W., 48, 172-222. ------------, 1929. Presidential address. An outline of the history of igneous action in New South Wales till the close of the Palaeozoic Era. Proa. Linn. Soa. N.S.W., 54(1), ix-xxxix. 160 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET -----------, 1931. Notes on bathyliths and some of their implications. J. Froc. R. Soc. N.S.W., 65, 112-144. -----------, 1944. The geology of the Cooma district, N.S.W. Part II. The country between Bunyan and Colinton. J. Froc. R. Soc. N.S.W., 77(4), 156-172. -----------, 1947. A short history of the Tasman Geosyncline of eastern Australia. Sci. Frog. Lond., 35(140), 623-637. -----------, 1950. Metallogenic epochs and ore regions in the Commonwealth of Australia. J. Froc. R. Soc. N.S.W., 83, 96-113. -----------, 1953. Account of mountain-building movements in Australia. Froc. 7th Pan-Pacif. Sci. Congr., 2, 92-102. -----------, 1972. Grey billy and its associates in eastern Australia. Froc. Linn. Soc. N.S.W., 97(2), 98-129. -----------, Dulhunty, J.A., and Maze, W.H., 1944. Notes on the geology, physiography and glaciology of the Koscuisko area and the country north of it. Froc. Linn. Soc. N.S.W., 69(5-6), 238-252. Brunker, R.L., Offenberg, A.C., and West, J.L., 1971. Monaro 1:500,000 Geological Sheet. Geol. Surv. N.S.W., Sydney. Bureau of Meteorology,Commonwealth of Australia, 1966. Rainfall Statistics New South Wales. Director of Meteorology, Melbourne. Bureau of Mineral Resources, Geological Branch., 1974. Annual summary of activities 1974. Rec. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1974/127 (unpubl.). Burton, G.M., 1967. Recharge conditions and the siting of bores in fractured-rock aquifers of the A.C.T. Rec. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1967/93 (unpubl.). Canavan, F., 1953. Cowarra gold mine, in Geology of Australian Ore Deposits. 5th Firrp. Min. Metall. Congr. Aust. N. Z., 1, 941-943. -----------, 1965. The relation between faulting and mineralization at the Cowarra gold mine in New South Wales. Froc. AustraZas. Inst. Min. Metall., 216, 13-16. Carne, J.E., 1908. The Copper-Mining Industry and the Distribution of Copper Ores in New South Wales. 2nd edn. MineraZ Resour. geoZ. Surv. N.S.W., 6.425pp. -----------, and Jones, L.J., 1919. The Limestone Deposits of New South Wales. MineraZ Resour. geoZ. Surv. N.S.W., 25. 411 pp. Chappell, B.W., and White, A.J.R., 1974. Two contrasting granite types. Pacif. GeoZ., 8, 173-174. Chestnut, W.S., 1972. preliminary geological investigation of the nature and composition of mine tailings in the vicinity of Captains Flat. Rep. geoZ. Surv. N.S.W., GS 1972/402 (unpubl.). SELECTED BIBLIOGRAPHY -----------------, 1974a. Rehabilitation of Captains Flat mine dumps. Preliminary geological appraisal of sources of extractive contruction materials. Rep. geoZ. Surv. N.S.W., GS 1974/051 (unpubl.). -----------------, 1974b. Preliminary geological appraisal of Forsters Creek valley (Captains Flat) in terms of proposal to seal with concrete. Rep. geoZ. Surv. N.S.W., GS 1974/338 (unpubl.). Clarke, W.B., 1853. On the geology of the left bank of the upper Murrumbidgee. ParZiamentary BZue Book, Feb. 28th, 1853, pp. 33. -----------, 1860. RESEARCHES IN THE SOUTHERN GOLD-FIELDS OF NEW SOUTH WALES. 305 pp. Reading and Wellbank, Sydney. 161 Cleary, J.R., 1967. The seismicity of the Gunning and surrounding areas, 1958-1961. J. geoZ. Soc. Aust., 14(1) " 23-29. Cominco Exploration pty Ltd (See Young 1974a, b). Compston, W., and pidgeon, R.T., 1962. Rubidium - strontium dating of shales by the total-rock method. J. geophys. Res., 67(9), 3493-3502, Conaghan, H.F., and Foskett, W.E., 1955. Geochemical and geophysical prospecting at Captain's Flat. A. Rep. Dep. Mines, N.S.W. for 1949, 90-101. Conwest (Australia) N.L. (See Larson 1972). Costin, A.B., 1954. A STUDY OF THE ECOSYSTEMS OF THE MONARO REGION OF NEW SOUTH WALES with Special Reference to Soil Erosion. 860 pp. Govt. Printer, Sydney. Cottle, V.M., 1969. Final report, New South Wales Exploration Licence No.1, the Captains Flat - Queanbeyan - Cooma area. Rep. EZectroZytic Zinc Co. of A/asia Ltd (unpubl.) (GS 1969/468). -----------, 1970. Harnett area. Captains Flat exploration project. Final report Michelago- Rep. EZectroZytic Zinc Co. of A/asia Ltd (unpubl.) (GS 1970/059). Cotton, C.A., 1949. A review of tectonic relief in Australia. J. GeoZ., 57(3), 280-296. Craft, F.A., 1933. The surface history of Monaro, N.S.W. ~oc. Linn. Soc. N.S.W., 58(3-4), 229-244. Crespin, I., 1959. Microfossils in Australian and New Guinea stratigraphy. J. ~oc. R. Soc. N.S.W., 92(4), 133-147. Crook, K.A.W., Bein, J., Hughes, R.J., and Scott, P.A., 1973. Ordovician and Silurian history of the southeastern part of the Lachlan Geosyncline. J. geoZ. Soc. Aust., 20(2), 113-143. David, T.W.E., 1950. THE GEOLOGY OF THE COMMONWEALTH OF AUSTRALIA. 1365 pp. W.R. Browne (Ed.). Edward Arnold and Co., London. 162 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Davis, L.W., 1974. Final report on Exploration Licence No. 103. Rep. Eleotrolytio Zino Co. of A/asia Ltd (unpubl.) (GS 1974/489). -----------, 1975. Captains Flat orebody, in Economic Geology of Australia and Papua New Guinea. 1. Metals. Monogr. Australas. Inet. Min. Metall., 5, 694-700. Dolanski, J., 1971. Mineralogical and X-ray examination of field sample No. M-a, three miles north of Michelago N.S.W. Rep. geol. Surv. N.S.W., Minera1og. 1971/2 (unpubl.) (GS 1971/083). -----------, 1972. ~lineragraphic examination of gossan samples from the Anembo area, south of Captain's Flat, N.S.W. Rep. geol. Surv. N.S.W., Minera1og.1972/20 (unpubl.) (GS 1972/175). ------------, 1975. Tourmaline, zeolites and tainiolite from the Michelago area. Rep. geol. Surv. N.S.W., Minera1og. 1975/23 (unpubl.) (GS 1975/135). Duffy, P.J.B., 1969. Land use in the Queanbeyan-Shoalhaven area in Lands of the Queanbeyan - Shoalhaven Area, A.C.T. and N.S.W. Land Res. Ser. C.S.I.R. O. Aust.,24, 134-149. Edwards, A.B., 1943. The composition of the lead - zinc ores at Captains Flat, N.S.W. Proo. Australas. Inst. Min. Metall., 129, 23-40. ------------, and Baker, G., 1953. The composition of the lead - zinc ores at Captains Flat, N.S.W. II. Proo. Australas. Inst. Min. Metall., 170, 103-131. Electrolytic Zinc. Co. of A/asiaLtd, 1966a.Quarterly reports, EL 1, Captains Flat. File geol. Surv. N.S.W., GS 1966/137 (unpubl.). --------------------, 1966b. Drilling aid, EL 1, Colinton area. File geol. Surv. N. S. W., GS 1966/169 (unpubl.) •• ----------------------, 1966c. Drilling aid, EL 1, Captains Flat. File geol. SUPV. N.S.W., GS 1966/178 (unpubl.). ----------------------------, 1967a. Drilling aid, EL's 1 and 106, Michelago area. File geol. Surv. N. S. W., GS 1967/052 (unpubl.). ------------------------, 1967b. Geophysical profiles, Harnett prospect, EL 1, Captains Flat. File geol. Surv. N.S.W., GS 1967/330 (unpubl.). ---------------------, 1969. Drilling aid application, EL 103, Gourlay- Hickey area, Captains Flat. File geol. Surv. N.S.W., GS 1969/203 (unpubl.). ------------------------, 1970. Exploration reports, EL 103, Captains Flat area. File geoZ. Surv. N.S.W., GS 1970/307 (unpubl.). SELECTED BIBLIOGRAPHY ----------------------------------, 1972. Drilling aid [1972-1974], EL 103, Captains Flat. FiZe geoZ. Surv. N.S.W.• GS 1972/309 (unpubl.). (See also Cottle 1969, 1970; Davis 1974; Whitten 1952). Embleton, B.J.J., 1973. The palaeolatitude of Australia through Phanerozoic time. J. geoZ. Soa. Aust .• 19(4), 475-482. 163 ----------------, McElhinny,M.W., Crawford,A.R., and Luck, G.R., 1974. magnetism and the tectonic evolution of the Tasman Orogenic Zone. Soa. Aust .• 21(2), 187-193. Palaeo- J. geoZ. Etheridge, R. Jnr, 1907. A Monograph of the Silurian and Devonian Corals of New South Wales: with illustrations from other parts of Australia. Part II. -- The Genus TrypZasma. Mem. geoZ. SurV. N.S.W.• Pa1aeont. 13, 41-102, pIs X-XXVIII. -----------------, 1917. An Australian Amphipora. Rea. Aust. Mus •• 11(11), 239-241, pIs 44-45. Evernden, J.F., and Richards, J.R., 1962. Potassium - argon ages in eastern Australia. J. geoZ. Soa. Aust .• 9(1), 1-49. Fairbridge, R., 1953. AUSTRALIAN STRATIGRAPHY. 2nd edn. Univ. West. Aust. Press. Faulkner, J.W., 1975. Report of activities on Exploration Licence 760 (Spring Valley - Michelago area, N.S.W.). Rep. OaaidentaZ MineraZs Corporation of AustraZia (unpubl.) (GS 1975/235). Felton, E.A., 1974. Stratigraphic revisions in the Tarago - Woodlawn - Mount Fairy area. Q. Notes geoZ. Surv. N.S.W.• 17, 7-12. and Huleatt, M.B., 1975. Braidwood 1:100,000 Geological Sheet 8827. Geol. Surv. N.S.W., Sydney. 8827 . and -------------, 1977. Geology of the Braidwood 1:100,000 Sheet 97 pp. Geol. Surv. N.S.W., Sydney. Fisher, N.H., 1943. Report on the Bredbo barite deposits. Rea. Bur. Miner. Resour. GeoZ. Geophys. Aust .• 1943/46 (unpubl.). -------, 1947a. Lead. Swrun. Rep. Bur. Miner. ResQur. GeoZ. Geophys. Aust•• 23. 44 pp. ------, 1947b. Zinc. Swrun. Rep. Bur. Miner. Resour. GeoZ. Geophys. Aust.• 33. 30 pp. Forsayth Mineral Exploration N.L., 1974. Exploration reports, EL 654. Bredbo- Colinton area. FiZe geoZ. Surv. N.S.W•• GS 1974/115 (unpubl.). 164 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Galloway, R.W., 1965. Late Quaternary climates in Australia. J. Geol., 73(4),603-618. Garretty, M.D., 1937. Geological notes on the country between the Yass and Shoalhaven Rivers. J. Proc. R. Soc. N.S.W., 70(2), 364-374. Geological Society of Australia , 1973. Australian Code of Stratigraphic Nomenclature. Revised 4th edn. J. geol. Soc. Aust., 20(1), 105-112 •. Geological Survey of New South Wales, 1941. Michelago ironstone deposits. Rep. geol. Surv. N.S.W., GS 1941/023 (unpubl.). Geoterrex Ltd (See Rattew et al. 1973). Gibbons, G.S., 1962. Gravity investigations at Captains Flat, N.S.W. Rep. geol. Surv. N.S.W., 6. 5 pp. Gilligan, L.B., 1972. Geochemistry of the Michelago gossans. Rep. geol. Surv. N.S.W., GS 1972/087 (unpubl.). --------------, 1974a. Canberra 1:250,000 Metallogenic Map SI 55-16. Geol. Surv. N.S.W., Sydney. --------------, 1974b. Cowra - Yass Synclinorial Zone, in THE MINERAL DEPOSITS OF NEW SOUTH WALES, pp. 216-230. N.L. Markham and H. Basden (Eds). Geol. Surv. N.S.W., Sydney. --------------, 1974c. Captains Flat - Goulburn Synclinorial Zone, in THE MINERAL DEPOSITS OF NEW SOUTH WALES, pp. 294-306. N.L. Markham and H. Basden (Eds). Geol. Surv. N.S.W., Sydney. --------------, 1975. 1:250,000 Sheet. Mine Data Sheets to accompany Metallogenic Map, Canberra Geol. Surv. N.S.W., Sydney. --------------, in prep. A Metallogenic Study of the Canberra 1:250,000 Sheet SI55-l6. Geol. Surv. N.S.W., Sydney. Glasson, K.R., 1951. General geology, Captains Flat. Rep. Lake George Mines pty Ltd (unpubl.) (GS 1951/034). -------------, 1952. Geological report, Captains Flat, N.S.W. Rep. Lake George Mines Pty Ltd (unpubl.) (GS 1952/082). -------------, 1957. The regional geology and structures of an area around Captain's Flat (N.S.W.) and their influence on mineralisation and formation of the ore bodies. M.Sc. Thesis, Univ. Sydney, Sydney (unpubl.). and Paine, V. R., 1965. Lead - zinc - copper ore deposits of Lake George Mines, Captains Flat, in Geology of Australian Ore Deposits. Publs 8th Commonw. min. metall. Congr., Aust., N.Z., 1, 423-431. Griffin, O.K., and Woodhouse, J.W., 1970. Brick clay resources of the Captains Flat area. Rep. geol. Surv. N.S.W., GS 1970/012 (unpubl.). SELECTED BIBLIOGRAPHY Griffin, R.J., and Wynn, D.W., 1962. Iron. Mineral Ind. geol. Surv. N.S.W., 21. 48 pp. Gunn, R.H., 1969. Soils of the QUeanbeyan - Shoa1haven area, in Lands of the QUeanbeyan - Shoa1haven Area, A.C.T. and N.S.W. u:r.nd Res. Ser. C.S.I.R.O. Aust., 24, 92-112. Hall, L.R., 1959. Manganese. Mineral Ind. geol. Surv. N.S.W., 25. 31 pp. ----------, Rose, G., and Pogson, D.J., 1967. Bega 1:250,000 Geological Sheet SJ 55-4. Geo1. Surv. N.S.W., Sydney. Hall, T.S., 1902. The graptolites of New South Wales, in the collection of the Geological Survey. Rec. geol. Surv. N.S.W., 7, 49-59, p1s 12-14. Hancock, P.M., 1963. Geology of the Bredbo and Miche1ago 1:50,000 sheet areas, southern N.S.W., with appendices on Ordovician graptolites by S.K. Skwarko and petrology by W.R. Morgan and W. 01dershaw. Rec. Bur. Miner. ResOUP. Geol. Geophys. Aust., 1963/70 (unpub1.). Hanlon, F.N., 1946. The bauxites of New South Wales, their distribution, composition, and probable origin. J. Proc. R. Soc. N.S.W., 78(3),94-112. 165 Harding, R.R., 1966. Catalogue of age determinations carried out by the K-Ar, Rb-Sr, Re-Os, and Pb methods on Australian rocks between June 1962 and December 1965. Rec. Bur. Miner. ResOUP. Geol. Geophys. Aust., 1966/22 (unpub1.). Harland, W.B., Smith, A.G., and Wilcock, B., (Eds), 1964. The Phanerozoic Time- Scale. Q. Jl geol. Soc. Lond., 1205. Harper, L.F., 1916. Report on recent discovery of alluvial tin near Boro. A. Rep. Dep. Mines N.S.W. for 1915, 187-188. ------------, 1928. Upper Ordovician slates, Queanbeyan. A. Rep. Dep. Mines N.S.W. for 1927, 108. ------------, 1929. Captains Flat mineral belt. A. Rep. Dep. Mines N.S.W. for 1928, 107-108. Harris, W.J., and Keb1e, R.A., 1929. A collection of graptolites from the Federal Territory. Proc. R. Soc. Viet., (n.s.) 42(1), 27-29. Hickingbottom, J.L., 1972. The geology of the Baldwin area, Captains Flat, N.S.W. Geology Fellowship Diploma Thesis, R. Melbourne Inst. Tech. (unpub1.). Hobbs, J.J., 1973. Geochemical sampling of the "Anembo Gossans" south of Captains Flat. Rep. geol. Surv. N.S.W., G51973/028 (unpub1.). Hopwood, T.P., 1966. The relationship between tectonic style and metamorphic grade in the Cooma Complex, N.S.W. Ph.D. Thesis, Univ. Sydney, Sydney. (unpubl.). Horner, D., 1973. The geology of an area east of Bredbo, N.S.W. Fourth-year field project. Rep. Aust. natn. Univ., Canberra (unpubl.). 166 Huleatt, M.B., 1971. Flat districts. GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Correlation of Silurian rocks in the Braidwood and Captains Q. Notes geol. Surv. N.S.W., 3, 16-18. Irving, J.L., 1971. Report on a combined airborne geophysical survey, Cooma area, New South Wales. Rep. Seigel Associates Australasia Pty Ltd (unpubl.) (GS 1971/111). Ivanac, J.F., and Marshall, N.J., 1965. Geochemical sampling -- Michelago area, New South Wales. Rec. Bur. Miner. Resour. Geol. Geophys. Aust., 1965/204 (unpub1.) . Jaeger, H., 1967. Preliminary stratigraphical. results from graptolite studies in the Upper Silurian and Lower Devonian of southeastern Australia. J. geol. Soc. AU8t., 14(2), 281-286, pl. 14. Jaquet, J.B., 1901. The Iron Ore Deposits of New South Wales. Mem. geoZ. Surv. N.S.W., Geo1. 2. 186 pp. Jennings, J.N., 1972. The age of Canberra landforms. J. geoZ. Soc. Aust., 19(3), 371-378. Johnson, N.E.A., 1964. The geology of the Krawaree area, N.S.W. M.Sc. Thesis, Aust. natn. Univ., Canberra (unpub1.). Jones, L.J., 1925. Limestone, Dolomite, Lime, and Hydraulic Cement. BulZ. geoZ. Surv. N.S.W., 9. 37 pp. Joplin, G.A., 1942. Petrological studies in the Ordovician of New South Wales. I. The Cooma Complex. Froe. Linn. Soc. N.S.W., 67(3-4), 156-196. ------------, 1943. Petrological studies in the Ordovician of New South Wales. II. The northern extension of the Cooma Complex. Proe. Linn. Soc. N.S.W., 68(5-6), 159-183. ------------, 1945. Petrological studies in the Ordovician of New South Wales. III. The composition and origin of the Upper Ordovician graptolite-bearing slates. Froe. Linn. Soc. N.S.W., 70(3-4), 158-172. ------------, 1962. An apparent magmatic cycle in the Tasman Geosyncline. J. geol. Soc. Aust., 9, 51-69. ------------, 1963. Chemical Analyses of Australian Rocks. Part I: Igneous and Metamorphic. BulZ. Bur. Miner. Resour. GeoZ. Geophys. Aust., 65. 446 pp. ------------, 1965. Chemical Analyses of Australian Rocks. Part II: Sedimentary Rocks. Bull. Bur. Miner. Resour. Geol. Geophys. Aust., 78, 235 pp. -----------, 1968. A PETROGRAPHY OF AUSTRALIAN METAMORPHIC ROCKS. 262 pp. Angus and Robertson Ltd, Sydney. -----------, 1972. A PETROGRAPHY OF AUSTRALIAN IGNEOUS ROCKS. 3rd edn. 253 pp. Angus and Robertson Ltd, Sydney. SELECTED BIBLIOGRAPHY -------------, Noakes, L.C., and Perry, W.J., 1953. Canberra 4 Mile Geological Sheet SI 55-16. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. Joyce, A.S., 1970a. Geochemistry of the Murrumbidgee Batholith, New South Wales. Ph.D. Thesis, Aust. natn. Univ., Canberra (unpubl.). 167 -----------, 1970b. Chemical variation in a pelitic hornfels. Chern. GeoZ., 6,51-58. -----------, 1973a. Chemistry of the minerals of the granitic Murrumbidgee Batholith, Australian Capital Territory. Chern. GeoZ., 11(4), 271-296. -----------, 1973b. Petrogenesis of the Murrumbidgee Batholith, A.C.T. J. geoZ. Soa. Aust., 20(2),179-197. Kennedy, D.R., 1966. Progress report. Exploration License No. 34, New South Wales. Rep. Anaaonda Aust. Inc. IR-155/16/1 (unpubl.) (GS 1966/082). -------------, Johnson, I.R., and Flack, D.S., 1963. Reconnaissance geological survey of the south-eastern portion of the Canberra 4-mile sheet. Rep. geoZ. Surv. N.S.W., GS 1963/128 (unpubl.). Kenny, E.J., 1923. Copper. BuZZ. geoZ. Surv. N.S.W., 3. 51 pp. ------------, 1924. Gold. BuZZ. geoZ. Surv. N.S.W., 7. 60 pp. ----------- and Mulholland, C. St J., 1939. Geological survey of Captain's Flat. Progress report. A. Rep. Dep. Mines N.S.W. for 1938, 102-103. ----------- and --------------------, 1940. The ore-deposits of Captain's Flat, New South Wales. Rep. geoZ. Surv. N.S.W., GS 1940/012 (unpubl.). ----------- and --------------------, 1941. The ore-deposits of Captain's Flat, New South Wales. Proa. AUBtraZas. Inat. Min. MetaZZ., 122, 45-62. Kolbe, P., and Taylor, S.R., 1966. Geochemical investigation of the granitic rocks of the Snowy Mountains area, New South Wales. J. geoZ. Soa. Auat., 13(1), 1-25. Lake George Mines Pty Ltd, 1900. Anembo Geological Map. PiZe geoZ. SUrv. N.S.W., GS 0000/013 (unpubl.). -------------------------, 1953. Geology of the Lake George mine at Captains Flat, in Geology of Australian Ore Deposits. RubZB 5th Emp. Min. MetaZZ. Congr., Aust. N.Z., 1, 910-920. (See also Glasson 1951, 1952; Maclaren 1928; Tyler 1947). Larson, R.A., 1972. Summary report, Burra prospect, Parish of Urialla, County Murray, New South Wales. Rep. Conwest (Aust.) N.L. (unpubl.) (GS 1972/42). Layton and Associates Pty Ltd, 1970. Prospects in the Cooma [-Bredbo] district, N.S.W. 1st report, ELs 239 and 308. Rep. for AZpex Ltd (unpubl.) (GS 1970/485). 168 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Legge, J.G., 1937. Notes on the physiography and geology of the Federal Capital Territory. Rep. Aust. N.Z. Ass. Advmt Soi., 23, 84-88. Link, A.G., 1970. Age and correlations of the Siluro-Devonian strata in the Yass Basin, New South Wales. J. geoZ. Soo. Aust., 16(2), 711-722. Lovering, J.F., and Richards, J.R., 1964. Potassium - argon age study of possible lower-crust and upper-mantle inclusions in deep-seated intrusions. J. geophys. Res., 69 (22),4895-4901. Lyon, R.J.P., 1949. The petrology of the acid volcanics at Captains Flat, N.S.W. B.So. Hons Thesis, Univ. West. Aust., Perth (unpubl.). McAlpine, J.R., and Yapp, G.A., 1969. Part IV. Climate of the Queanbeyan- Shoalhaven area, in Lands of the Queanbeyan-Shoalhaven Area, A.C.T. and N.S.W. Land Res. Ser. C.S.I.R.O., Aust., 24, 57-75. McClatchie, L., 1973. The occurrence of bismuth in the Lachlan Fold Belt in New South Wales. Proo. AustraZas. Inst. Min. MetaZZ., 248, 27-36. McInnes, G.E., 1949. The geology of the Canberra - Tharwa area. Reo. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1949/52 (unpubl.). and Jones, J.B., 1952. A geological reconnaissance of the southern portion of the Australian Capital Territory. Rea. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1952/10 (unpubl.). Maclaren, M., 1928. Geological report on Lake George mines, Captains Flat, N.S.W. Rep. to Lake George Mines pty Ltd (unpubl.). McLeod, I., 1962. Notes prepared to accompany a preliminary geological map of potential brick shale deposit, Googong. Rep. Bur. Miner. Resour. GeoZ. Geophys. Aust. (unpubl.) (GS 1962/138). -----------, (Ed.), 1965. Australian Mineral Industry: The Mineral Deposits. BuZZ. Bur. Miner. Resour. GeoZ. Geophys. Aust., 72. 690 pp. Mahony, D.G., and Taylor, C.T., 1913. Report on a Geological Reconnaissance of the Federal Territory, with special reference to available building materials. Govt Printer, Melbourne. Mitchell, J., and Dun, W.S., 1920. The Atrypidae of New South Wales, with references to those recorded from other States of Australia. Proo. Linn. Soo. N.S.W., 45(2), 266-276, pIs 14-16. Moye, D.G., Sharp, K.R., and Stapledon, D.H., 1963. Geology of the Snowy Mountains region. Rep. Snowy Mountains Hydro-EZeotrio Authority, Cooma, AustraZia (unpubL) . Nisbet, B.W., 1970. The structural geology of the Captains Flat area, New South Wales. B.Sa. Hons Thesis, Aust. natn. Univ., Canberra (unpubl.). SELECTED BIBLIOGRAPHY 169 Noakes, L:C., 1949. Geological notes on the proposed sites for a national reserve at Tidbinbilla and a zoological park in Canberra. Rea. Bur. Miner. Resour. Geol. Geophys. Aust., 1949/6 (unpubl.). ------------, 1957. The significance of high-angle reverse faults in the Canberra region. Rea. Bur. Miner. Resour. Geol. Geophys. Aust., 1957/2 (unpubl.). Nova Nickel N.L. (See Western Mining Corporation Ltd 1971, 1972, 1973, 1974a). Oocidental Minerals Corporation of Australia (See Faulkner 1975). Oldershaw, W., 1965. New South Wales. Geological and geochemical survey of the Captains Flat area, Rep. Bur. Miner. Resour. Geol. Geophys. Aust., 101. 55 pp. Opik, A.A., 1958. The geology of the Canberra City district. Bull. Bur. ~ner. Resour. Geol. Geophys. Aust., 32. 99 pp. Owen, M., Gardner, D.E., Wyborn, D., Saltet, J., Walton, D.G., Mifsud, J.M., and Cooper, R.D., 1974a. Tantangara 1:100,000 Geological Sheet 8626. Prelim. edn. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. ------, and Shackleton, M.S., 1974b. Geology of the Tantangara 1:100,000 sheet area, Australian Capital Territory and New South Wales. Rea. Bur. Miner. Resour. Geol. Geophys. Aust., 1974/176 (unpubl) • --------, , , and --------, in prep. Geology of the Tantangara and Brindabella 1:100,000 Sheets. BuZZ. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. and Wyborn, D., 1974. Tantangara - Brindabella mapping project, in Geological Branch summary of activities. Rea. Bur. Miner. Resour. Geol. Geophys. Aust., 1974/127, 22-24 (unpubl.). -----, -----, and Blythe, P., 1975. Brindabella 1:100,000 Geological Sheet 8627. Prelim. edn. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. Packham, G.H., 1960. Sedimentary history of part of the Tasman Geosyncline in south eastern Australia. Rep. 21st into geol. Congr., Copenhagen, 12, 74-83. ------------, 1962. An outline of the geology of New South Wales, in A Goodly Heritage: Science in New South Wales. A.P. Elkin (Ed.). Jubilee Handbook 36th Meet. Aust. N.Z. Ass. Advmt Sai., Sydney, pp. 24-35. (Ed.), 1969. The Geology of New South Wales. J. geol. Soa. Aust., 16(1). xx + 654 pp. Page, R.W., 1968. Catalogue of radiometric age determinations carried out on Australian rocks in 1966. Rea. Bur. Miner. Resour. Geol. Geophys. Aust., 1968/30 (unpubl.). Pedder, A.E.H., 1967. Devonian rocks of the Murrumbidgee area, New South Wales. Proa. into Symp. Devonian System, Alberta Soa. Petrol. Geol., 2, 143-146. 170 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Perriam, R., Rutter, H., Hayden, P., and Robins, T., 1975. Terminal report on Exploration Licence 476, Narongo, New South Wales. Rep. Western Mining Corp. Ltd, K/2094 (unpubl.) (GS 1975/236) • Phillips, J.R.P., 1952. Geology of the Queanbeyan district. B.So. Hons Thesis, Univ. Sydney, Sydney (unpubl.). -----------------, 1956. Geology of the Queanbeyan district. J. Proo. R. Soo. N.S.W., 89(2), 116-126. Pickett, J., 1971. Limestone samples from Canberra and Bega 1:250,000 sheet. Rep. geol. Surv. N.S.W., Pa1aeont. 1971/20 (unpub1.) (GS 1971/453). ------------------, 1972. Limestone samples from Captains Flat 1:50,000 sheet. Rep. geol. Surv. N.S.W., Pa1aeont.1972/16 (unpub1.) (GS 1972/229). Pidgeon, R.T., 1965. New South Wales. The geochronology of two regionally metamorphosed areas in Ph. D. Thesis, Aust. na,tn. Univ., Canberra (unpubl.). and Compston, W., 1965. The age and origin of the Cooma Granite and its associated metamorphic zones, New South Wales. J. Pet., 6, 193-222. Pi11ans, B., 1974. Surficial geology of the Murrumbidgee - Bredbo interf1uve with notes on the bedrock geology. B.So. Hons. Thesis, Aust. natn. Univ., Canberra (unpubL) • Piper, D.J.W., von Huene, R., and Duncan, J.R., 1973. Late Quaternary sedimentation in the active eastern Aleutian Trench. Geology, 1(1}, 19-22. Pogson, D.J., 1972. Geological Map of New South Wales, scale 1:1,000,000. Geo1. Surv. N.S.W., Sydney. and Baker, C.J., 1974. Revised stratigraphic nomenclature for the Yass 1:100,000 sheet. Q. Notes geol. Surv. N.S.W., 16, 7-9. Raggatt, H.G., 1929. The Anembo gossans. A. Rep. Dep. Mines N.S.W. for 1928, 132-133. Rattew, A.R., Finney, W., and Dowse, R.K., 1973. Interpretation report, airborne electromagnetic survey, Barringer "input" system, of the New South Wales areas of Miche1ago A, Miche1ago B, and Narongo. Rep. Geoterrex Ltd for Western Mining Corp. Ltd (unpub1.) (GS 1975/236). Richards, D.N., 1967. The geology of the Jerang1e district, New South Wales. B.So. Hons Thesis, Aust. natn. Univ., Canberra (unpub1.). Richardson, S.J., 1975. A summary of the geology of the Miche1ago 1:100,000 sheet. Q. Notes geol. Surv. N.S.W., 21, 1-7. and Sherwin, L., 1975. Early Silurian graptolites near Bredbo. Q. Notes geol. Surv. N.S.W., 21, 17-19. Rickard, M.J., 1961. A note on cleavages in crenu1ated rocks. Geol. Mag., 98(4), 324-332. SELECTED BIBLIOGRAPHY Roddick, J.C., and Compston, W., 1976. Radiometric evidence for the age of emplacement and cooling of the Murrumbidgee Batholith. J. geol. Soc. Aust., 23(3), 223-233. 171 Rose, G., 1962. reports) . Geological survey of Captains Flat (with relevant progress File geol. Surv. N.S.W., GS 1962/089 (unpubl.). RoSS, C.S., and Smith, R.L., 1961. Relations and Identification. Ash-Flow Tuffs: their Origin, Geologic ~of. Pap. U.S. geol. Surv., 366. 81 pp. Rowley, O.K., 1975. Potassium - argon age dating of seven samples from New South Wales. Rep. The Australian Mineral Development Laboratories, AN 3898/75 (unpubl.) (GS 1975/187). Scheibner, E., 1972a. Tectonic concepts and tectonic mapping. Rec. geol. Surv. N.S.W., 14(1), 37-83. -------, 1972b. Chairman's address. To rejector accept and modify the theory of plate tectonics? Tectonics and Structural Newsletter of the specialist Group in Tectonics and Structural Geology, geol. Soc. Aust., 1,2-13. -----------, 1974a. A plate tectonic model of the Palaeozoic tectonic history of New South Wales. J. geol. Soc. Aust., 20(4), 405-426. ------------, 1974b. Tectonic Map of New South Wales, scale 1:1,000,000. Geol. Surv. N.S~W., Sydney. Sedmik, E.C.E., 1965. Captains Flat Metalliferous Geophysical Survey, N.S.W., 1960. Rep. Bur. Miner. Resour. Geol. Geophys. Aust., 96. 13 pp. Seigel Associates Australasia Pty Ltd (See Irving 1971). Sharp, K.R., 1949. The general geology of the Michelago district. B.Sc. Hons Thesis, Univ. Sydney, Sydney (unpubl.). Sheppard, N., and Bates, C.D.S., 1971. Quarterly report No.7, Mineral Exploration Licence No. 239 lCooma - Bredbo area]. Rep. Amax Exploration (Aust.) Inc. for Alpex Ltd (unpubl.) (GS 1971/605). Sherra~d, K.M., 1939. The general geology of the district east of Yass, N.S.W. ~oc. Linn. Soc. N.S.W., 64, 577-600. --------------, ]954. The assemblages of graptolites in New South Wales. J. ~oc. R. Soc. N.S.W., 87(3), 73-101, pIs x-xi. 1962. Further notes on assemblages of graptolites in New South Wales. J. ~oc. R. Soc. N.S.W., 95(5), 167-178, pI i. Sherwin, L., 1971. Stratigraphy of the Cheesemans Creek district, New South Wales. Rec. geol. Surv. N.S.W., 13(4), 199-237. 172 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET -------------------, 1972. Silurian fossils from Cooma and Michelago. Rep. geol. Surv. N.S.W., Pa1aeont. 1972/24 (unpubl.) (GS 1972/361). ---------------, 1973a. Stratigraphy of the Forbes - Bogan Gate district. Rea. geol. Surv. N.S.W., 15(1), 47-101. ---------------, 1973b. Silurian fossils from the Bredbo district. Rep. geol. Surv. N.S.W., Pa1aeont. 1973/22 (unpubl.) (GS 1973/369). -------------------, 1974a. Silurian fossils from the Michelago district. Rep. geol. Surv. N.S.W., Pa1aeont. 1974/4 (unpubl.) (GS 1974/044). -------------------, 1974b. Ordovician and Silurian fossils from the Bredbo district. Rep. geol. Surv. N.S.W., Pa1aeont. 1974/10 (unpubl.) (GS 1974/092). -------------------, 1974c. Silurian fossils from the Colinton Volcanics at Bredbo. Rep. geol. Surv. N.S.W., Pa1aeont. 1974/17 (unpubl.) (GS 1974/128). -------------------, 1974d. Brachiopods from the Michelago district. Rep. geol. Surv. N.S.W., Pa1aeont. 1974/25 (unpubl.) (GS 1974/298). -------------------, 1974e. Ordovician and Silurian fossils from the Bredbo- Michelago district. Rep. geol. Surv. N.S.W., Palaeont. 1974/35 (unpubl.) (GS 1974/444). -------------------, 1975a. Glaciation and the Benambran Orogeny. Q. Notes geol. Surv. N.S.W., 18, 13-18. -------------------, 1975b. Monograptus from Colinton Hill. Rep. geol. Surv. N.S.W., Pa1aeont. 1975/2 (unpubl.) (GS 1975/034). Simpson, G.B., 1972. Geology of the Googong Reservoir, Queanbeyan River, N.S.W. Bea. Bur. Miner. Resour. Geol. Geophys. Aust., 1972/18 (unpubl.). Slansky, E., 1973. The identification of a white clay from east of Burra-Michelago road. Rep. geol. Surv. N.S.W., Minera1og. 1973/34 (unpubl.) (GS 1973/252). Slepecki, S., 1973. An introduction to the Jerang1e Complex. B.Sa. Hons Thesis, Univ. Sydney, Sydney (unpubl.). Smith, E.M., 1963. Notes on prospecting and m~n~n9 in the Australian Capital Territory and environs. Rea. Bur. Miner. Resour. Geol. Geophys. Aust., 1963/110 (unpub1.). Snelling, N.J., 1957. The geology and petrology of the Murrumbidgee Batholith and its relation to the Palaeozoic igneous activity of the Tasman Geosyncline. Ph. D. Thesis, Aust. natn. Univ., Canberra (unpubl.). -------------, 1960. The geology and petrology of the Murrumbidgee Batholith. Q. Jl geol. Soa. Lond., 116(2), 187-217. Snowy Mountains Hydro-Electric Authority (See Moye, Sharp, and Stapledon 1963). SELECTED BIBLIOGRAPHY Stauffer, M.R., 1964. Multiple folding and deformation of Lower Palaeozoic rocks near Queanbeyan, New South Wales. Ph. D. Thesis, Aust. natn. Univ., Canberra (unpubl.). --------------, 1967a. The problem of conical folding around the Barrack Creek Adamellite, Queanbeyan, New South Wales. J. geoZ. Soa. Aust., 14(1), 49-56. --------------, 1967b. Tectonic strain in some volcanic, sedimentary, and intrusive rocks near Canberra, Australia: A comparative study of deformation fabrics. N.Z. JZ GeoZ. Geophys., 10(4), 1079-1108. and Rickard, M.J., 1966. The establishment of recumbent folds in the Lower Palaeozoic near Queanbeyan, New South Wales. J. geoZ. Soa. Aust., 13(2), 419-438. --------------, Wilson, E.G., and Crook, K.A.W., 1964, Notes on the geology of the Cullarin Horst and environs, in Geological Excursions, Canberra District, pp. 43-47. Bur. Miner. Resour. Geol. Geophys. Aust., for Aust. N.Z. Ass. Advrnt Sci. Meeting, Canberra. Stevens, B.P.J., 1973. Barite deposits in the Captains Flat - Jerangle area. Rep. geoZ. SUrv. N.S.W., GS 1973/246 (unpubl.). Stevens, N.C., 1957. Further notes on Ordovician formations of central New South Wales. J. Proc. R. Soa. N.S.W., 90(2), 44-50. Story, R., 1969. Vegetation of the Queanbeyan - Shoalhaven area, in Lands of the Queanbeyan - Shoalhaven Area, A.C.T. and N.S.W. Land Res. Ser. C.S.I.R.O. Aust. 24, 113-133. 173 Strusz, D.L., 1968. Bibliography of the geology and geomorphology of the Canberra 1:250,000 sheet. Rea. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1968/94 (unpubl.). ------------, 1971. Explanatory Notes on the Canberra 1:250,000 Geological Sheet SI 55-16. 47 pp. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. ------------, 1972. Correlation of the Lower Devonian rocks of Australasia J. geoZ. Soa. Aust., 18(4), 427-455. and Henderson, G.A.M., 1971. Explanatory Notes on the Canberra City, A.C.T., 1:50,000 Geological Sheet. 20 pp. Bur. Miner. Resour. Geol. Geophys. Aust., Canberra. Sullivan, C.J., 1946. Barite deposit -- Harold's Cross, Captains Flat district. Rea. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1946/18 (unpubl.). Sussmilch, C.A., 1910. New South Wales. Notes on the physiography of the Southern Tablelands of J. Proa. R. Soa. N.S.W., 43, 331-354. Taylor, T.G., 1923. Geography of Canberra region, in Excursion to Yass - Canberra and the Murrumbidgee Irrigation Area. Guidebook Pan-Paaif. Sai. Congo Meeting J VI, Sydney, pp. 1-9. 174 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Tenneco Australia Inc., 1972. Quarterly reports Nos 8-12, EL area -- with Amax Exploration (Aust.) Inc for Alpex Ltd. N.S.W., GS 1972/409 (unpubl.). 239, Cooma - Bredbo FiZe geoZ. Surv. ----------------------, 1973. Diamond drilling aid, EL 308, Michelago and Colinton prospects. FiZe geoZ. Surv. N.S.W., GS 1973/138 (unpubl.). (See also Besley 1972a, b). Thomas, D.E., 1960. The zonal distribution of Australian graptolites; with a revised bibliography of Australian graptolites. J. Froa. R. Soa. N.S.W., 94(1), 1-58. Toghill, P., 1970. Highest Ordovician (Hartfell Shale) graptolite faunas from the Moffat area, south Scotland. BuZZ. Br. Mus. (nat. Hist.), Geo1. 19(1), 1-27, pls 1-16. Tyler, E.W.J., 1949. The heavy mineral assemblages in a group of sediments from Captains Flat. B.Sa. Hons Thesis, Univ. West. Aust., Perth (unpubl.). (fide Glasson 1957). Tyler, W.H., 1947. Geological report on the Lake George mine. Rep. to Lake George Mines Fty Ltd (unpubl.) (fide Glasson 1957). Vallance, T.G., 1966. A contact metamorphic axinite paragenesis at London Bridge, near Queanbeyan, N.S.W. J. Froa. R. Soa. N.S.W., 99, 57-67. --------------, 1969. Southern and Central Highlands Fold Belt: Plutonic and metamorphic rocks, in The Geology of New South Wales. J. geoZ. Soa. Aust., 16(1), 180-200. Veevers, J.J., 1951. The regional geology and stratigraphy of an area north-west of Captains Flat, N.S.W., with a short account of the sedimentary and contact metamorphic phenomena at London Bridge, N.S.W. B.Sa. Hons Thesis. Univ. Sydney, Sydney (unpubl.). -------------, 1952. Geology of Canberra 4-mile. Rep. Bur. Miner. Resour. GeoZ. Geophys. Aust. (unpubl.) (GS 1953/55). -------------, 1953a. The London Bridge Limestone, Monaro district, New South Wales. Rea. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1953/55 (unpubl.). -------------, 1953b. Geology of the eastern part of the Canberra 4-mile sheet. Rea. Bur. Miner. Resour. GeoZ. Geophys. Aust., 1953/99 (unpubl.). Voisey, A.H., 1958. Further remarks on the sedimentary formations of New South Wales. J. Froa. R. Soa. N.S.W., 91(4), 165-188. ------------, 1959. Australian geosynclines. Aust. J. Sai., 22(5), 188-198. von Huene, R., 1972. Structure of the continental margin and tectonism at the eastern Aleutian trench. BuZZ. geoZ. Soa. Am., 83(12), 3613-3626. SELECTED BIBLIOGRAPHY 175 Walker, R.G., and Sutton, R.G., 1967. Quantitative analysis of turbidites in the Upper Devonian Sonyea Group, New York. J. sedim. Pet., 37(4), 1012-1022. Wallace, I., 1969. Building Stones of New South Wales. Monogr. Dep. Industrial Arts. Univ. N.S.W.• Sydney, 1(2). 73 pp. Walpole, B.P., 1964. Notes on the Brindabella - Cooleman Caves - Tantangara - Yaouk Excursion, in Geological Excursions, Canberra District pp. 35-42. Bur. Miner. Resour. Geol. Geophys. Aust., for Aust. N.Z. Ass. Advrnt Sci. Meeting, Canberra. Webby, B.D., 1972. Devonian geological history of the Lachlan Geosyncline. J. geol. Soo. Aust., 19(1), 99-123. Wellman, P., 1971. The age and palaeomagnetism of the Australian Cenozoic volcanic rocks. Ph. D. Thesis, Aust. natn. Univ., Canberra (unpubl.). and McDougall, I., 1974. Potassium - argon ages on the Cainozoic volcanic rocks of New South Wales. J. geol. Soo. Aust., 21(3), 247-272. Western Mining Corporation Ltd,197l. Progress reports Nos 1-7, EL 438, Queanbeyan area -- for Nova Nickel NL. File geol. Surv. N.S.W.• GS 1971/653 (unpubl.). -----------------------------, 1972. Exploration reports Nos 1-7, EL 476, Captains Flat, Jerangle, Umeralla areas -- for Nova Nickel NL. File geol. Surv. N.S.W., GS 1972/093 (unpubl.). -----------------------------, 1973. Exploration reports, EL 538, Captains Flat- Bungendore areas. File geol. Surv. N.S.W., GS 1973/265 (unpubl.). -----------------------------, 1974a. Drilling aid, Googong prospect, EL 438, Queanbeyan. File geol. Surv. N.S.W., GS 1974/097 (unpubl.). -----------------------------, 1974b. Drilling aid. PL's 343 and 345, Cooma, Clare prospect, Bungendore. File geol. Surv. N.S.W., GS 1974/404 (unpubl.). -----------------------------, 1975. Exploration Licence No. 694. Terminal report [Royalla - Burra area]. Rep. Western Mining Corp. Ltd (unpubl.) (GS 1975/041). (See also Perriam et al. 1975, Rattew et al. 1973). White, A.J.R., Chappell, B.W., and Branch, C.D., 1964. Classification of granite types according to associated rocks. Abstr. 37th Congr. Aust. N.Z. Ass. Advmt Soi., Canberra. --------------, and Cleary, J.R., 1974. Geologic setting and emplacement of some Australian Paleozoic batholiths and implications for intrusive mechanisms. Paoif. Geol., 8, 159-171. White, D.A., 1962. Review of the age determination programme of the Bureau of Mineral Resource's, Australia 1956-1962. Reo. Bur. Miner. Resour. Geol. Geophys. Aust., 1962/129 (unpubl.). 176 Whitten, G.F., 1952. New South Wales. (GS 1952/040). GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Final report on Anembo copper - zinc prospect, Cooma Division, Rep. EZeat!'oZytia Zina Co. of A/asia Ltd. 25 (unpubl.) Whitworth, H.F., 1929. Petrological descriptions of rocks forwarded by the Chief Inspector of Mines from Captains Flat. A. Rep. Dep. Mines N.S.W. for 1928, 108-110. Williamson, W.H., 1949. The petrology and general geology of an area south of Captain's Flat, N.S.W. B.Sa. Hons Thesis. Univ. Sydney. Sydney (unpubl.). Wilson, E.G., 1960. Thin sections of rocks from the Australian Capital Territory and environs prepared between 1947 and 1959. Rea. Bu!'. Mine!'. Resouro. GeoZ. Geophys. Aust•• 1960/93 (unpubl.). Woolnough, W.G., 1939. Geology and physiography of the Australian Capital Territory and surroundingareas, in Handbook for Canberra. K. Binns (Ed.). Handbook 24th Cong!'. Aust. N. Z. Ass. Advmt Sai .• Canbe!'!'a. pp. 111-118. Young, C.H., 1974a. Final report, Exploration Licence Nos. 239 and 308 (Cooma- Michelago area). Rep. Cominao Exp Zo!'ation pty Ltd foro AZpe:x: Ltd (unpubl.) (GS 1974/347). ------, 1974b. Relinquishment report, EL's 239 and 308, Cooma - Michelago area. Rep. Cominao ExpZoration pty Ltd foro AZpe:x: Ltd (unpubl.) (GS 1974/463). APPENDIX 1 FOSSILS RECORDED FROM THE MICHELAGO 1:100,000 SHEET AREA Foxlow Beds •• •• Ryrie Formation • • • • • • Cappanana Formation Colinton Volcanics Bransby Beds Copper Creek Shale •• Captains Flat Formation.. .• •• •• •• 178 •• 183 •• 185 •. 196 •• 198 •• 200 ., 200 //1111111111111111111111111111111111111111111111111111111111 D004942090 Map No. Locality Lithology Fossils recorded Foxlow Beds Comments ..... -oJ CD 2 Captains Flat 205590 Highly Nesog1'CIptus cf muZtidens Late Sherrard Railway Station compressed Cf Orthograptus Ordovician 1954 blue slate caZcaratus var. acutus dipping west Cryptograptus tricornis at 85· (Carruthers) Nemagraptus pertenuis 2A 205590 Graphitic Mesograptus muZtidens Zones 10-12 Oldershaw black shale Nemagraptus tricornis (Gisbornian) 1965 Dicranograptus cZingani Late CUmacograptus bicornis Ordovician Leptograptus sp. DiceZZograptus sp. 4 South of Captains 194491 possible CUmacograptus Zone 12 (?) = Williamson Correlates with: Coolringdon Beds at Flat on roadside bicornis top of 1949 Cooma (Joplin 1942, p. 160), 3 km south of CZimacograptus caudatus Australian uMundoonen Series II near Yass Ballinafad Creek CZimacograptus cf brevis Eastonian - (Sherrard 1939, p. 580) . crossing DipZograptus sp. picranograptus cZingani Zone 4A 10.5 km south of 194491 Blue slate Dicranograptus hians Late Sherrard Captains Flat on CZimacograptus sp. cf Eastonian - 1954 the Jerangle C. bicornis Latp. Packham road, parish C. caudatus Lapworth Ordovician 1969 Jinjera, County C. sp. cf C. minimus Murray, Portion (Carruthers) 34 - Captains Flat - Black shale Mesograptus afL Zone 10 = Glasson The existence of such a species as area muZtidens (Elles and base of 1952, 1957 Nemagraptus tricornis is subject to Wood) Australian Veevers doubt. Nemagraptus tricornis Eastonian - 1951 (Carruthers) Late Ordovician 6 Near fault(?) 999140 Blue/black Dicranograptus sp. Gisbornian Hancock Collection is small and consists of to south of shale/slate to 1963 graptolites preserved as relief Bredbo River Eastonian impressions in very strongly silicified and to east of shale. Apart from a dozen or so "Cappawidgee" fragments there is a single well- homestead, a few preserved Dicranograptus. hundred metres south of the creek and south of the main track ..... ..... o o o o o en ::t: t'l t'l ..;J 7 To the south 002156 Bluish slate Dicranograptus cf Late Sherwin of Bredbo brevicaulis Ordovician = 1974b River in Mesograptus cf multidens Gisbornian third dam Clinr:zcograptU8 bicornis (Thomas CZimacograptus sp. 1960) 8 Near Ordovician 001159 8lack shale CZimacograptus bicornis Late Horner Silurian Eastonian 1973 contact to south of Bredbo River 9 At the junction 010168 Black chert Cryptograptus tricornis Late Sherwin of Bredbo O1'tllOgraptus Ordovician 1974b River and qua.drimucronatus Strike-A-Light River 11 North of Bredbo 997174 Black shale CZimacograptus bicornis Eastonian ANU River near DiceUograptus sp. 1974 Cappanana Creek 23 Small shallow 996206 Silicified DiceUograptus sp. Late Hancock A few graptolites are visible on the quarry 20 m blue black DipZograptus sp. Ordovician 1963 bedding planes which coincide with the from Bredbo - shale direction of preferential splitting, Jerangle road, but their preservation is very poor. opposite Only two specimens have been identified turnoff to generically -- DiceZZograptus and Crimmins DipZograptus -- and none specifically. shearing shed, in Cappanana Creek valley 25 Bredbo - Jerangle 001209 Dark-grey CZimacograptus sp. Possible Sherwin This age determination is dependent road to east shale band ?Gl.yptograptus cf Early 1974b upon the identification of an of Cappanana serratus Silurian incompletely preserved glyp~ograptid. Creek in road (Zones Refer No. 25A for more detailed cutting 19-21) collection. 25A Road cutting 001209 3 cm wide DiceZZograptus cf Late Sherwin This assemblage clearly indicates a to east of blackish omatus minor Ordovician 1974e Late Ordovician age, but the deformed Cappanana shale band Toghill and fraqmentary condition of the Creek on Bredbo CZimacograptus sp. dicellograptids makes unequivocal Jerangle road determination at species level uncertain. In the type Late Ordov ician - Early Silurian graptolite sequence at Dobbs Linn, D. ornatus minor occurs within the top 5 m of Ordovician strata (Toghill 1970). Map Locality Grid Lithology Fossils recorded Age Reference Comments No. ref. 26 On Bredbo- 007212 Siltstone CZimacograptus sp. Late Sherwin The fragmentary condition makes the Jerangle road ?Leptograptu8 sp. Ordovician 1974b identification of Leptograptu8 near Scheele's uncertain but a Late Ordovician age house is favoured. 47 Gungoandra Gap, 983246 Black shale Climacograptus sp. Late ANU further to east Ordovician 1973 (Gisbornian?) 48 To the east of 982246 Black shale Climacograptus bico17lis Ordovician ANU Gungoandra Gap peltifer 1974 Orthograptus sp. 60 Northeast of 980252 Dicellograptus cf Ordovician Sherwin The graptolites at this locality are Gungoandra Gap o17latus minor 1974e fragmentary and poorly preserved Climacograptu8 sp. because of the combined effects of cleavage and weathering. The age indicated is Late Ordovician. 60A 980252 Black shale Climacograptus bico17lis Ordovician ANU peltifer 1974 Dicellograptus sp. Orthograptus sp. (Thomas 1960) 61 Side creek off 979255 Black/blue Dice llograptus camp lanatu8 Latest S.K. Skwarko The fossil assemblage is moderately headwaters of slate/shale o17latus Elles and Eastonian in Hancock rich, and consists of compressed Colyers Creek. Wood 1904 1963 biserial and manaserial graptolites. Right-hand creek Dicranograptus hians Many of the graptolites are poorly going downstream T.S. Hall 1905 preserved. Dicranograptus ? nicholsoni Hopkinson 1847 Dicranograptus sp. cf D. ramosus J. Hall 1874 CZimacograptus bico17lis J. Hall 1847 Climacograptus juvenile and immature species Diplograptid fragments Retiograptus yassensis Sherrard and Keble 1937 ..... !Xl o ~ o ~ o ".l t-3 gj :;: H () :x: t<:l ~ ..... ..... o o o o o (J) :x: t<:l t<:l t-3 61A In Ordovician 979255 cZin:atJograptulJ caudatus Late ANU to northeast CZUr~ograptus bicornis Eastonian 1973 of Gungoandra CI'YP tograptulJ tl'icornis Gap Orthagraptus ca Zcaratus. 618 In Ordovician to 979255 CZin:atJograptus caudatus Late ANU northeast of CZin:atJograptus sp. Eastonian 1973 Gungoandra Gap I>icranograptus sp. c f ramosus ZongicauZis 64 980261 81ack shale Dicranograptus hians Ordovician ANU Orthagraptus sp. 1974 I>icranograptulJ ramosus spirifer Neurograptus fibratus CZin:atJograptus missHis I>iceZZograptus caduceus CZin:atJograptus bicornis 64A 980261 Black shale CZin:atJograptus missi Zis Ordovician ANU DiceZZograptus caduceus (early to 1974 CZin:atJograptus bicornis middle Zongispinus Bolindianl? 648 980261 CZima.cograptus missiZis Ordovician ANU Dice ZZograptus (early 1974 forchamneri {Zexuosus Eastonian to Orthagraptuspageanus early spinosus Bolindianl 65 981264 I>icranograptus ramosus Ordovician ANU spinifer (early 1974 Neurograptus fibratus Eastonian to CZin:atJograptus bicornis early Orthagraptus caZcaratus Bolindianl acutus 73 Colinton Hill 990285 ? Orthagraptus Late ANU Cryptograptus tricornis Eastonian 1973 CZin:atJograptus bicornis I-- Q) I-- Map Locality Grid Lithology Fossils recorded Age Reference Comments NO. ref. 73A Colinton Hill 990285 Blue slate Dice Hograptus affinis Late Sherwin Poor preservation makes identifications and black DicellograptuB cf Ordovician 1974b uncertain but a definite Late Ordovician chert caduceus age is indicated, probably younger than Dicellogroptus cf the assemblage No. 83. This locality is forcharruneri probably equivalent to that from which Climwogroptus cf the Stockyard Creek fauna was collected tubuli ferus (Hall 1902). Orthogroptus fo liaceus sensu Hall Orthogroptus spp. (=7apiculatus) 72 Colinton Hill 988285 Black shale Dicranograptus hians (Ordovician) ANU Climacograptus exiguus late 1973 Dicranograptus sp. East.onian 74 Colinton Hill 990289 Black shale Graptoli tes (poor Late ANU preservation, not Eastonian (7) 1973 identified) 76 Colinton Hill 990292 Black shale Climwograptus exiguus Ordovician ANU C. tubuli f erus 1973 Dicranograptus hians Dice Hograptus sp. cf corrrplanatus ornatus Orthogroptuscalcaratus basiliaus O. calcarotus Cryptogroptus sp. 81 To north of 967354 Orthograptus sp. Ordovician ANU "Willandra" 1973 homestead 82 To north of 965364 Black slate Dicranogroptus sp. cf Ordovician ANU "willandra ll D. ram08US 1973 homestead longicaulis 88 Near Ryrie 960380 Orthograptus sp. Ordovician (7) ANU Trig. Station 7 Amplexograptus sp. 1974 ...... ...... o o o o o (J) P:: t<:l t<:l 1-3 89 Near Ryrie 962382 CZir..acograptus sp. Ordovician ANU Trig. Station Orthogz'aptus sp. 1974 Leptograptidae DiceZZograptus foreharm:eri fZsxuosus 96 To west of 972404 C1'!fptograptus tricomis Ordovician - ANU "Micaligo" CZimacogz'aptus caudatus Eastonian(?) 1973 homestead 01'thogz'apt! ::r:: t'l t'l t-3 • 44 Cappanana Creek 976238 Shale EncI'in= sp. Late ANU Scutellids Silurian 1974 Pentamerid brachiopods AtP!fpa sp. Spiriferid brachiopods Gastropods Rugose coral (TPypLasma Favosites sp. sp.?) HeUoUtes sp. PhauLactis sp. 43 East of 979237 Arenite Atrypa sp. Late ANU Cappanana Creek HoweHeUa nucul.a Silurian 1974 EncI'in= sp. Crinoids Rugose corals Gastropods 42 Near Cappanana 981237 Arenite Crinoid fragments Late ANU Creek Silurian 1974 45 981240 Shale/ EncI'inW'Us sp. Late ANt; limestone AtP!fpina sp. Silurian 1974 Coelospirid sp. indet. Fardenia sp. Crinoid stems 46 982243 Shale EncI'inW'Us sp. Late ANU limestone Silurian 1974 51 To west of 977244 Arenite EncI'inW'Us sp. Late ANU the silver Brachiopods Silurian 1974 mine 52 Near 974244 Arenite Crinoid fragments Late ANU Gungoandra Gap Silurian 1974 53 Gungoandra Gap 973244 Arenite Davidsoniacea sp. indet. Late ANU Silurian 1974 54 Gungoandra Gap 971246 EncI'inW'Us sp. cf Late ANU mitcheUi Silurian 1973 Streptel.asma sp. Crinoids 54A 971246 Arenit,y Crinoid fragments Late ANU minor shale Silurian 1974 ~ \0 ~ Map Locality Grid Lithology Fossils recorded Age Reference Comments No. ref. 54B Por. 46 and 53 971246 Very impure CyathopyZZwn (cf Silurian Brown Ph Gungoandra, greyish shearsbyi) 1928 Co. Beresford; green TrypZasTTrl ZonsdaZei just east of limestone TrypZasma vermiformis upper reaches with Favosites gothZandicus of Colyers Creek subordinate Favosites goZdfussi pure and HaZysites austraZis massive HeZioZites minuta strata. Stl'OTTrltopora sp. Partial Stromatoporoid sp. indet. replacement by Actinoceras sp. haematite and CaZymene sp. magnetite. Encrinurus cf tubercuZosa Associated Crinoid stems grey shale, mudstone, and pale yellow and pink sandstone 62 971254 Howe ZZe ZZa cf nucuZa Late Sherwin This particular brachiopod is common in Barrande Silurian 1974e Late Silurian sediments in New South Wales. 63 To east of 971254 StrepteZasma sp. Silurian ANU Cappanana Crinoid stems (Ludlovian) 1973 Creek 63A 971254 Arenite! Pentamerus sp. Late ANU minor shale Silurian 1974 66 966265 Crinoidal debris Late ANU Encrinurus sp. cf Silurian 1973 E. mitcheZZi 67 967267 Arenite Crinoid fragments Late ANU Silurian 1974 68 965269 Shale Encrinurus sp. Late ANU Brachiopods Silurian 1974 Gastropods 69 966271 Arenite Atrypa sp. Late ANU Crinoid fragments Silurian 1974 . ..... ..... a a a a a til ::t: t>:l t>:l t-3 70 9&5277 Dark shale HOUJeUeZla sp. Late ANU Other workers locate this fossil Silurian 1974 further south. 77 To west of 970299 Limestone T1>yplasma sp. Could be ANU "Collingwood" Halysites sp. late 1974 homestead Corals of subfamily Wenlockian Pachyporinae 78 To south of 972329 Deformed Spinat!'!fpa sp. Late ANU Ingelara and highly Silurian 1974 Creek foliated brown shale dipping steeply west. Fractures in angular blocks 79 To north- 972332 Goniophoro sp. Late ANU west of Gastropcda indet. Silurian 1973 "Collingwood" homestead 79A To north- 972332 Stropheodontid sp. indet. Silurian ANU west of Athyrisinidae sp. indet. Ludlovian) 1973 IICollingwQod" homestead 85 To immediate 954381 HOUJeUella sp. Late ANU east of Inadunate crinoid calyx Silurian 1973 Monaro and debris Highway Stick-type polyzoans Melletidae? sp. indet. 90 958387 Acanthohalysites sp. Late ANU Silurian 1974 91 In creek to 9&3389 Brown mud- ?Lingula sp. Late Sherwin Fauna probably led a burrowing northwest of stone, Proectenodonta victoriae Silurian 1974a existence or, in the case of Ryrie Trig. bedding not (Chapman) Lingula, lived in a vertical burrow. Station well developed Parocyclas sp. ?Nuculana sp. Map Locality Grid Lithology Fossils recorded Age Reference Corranents No. ref. 9lA Approximately 963389 Brown HoweUeUa sp. Late Sherwin These two genera of brachiopods 3 m lower in mudstone, Aegil'ia sp. Silurian 1974a would have possessed pedicles which sequence than slightly Crinoid stems required a reasonably firm substrate, preceding coarser with or other secure means of attachment. locality much better developed bedding than No. 91 92 To east of 965393 H(}l,)eUeUa sp. Ludlovian ANU Monaro 1974a Highway 94 To east of 964399 Limestone Brachiopod (subfamily Middle to ANU Monaro Pentamerinae) Late 1973 Highway near Silurian railway line 94A Limestone 964399 Limestone Well-preserved fossil Silurian (7) Sharp north of remains 1949 Ryrie Trig. Station 94B 964399 Limestone Coral family 7.Hallidae Middle to ANU Genus 7 PhauZactis Late 1972 Silurian 94C 5 Jon south of 964399 Massive and CyathophyZZum sheaPsbyi Silurian Brown Michelago and characteris- TrypZasma cf vermiformis 1928 120 m east of tically Favosites gothZandicus railway 'line weathered limestone, small outcrop elongated parallel strike; fossils poor 95 To southeast 967405 TrypZasma sp. Late ANU of tlPonderose tl Silurian 1974 homestead I-' I-' o o o o o fJl :x: t'l t'l >-3 - Co1yers Creek - Limestone CyathophyUwn cf shearsbyi Late Veevers Tryptasma ZonsdaZei Silurian 1953a T1'yptasma vermiformis Favosites goth~icus Favosites gotdfussi HaZysites austraZis HeZioZites minuta Stromatopora sp. A stromatoporoid Crinoid stems Actinoceras sp. CaZymene sp. Encrinurus sp. - Bredbo River - Limestone(?) Favosites sp. Late Veevers Favosites goth Zandicus Silurian 1953a HaZysites Zithostrotionoides HeZioZites daintreei MUZtisoZenia tortuosa - 3 km south- - Limestone CyathophyUwn shearsbyi Late Veevers east of T1'ypZasma cf verm[.formis Silurian 1953a Livingstone Favosites goth~iCU8 Determin- Trig. Station ation by w.s. Dun from fauna collected by H.B. Brown (refer Brown 1928) - Near - Limestone Favosites sp. Late Veevers "Collingwood" PycnostyZus ? sp. nov. Silurian 1953a homestead - Outcrop at - Fine-grained Collected but unidentified Silurian Sharp divide diopside - 1949 between wollastonite Margarets limestone - Creek and "Surra" Surra Creek Limestone" Map No. Locality Lithology Fossils recorded Corrments Colinton Volcanics 14 Near "Bredbo" 979187 Calcareous Atrypoidea austpaZis Late Sherwin shearing shed nodules in Silurian 1974b siltstone 13 To east of 979187 Siltstone Encrinu:rus Late Sherwin Atrypoidea is very abundant and occurs Connellys Gap ?CZavofabeZZa sp. Silurian 1974b in a variety of growth stages. The Atpypoidea austraZis crushing of all larger valves suggests HowelleZZa sp. compaction before the sediment had consolidated. 55 West of 967247 Shale/ Pentamel'U8 sp. Late ANU Gungoandra minor Crinoid fragments Silurian 1974 Gap limestone 56 West of 966250 Shale/ Pentamel'U8 sp. Late ANU Cappanana minor Crinoid fragments Silurian 1974 Creek limestone 58 On Gungoandra 929250 Cleaved Favosites sp. Silurian, Sherwin Poorly preserved as m:>Ulds. Definite age Creek siltstone ? AZveoUtes sp. probably 1974c difficult to decide but the large pentamerid, and shale Small solitary rugose Late possibly Kipkidium, favours a Silurian age. corals, gen. et sp. indet Silurian The fauna is quite similar to well-preserved ? Isorthis sp. Late Silurian faunas further south at Quidong. ? Kirkidiwn sp. The fossils are disarticulated and associated Scutellum sp. s. I. with limestone pebbles. Crinoid stems 57 Gungoandra 922252 Impure llercophyZZwn shearsbyi Early Browne Creek I" km limestone (Sussmilch) Late 1944 south of "CystiphyZZwn" sp. Silurian Colinton Mucophy ZZum crateroides Gorge Eth. fiI. Favosites aZZani Jones 93 To east of 960400 Unidentified brachiopod Late ANU Monaro fragments Silurian(?) 1974 Highway - - Sandstone, HoweZZeZla angustipZicata Late Horner siltstone, MesophoZidostrophia nitens Silurian 1973 and mudstone; Encz>inu:t'Us cf mi tahe ZZi (Ludlovian) greenish grey, medium to fine grained - Railway - Limestone Favosites sp. Early Browne cutting 4 km ellipsoids A small orthid Late 1944 north of in tuff Silurian(?) Bredbo, near "Scottdale" homestead 101 On track 938420 Brown At1'lfpa cf reticuZaz>is Late Sherwin Specimens very similar to the above were leading to siltstone Linnaeus Silurian 1974e recorded by Mitchell and Dun (1920) from Cotters Late Silurian strata near Vass. Crossing 100 To immediate 963419 Crinoid debris Silurian ANU east of Brachiopod fragments 1974 Goulburn - Bombala railway line, south of Michelago 104 To southeast 969428 Fossil fragments - Late ANU of Michelago brachiopods Silurian 1974 iron quarry 106 To east of 969431 MaaropZeura spo Wenlockian ANU Michelago to 1974 iron quarry early Ludlovian 105 Near Michelago 967431 Encrinu:t'Us cf etheridgei Late Sherwin copper prospect Mitchell Silurian 1972 Subfamily Phacopinae, gen. et sp. indeto ? NickZesopora spo ? FistuZipora spo ? Hemit1'lfpa spo Solitary rugose corals indeto Map Locality Grid Lithology Fossils recorded Age Reference Comments No. ref. 116 Near "Spring 003527 Limestone Crinoids Silurian Sharp Valley" outcrop 1949 homestead on considerably Burra road sheared; finely crystalline; contains detrital quartz, sericite, and chlorite 118 To south of 912693 Coarse (1) Homosospiro sp. Late Sherwin Fauna fragmentary. Some larger blocks Tharwa - siliceous (1) Leptostrophia sp. Silurian 1974d from this locality give impression that Canberra sediments - (1) HOliJsZZsZZa sp. the fossils are concained within mud road mud clasts clasts. within a tuffaceous sandstone Bransby Beds 80 Near 925349 Grey-brown Indet. crinoid ossicles Late Sherwin Murrumbidgee siltstone, Silurian (?) 1974b River, slate II Ingelara" homestead 103 Near Cotters 926422 Favositss sp. Late ANU Crossing on Silurian 1974 west bank of Murrumbidgee River 102 Cotters 930420 Limestone Favositss sp. Late Sharp Crossing on Crinoid stems Silurian 1949 eastern bank of Murrumbidgee River .... ID (Xl .... .... o o o o o CJl :I: t'l t'l >;3 109 The "Marble 932451 Limestone Crinoidal limestone with Late Sharp Mine simple rugose corals Silurian 1949 Limestone" Crinoidal limestone with HeZioZites sp. and simple rugose corals ? HeZiolites sp. or Plasrr.oporo sp. Crinoidal limestone with? Cystiphyllum Fragments of coral Favosites sp. 110 At the mouth 933474 Limestone Favosites sp. Silurian Sharp of Micaligo T1yplasma sp. 1949 Creek Stromatoporoids Crinoid stems 111 Outcrop 0.4 km 933477 Limestone Favosites sp. Silurian Sharp north of Crinoid stems 1949 Micaligo ereek 112 East bank of 933483 Limestone. ? Fine Favosites sp. Silurian Sharp the All (fine corallites) 1949 Murrumbidgee specimens HeZioZites River somewhat ? Favosites sp. marmorized Indet. tabulates ? Spongophyllwn sp. Large simple rugose coral Indet. stromatoporoids Crinoid stems (up to 20 mm diameter) 113 East bank 934497 Specimen Favosites sp. (marmorized) Silurian Sharp of the collected 1949 Murrumbidgee from tuff River 2.4 km on almost north of the same Micaligo horizon Creek as.the limestone 114 North bank of 929512 Limestone Favosites sp. Silurian Sharp Murrumbidgee 1949 River Map Locality Grid Lithology Fossils recorded Age Reference Comments No. ref. 115 "Hanging 930522 Limestone HeUolites sp. Silurian Sharp Rock Limestone" Favosites sp. 1949, belt 0.8 km ? Section of pentamerid Carne and north-northeast Favosites sp. Jones 1919 of Hanging Rock. ? TPyplasma Hanging Rock A compound rugose coral- 7 km northwest possibly Disphyllum of Michelago Railway Station, Pore 128, Par. Monkellan, Co. Murray 117 On "Lanyon", 894678 Grey Lin(JUla sp. s.l. Ranges Sherwin Well preserved --but suggests brackish to south of (carbon- Ordovician 1974d rather than marine environment. Tharwa - aceolls?) to Holocene Canberra road siltstone but most likely Devonian Copper Creek Shale 1 9 kIn north 215672 Limestone Hercophyllu~ shearsbyi Silurian Glasson of Captains 1952, Flat Railway 1957; Station on Veevers main road 1951 5 Near Anembo 150369 Limestone Brachiopod (?)fragments Silurian(?) Pickett In hand specimen the rock is composed of breccia Crinoid ossicles 1971 angular fragments of limestone 10 to 30 mm in diameter, cemented by iron and lime carbonates with sand-size particles. The larger clasts are rather recrystallized though outlines of fragments of crinoid ossicles and probable brachiopod fragments can be distinguished. Captains Flat Formation IV o o East of Vanderbilt Hill at Captains Flat 217581 A fine green tuffaceous shale band Favosites cfgothLandicus Favosites Sp? Alveolites spp. Rugosa Crinoid stems Bryozoa Cf Lingula Rhynchonellid Silurian (~lenlock­ ian?) Glasson 1957 L. Sherwin (pers. comm.) suggests that the fauna are only indicative of a Silurian age in the broadest sense. APPENDIX 2 SELECTED PETROLOGICAL DESCRIPTIONS In the following descriptions the "T" number is the number of the thin section in the collection of the Geological and Mining Museum, Sydney. 1.DAHINABY BEDS 1. SiZtstone. metamorphosed (L.M. Barron 1974d, p. 1) GR 831213 T 26210 Grains of quartz (.15 mm, 10%) are set in a metamorphosed silty matrix of quartz + opaques + muscovi te flakes + minor biotite + rare tourmaline + apati te. The mica flakes define a strongly crenulated cleavage. FOXLOW BEDS 2. FeZdspathia greywaake. metamorphosed (L.M. Barron 1975a, p. 2) GR 197564 T 27854 Grains of angular An25 (0.15 mm, 5%) and subangular quartz (0.9mm, 40%) are set in a foliated matrix of granoblastic quartz (0.1 mm, 40%), chlorite (0.04 mm, 3%), muscovite (0.04 mm, 10%), alkali feldspar (0.04 mm, 1%) and limonite (0.01 mm, 1%). 3. Sandy siZtstone. silicified (L.M. Barron 1975b, p. 4) GR 152679 T 27889 Grains of quartz (0.4 mm, 35%) with sutured margins and overgrowths are set in 0.04 mm silty matrix of overgrown quartz + minor sericite + opaques. 4. Sandy muddy siZtstone. foliated, metamorphosed (L.M. Barron 1975a, p. 2) GR 168486 T 27860 Grains of subangular alkali feldspar (0.9 mm, 3%), subrounded quartz (2 mm, 10%) and rounded An20 (0.9 mm 1%) are set in a foliated matrix of 0.1 mm granoblastic quartz and aligned flakes of muscovite +biotite. The hand specimen has two foliations with the second one minor. 5. Cordierite - biotite homfeZs (J. Barron 1972, p. 1) GR 073475 T 22695 The rock is a fine grained hornfels containing abundant poikiloblastic cordierite. Inclusions in the latter are muscovite, biotite and a few opaque grains. Interstitially surrounding the cordierite poikiloblasts the assemblage developed includes biotite, muscovite and quartz. Biotite is significantly more abundant outside the cordierite poikiloblasts. The original rock type 111111111111 1111111111111111111111111 1111/ 11111 111111111 /111 0004942100 202 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET was probably a fine grained pelitic lithology. Metamorphic grade is probably hornblende hornfels facies. 6. Chert black, cross fractured (L.M. Barron 1974d, p. 2) GR 980453 T 26197 The rock is a dense black .3 rom mottled chert with a few recrystallised ?sponge spicules and opaque granules. The rock has been cross fractured and the fractures have been healed by silicification and chert recrystallisation. The rock has been lightly stained by limonite. RYRIE FORMATION 7. Quartzite (L.M. Barron 1974d, p. 1) GR 980286 T 26206 Subrounded grains of quartz (.15 rom, 95%) are tightly fitted together with sutured margins, along with minor feldspar, zircon and opaques. The rock contains a small amount of clay. There are a few well formed blades of muscovite which, due to their size and random orientation, may be detrital. The rock has a mild foliation caused by suturing preferentially in one direction. COLINTON VOLCANICS 8. Daaitia lithia arystal pumiae tuff. altered, chert(?) matrix (L.M. Barron 1975c, p. 2) GR 970206 T 26614 The hand specimen shows abundant 1 rom highly compacted pumice lenses and rounded equant rock fragments set in a highly structured matrix. In thin section the rock consists of rounded fragments of 0.25 rom porphyritic ?dacite (2 cms, 10%), flattened lenses of pumice (0.3 rom x 1 rom, 15%), fragments of partially resorbed quartz (1 rom, 10%), rounded feldspar fragments (0.5 rom, 20%) and bent books of biotite (0.5 rom, 3%) which are set in a fine matrix composed of ?ash and recrystallized ?chert. The whole rock has been strongly altered with muscovite + sericite replacing feldspar, chlorite + epidote + leucoxene + sphene replacing biotite, chlorite + quartz replacing pumice and chlorite+leucoxene replacing the matrix. A few outlines of aurved glass shards are present and in addition the matrix does not appear to be eutaxitic: the rock has a good compaction foliation but is not welded and is not a vitric tuff. The rock may have formed from a pyroclastic turbidite. 9. Fine ash tuff. mildly altered (L.M. Barron 1974f, p. 2) GR 936268 T 26922 Angular .06 ~~ grains of quartz (10%), plagioclase (5%) and alkali feldspar (5%) are set in a matrix of .008 rom sericite + chlorite + quartz + zircon + leucoxene. Subaligned flakes of muscovite (.1 rom, 4%) may be metamorphic. APPENDIX 2 The rock could be a fine-grained ash tuff or a silty mudstone with tuffaceous material. In some places there are highly angular .15 rom ?grains of .008 rom quartz + sericite which may be relict ash particles. The textures suggest the rock is a fine ash tuff but further work on field related rocks is needed. The composition, based on grain content, would have to be rhyodacitic. 203 10. SiZioeous ~hyoZitio Zithio ash tuff (L.M. Barron 1975c, p. 1) GR 969182 T 26610 The hand specimen shows a chalky cherty volcanic with a mild foliation defined by minor aligned phenocrysts and fragments. The rock is crisscrossed by conjugate quartz-healed fractures. In thin section the rock consists of subhedral partially - resorbed quartz (0.5 rom, 5\), wispy to blocky to cuspate bordered grains (1 rom, 5%) of 0.005 rom sericite + clay (pumice, feldspar, shards) and blocky Ti-magnetite (0.15 rom, 3\) which are set in a matrix rich in 0.005 rom sericite + clay and 0.04 rom rounded quartz ?recrystallization patches. 11. WeZded ~hyoZitio o~ystaZ tuff, altered (L.M. Barron 1974g, p. 1) GR 950492 T 26964 The hand specimen shows a mild alignment of phenocrystic fragments. In thin section angular fragments of subhedral partially resorbed quartz (1 rom, 10\), subhedral sanidine (0.5 rom, 15\), subhedral biotite (1 rom, 3\) and subhedral plagioclase (0.5 rom, 8\) are set in a moderately welded 0.15 rom blocky shard matrix which has been recrystallized to 0.005 rom quartz + leucoxene + sericite + chlorite with intershard cavities being filled with chert. The eutaxitic structure shows best in cross polarized light because of an enhanced differential recrystallization of flattened glass shards. Undeformed glass shards occur where crystal fragments have piled up so as to provide a halo of protection against flattening. Moderate alteration has resulted in strong replacement of plagioclase by sericite + biotite + epidote + leucoxene, and moderate replacement of biotite by leucoxene + epidote + clay. There is not any metamorphic foliation. WILLIAMSDALE VOLCANICS 12. Rhyodaoitio o~ystaZ Zithia tuff, altered (L.M. Barron 1975c, p. 4) GR 975625 T 26618 Angular fragments of 0.3 rom granitic aplite (3 cm, 5%), quartz (1 rom, 6\), plagioclase (0.5 rom, 5\), biotite (1 rom, 8\), magnetite (0.15 rom, 2\), alkali feldspar (0.5 rom, 10\), blocky ?glass blebs (1 rom, 4\) now altered to chlorite + epidote + leucoxene and single crystals of quartz (5 1IIIll, 5\) are set in a matrix now recrystallized to 0.004 rom quartz + chlorite + leucoxene + zircon + minor sericite. This matrix does not have any relict or metamorphic structure. The fragments are subaligned and give the rock a mild primary foliation. The rock has been moderately altered with abundant sericite + epidote replacing feldspar, chlorite + epidote + sphene replacing biotite, leucoxene replacing magnetite. 204 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET The crystal fragment textures and the grainsize of the matrix suggest the rock is a crystal lithic tuff of rhyodacitic composition. 13. Rhyodacitia lithia arystal tuff, altered (L.M. Barron 1974e, p. 1) GR 959521 T 27154 Elongated, hot moulded fragments (1 x 5 cm, 30%) of rhyodacite porphyry with subhedral quartz, An30, biotite and opaques in a matrix of .008 mm quartz + chlorite + leucoxene, fragments of biotite (1 mm, 10%), euhedral quartz (1 mm, 25%), plagioclase (.5 mm, 8%), sanidine (2%), and fragments of sulphides (2%) are set in a .008 mm matrix (25%) of quartz + chlorite + leucoxene + carbonate. The fragments are aligned. Feldspars are moderately altered to sericite + carbonate + chlorite, and biotite to chlorite + leucoxene + epidote. There is no evidence for a eutaxitic structure in the matrix so the rock may be a lithic tuff with a ash + subsequent chert matrix. 14. Miaroadamellite intrusive porphyry, altered (L.M. Barron 1975c, p. 5) GR 978603 T 26616 Subhedral sanidine (1 mm, 8%), subhedral quartz (1 mm, 10%), euliedral An28 (2 mm, 5%), and subhedral biotite (0.5 mm, 3%) are set in a 0.01 mm vermicular intergrowth of quartz + alkali feldspar. Moderate alteration has produced sericite in feldspar and matrix and chlorite + epidote + leucoxene in biotite. The textures support an intrusive origin. BRANSBY BEDS 15. Welded arystal tuff(?) or spherulitia rhyolite(?), recrystallized (L.N. Barron 1974a, p. 2) GR 922188 T 24485 Subhedral .5 mm crystals and fragments of alkali feldspar (10%), plagioclase (5%), quartz (10%), muscovite (5%) and rare ?pumice are set in a recrystallized matrix with relict ?ash and relict ??welded/flow texture. The matrix now consists of granoblastic quartz, sericite, feldspar and leucoxene. The rock could be a recrystallized welded ash crystal tuff or a recrystallized spherulitic lava. 16. Volaania arkosia greywaake(?) or arystal tuff (?), altered with epidote (L.M. Barron 1974a, p. 1) GR 913202 T 24482 Angular 1 mm fragments of quartz, alkali feldspar and An25 are set in a matrix of .1 mm angular quartz, alkali feldspar, plagioclase, opaques and fine-grained indistinct quartz-sericite-chlorite. The rock has been sheared, silicified and extensively altered with epidote while chlorite is common in the very fine-grained matrix. The angular texture suggests the rock is either a volcanic arkosic greywacke or a crystal tuff. Shearing has destroyed textures in the matrix which would differentiate between these two alternatives APPENDIX 2 205 but the high epidote content suggests the rock may have originally been limy. KOHINOOR VOLCANICS 17. Rhyodacitic crystal tuff, mildly altered (L.M. Barron 1975a, p. 1) GR 213558 T 27850 Angular fragments of An28 (0.4 mm, 2%), alkali feldspar (0.4 mm, 5%), and subrounded fragments of quartz (0.5 mm, 5%) are set in a mottled matrix of 0.01 mm quartz + feldspar + serici te + chlori te. Mild alteration has produced sericite in feldspar. 18. Rhyolite lava, tuffaceous (L.M. Barron 1975a, p. 1) GR 220556 T 27852 Euhedral An33 (2 mm, 5%), eU!1edral alkali feldspar (2 mm, 20%), polycrystallinesubhedralquartz(4 mm, 20%), vesicles (1 mm, 5%) filled with epidote + quartz and ?pumice fragments are set in a slightly metamorphically foliated matrix of quartz + sericite + epidote + feldspar + chlorite. 19. Porphyritic rhyolite, recrystallized, altered (L.M. Barron 1974c, p. 1) GR 131302 T 26212 Rounded, partially resorbed quartz (2 mm, 8%), and subhedral plates of ?biotite (1 mm, 3%) are set in a granoblastic .04 mm matrix of quartz and .1 mm limonite-stained patches of ?feldspar (20%). Most quartz phenocrysts are whole so the rock is probably a high silica acid volcanic that has been strongly recrystallized and altered. 20. Andesite, altered (L.M. Barron 1974c, p. 1) GR 120237 T 25268 Anhedral resorbed quartz (.5 mm, 4%), subhedral An35 (.5 mm, 10%) and strongly altered biotite (.2 mm, 5%) are set in a .02 mm microlitic and 0.1 mm granular matrix of An20 (20%), epidote (20%), sphene (8%), and chlorite (20%). The rock has been strongly altered especially in the matrix. Phenocrysts of plagioclase are replaced by epidote while biotite is strongly replaced by chlori te + epidote. 21. Andesite,altered (L.M. Barron 1974c, p. 1) GR 121167 T 26202 Euhedral augite (1.5 mm, 20%), vesicles (2%), subhedral An30 (1 mm, 15%) and subhedral biotite (1 mm, 8%), after hornblende are set in a 0.1 mm matrix of blades and granules of epidote, anhedral and microlitic plagioclase, chlorite, and opaques. The rock is moderately altered with vesicles being filled ~li.th chlorite +quartz, biotite altering to chlorite and plagioclase altering to epidote + sericite. 206 LIVINGSTONE PORPHYRY GEOLOGY OF THE MICHELAGO 1:100,000 SHEET 22. (L.M. Barron 1974c, p. 2) GR 941450 T 26194-1 This thin section contains three rock types with boundary relations: The boundary between I and II is defined best by a difference in matrix grainsize and is both fairly linear and sharp to gradational over 0.15 rom. The boundary between II and III is irregular, and is defined both by differences in matrix grainsize and sericite content. Furthermore III has an increase in fine angular semi-opaques (?leucoxene) at its margin. The boundary between III and I is well defined by matrix grain size and is sharp. Obvious truncation of phenocrysts by these contacts was not seen. I Intrusive daaitia porphyry, altered Anhedral resorbed quartz (1 rom, 12%), euhedral alkali feldspar (1 rom, 8%), euhedral plagioclase (1 rom, 13%), subhedral biotite (1 rom, 10%), and subhedral apati te (.3 rom, 2%) are set in a subgraphic .1 rom matrix of quartz + chlori te + opaques + plagioclase laths + alkali feldspar + epidote + leuxocene. The rock is moderately altered with epidote + chlorite + quartz +leuxocene after biotite, and sericite + epidote after feldspar. Some phenocrysts of both quartz and feldspar have .15 rom quartz graphic overgrowths. The matrix textures suggest the rock is intrusive. II Daaitia porphyry Subhedral resorbed quartz (1 rom, 10%), subhedral biotite (1 rom, 8%), anhedral opaques (.3 rom, 5%), subhedral An25 (.3 rom 5%), and subhedral alkali feldspar (.3 rom 5%) are set in a .02 rom matrix of quartz +plagioclase laths + zircon + leucoxene + chlorite + epidote + alkali feldspar. The phenocrysts preferentially altered with epidote + chlorite after biotite, muscovite + chlorite after feldspar and leucoxene after opaques. The textures in the matrix suggest the rock could be either intrusive or extrusive. III Aphanitia rhyodaaitia roak, altered, ? recrystallized One 0.5 rom rounded grain of 0.1 rom polycrystalline muscovite is set in a 0.03 rom polygonal matrix of quartz + plagioclase laths + muscovite + alkali feldspar + opaques + chlorite +leucoxene + epidote. There are several .1 rom thick irregular leucoxene-rich tracks which cross this rock type but stop at the contact to I and II. The plagioclase laths and muscovite flakes in the matrix suggest the rock could be a fine-grained intrusive rock, or else these features could have developed in a fine-grained rock by contact metamorphic recrystallization .. The thin section T26l94-2 also comes from specimen M57, and it contains rock I, although the phenocrysts are considerably larger (2-3X) in T26l94-2 than they are in T25l94-l. Conclusions (T26194) APPENDIX 2 207 Rock III has a different composition to I and II and in addition there are no phenocrysts in III while II and particularly I have numerous phenocrysts. Hence rock III is not contemporaneous with I and II and is probably a fragment caught up in II. The matrix differences between I and II support the suggestion that II could be an earlier phase of I, subsequently ripped from the wall and incorporated into I. BULLANAMANG PORPHYRY 23. Granite. subporphyritic, mildly altered (L.M. Barron 1974g, p. 3) GR 923239 T 26971 Anhedral poikilitic perthitic alkali feldspar (1.3 rom, 3S%), subhedral quartz (O.S- rom, 4S%), and subhedral An33 (0.3 rom, 20%) are packed together with thin veins of quartz cutting them. Mild alteration has produced sericite in plagioclase. The hand specimen shows the rock to be 80% of a 1 rom grainsize with 20\ irregular patches of a 2 - 10 rom grainsize. MICHELAGO IGNEOUS COMPLEX ~~NKELLAN GRANODIORITE 24. Biotite - hornbLende granodiorite. hybrid, mildly altered (L.M. Barron 1974g, p. 2) GR 003464 T 26967 The rock in hand specimen consists of S -10 rom clots of biotite + hornblende set in a 1 rom background of feldspar + quartz + biotite. In thin section the clots are composed of subhedral hornblende (0.2 rom, 4S%), anhedral quartz (0.2 rom, 30\), subhedral biotite (0.2 rom, 10%) and subhedral An27 (0.2 rom, lS%) which are all tightly fitted together. Mild alteration has produced minor epidote + sericite in plagioclase and epidote + actinolite in hornblende. The contact zone between the clot and the host rock is composed almost entirely of poikilitic quartz. The host rock consists of euhedral biotite (1 rom, 10%), no hornblende, anhedral poikilitic subgraphic quartz (1 rom, 40%), anhedral microcline (O.S nun, lS\), subhedral zoned plagioclase (An4S-An35' 1 nun, 30%) and anhedral opaques (0.2 r,un, 3%). Mild alteration has produced chlorite +.epidote + leucoxene in biotite, sericite + leucoxene + epidote + quartz in plagioclase. The host rock is a biotite granodiorite while the clots have a composition of a hornblende biotite quartz diorite. The textures suggest either the clots are a crystallization phenomena rather than digested xenoliths, or the whole rock is an almost completely digested xenolith with the digestion converting most of the rock to biotite granodiorite but leaving behind relict clots of hornblende quartz diorite. The second model is believed to be the better one due to the margin around the clots and the absence of hornblende in the host rock. Thus the rock is a hybrid biotite + hornblende granodiorite. 208 ONSLOW GRANODIORITE GEOLOGY OF THE MICHELAGO 1:100,000 SHEET 25. Granodiorite, mildly granulated and altered (L.M. Barron 1974b, p. 3) GR 017333 T 26192 Subhedral An45 (1 rom, 40%), anhedral polycrystalline quartz (2 mm, 25%), subhedral biotite (2 rom, 12%), subhedral hornblende (1 rom, 8%) and anhedral alkali feldspar (1 rom, 10%) are tightly fitted together with minor magnetite and rare zircon and apatite. The rock is mildly altered with epidote + calcite + sericite after plagioclase and epidote after biotite. The textures suggest mild granulation as the last phases were crystallising. MICALIGO ADAMELLITE 26. Biotite - hornblende adamellite, mildly altered (L.M. Barron 1974a, p. 1) GR 994405 T 24481 Subhedral 2 - 5 rom crystals of zoned, albite-mantled An25, biotite, and subordinate perthitic alkali feldspar are set in a subgraphic .4 rom matrix of quartz, biotite, perthitic alkali feldspar, plagioclase, hornblende and minor magnetite, muscovite. Plagioclase is altered with epidote-calcite-sericite. KOOLAMBAH ADAMELLITE 27. Adamellite, altered (L.M. Barron 1974g, p. 3) GR 031235 T 26974 Anhedral subperthitic microcline (1 rom, 20%), subhedral plagioclase (1 rom, 30%), subhedral quartz (1 rom, 30%), euhedral biotite (1 rom, 7%), subhedral hornblende (1 rom, 8%) and anhedral opaques (0.1 rom, l%) associated with biotite are fitted together with mild alteration producing abundant sericite + epidote + leucoxene in plagioclase, epidote + chlorite in biotite and epidote +actinolite in hornblende. 28. Adamellite, subporphyritic, mildly altered (L.M. Barron 1974g, p. 3) GR 024196 T 26973 Subhedral plagioclase (2 rom, 35%), subhedral to anhedral quartz (1 - 5 rom, 25%), subhedral biotite (1 rom, 5%), subhedral hornblende (1 rom, 10%), subhedral sphene (0.2 rom, 1%), subhedral perthitic alkali feldspar (1 rom, 25%) and anhedral opaques (0.1 rom, 5%) associated with hornblende are fitted together with rare apatite. Mild alteration has produced epidote + sericite in plagioclase and chlorite + epidote in biotite. MINOR PHASES IN THE SOUTHERN BoDY 29. Biotite granite, moderately altered (L.M. Barron 1974a, p. 3) GR 006251 T 24491 Minor anhedral 1 - 5 rom crystals of perthitic alkali feldspar and quartz APPENDIX 2 are set in a .3 Inm matrix of quartz, perthitic alkali feldspar, minor An20, biotite and rare opaque. The rock is moderately altered with sericite-epidote after feldspar. 209 30. Porphyritic granite. mildly weathered (L.M. Barron 1974a, p. 2) GR 099238 T 24488 Subhedral 1 - 2 rom crystals of quartz, perthitic alkali feldspar and minor An30 are set in a .05 rom matrix of subgraphic perthite-quartz and minor plagioclase. Minor sericite occurs after feldspar in both matrix and porphyries. Feldspars are mildly weathered with clay. 31. Greisen(?) dyke. with fragment of siltstone (L.M. Barron 1974b, p. 2) GR 051227 T 26205 The thin section shows two rock types. The finer grained rock appears to be in a rounded 1 x 5 cm fragment, although only 240 0 of the fragment boundary shows in the thin section. This fragment is composed of granoblastic .1 rom quartz (10%), muscovite (10%), biotite (5%) and feldspar (3%) with finer opaques, apatite, zircon, ?garnet and tourmaline. The mineralogy and textures suggest the rock was a siltstone, possibly with a mild tectonic foliation before it became incorporated in the second rock type. The second rock type consists of sUbangular grains of quartz (2 rom, 10%) and An25 (1 rom, 3%) which are set in a polygonal matrix of .15 rom quartz (30%), opaques (5%), muscovite/sericite (30%), biotite (10%) and plagioclase (5%), along with minor .015 rom grains of zircon, apatite and tourmaline. The mineralogy and textures suggest the rock may be a greisen or a granitised sandy shale. SAPLING FLAT IGNEOUS COMPLEX DANSWELL CREEK GRANODIORITE 32. Hornblende biotite adamellite (L.M. Barron 1974g, p. 4) GR 129348 T 26975 Subhedral hornblende (1 rom, 4%) with poikilitic inclusions of apatite and zircon, subhedral biotite (2 rom, 6%), subhedral An27 (1 rom, 40%), anhedral microcline (2 rom, 30%) with mild perthite, anhedral quartz (1 rom, 20%) and anhedral opaques (0.2 rom, 3%) associated with biotite or hornblende are fitted together with very mild alteration producing sericite + carbonate + chlorite + epidote in plagioclase. WANGRAH ADAMELLITE 33. Adamellite (L.M. Barron 1974b, p. 1) GR 110255 T 25276 Subhedral microcline (1 - 10 rom, 30%), anhedral quartz (1 - 3 rom, 25%), anhedral sphene (.5 rom, 5%), subhedral biotite (.5 rom, 8%), anhedral magnetite 210 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET (.2 mm, 5%) and subhedral zoned plagioclase (1 mm, AnZO-ZS I 20%) are fitted together with inclusions of muscovite, zircon, and apatite. The rock is mildly altered with calcite + sericite + epidote after plagioclase and chlorite after biotite. BREDBO RIVER ADAMELLITE 34. Adamellite, altered, mildly granulated (L.M. Barron 1974b, p. 2) GR 117166 T 25274 Subhedral microperthitic alkali feldspar (l - 20 mm, 30%), subhedral AnZ5 (2 mm, 20%), anhedral biotite (1 mm, 10%) and subhedral quartz (1 mm, 25%) are fitted together with inclusions of muscovite, apatite, magnetite and zircon. Deformation has resulted in a crenulated twinning in plagioclase, and undulatory extinction in quartz. Mild alteration has produced epidote + sericite + calcite in plagioclase and epidote + chlori te in biotite. 35. Adamellite, porphyritic (L.M. Barron 1974b, p. 2) GR 115160 T 26200 Porphyries of subhedral quartz (1 mm, 15%), subhedral zoned plagioclase (2 mm, An35-~O' 15%), and subhedral perthitic alkali feldspar (3 mm, 10%) are set in a polygonal .15 mm matrix of biotite (3%), quartz (20%), AnZ5 (10%), microcline (20%) and euhedral apatite (2%) and zircon (1%). Mild alteration has caused sericite + calcite in plagioclase and chlorite in biotite. XENOLITHS IN BREDBO RIVER ADAMELLITE 36. Granitized sediment (L.M. Barron 1974a, p. 5) GR 117167 T 24772 The rock consists of fine to coarse-grained granoblastic quartz, biotite, muscovite, alkali feldspar, An30 with minor apatite and opaque. The quartz content is exceptionally high and the rock could be a granitized sediment. Although biotite-muscovite is randomly oriented, there is a vague banding visible which may be relict bedding. TINDERRY GRANITE 37. Biotite granite, mildly altered (L.M. Barron 1974b, p. 1) GR 043421 T 24462 Subhedral An30 (1 mm, 15%), anhedral perthitic alkali feldspar (1 mm, 45%), anhedral quartz (.5 mm, 30%) and anhedral biotite (.5 mm, 5%) are tightly fitted together with rare zircon. The rock is mildly altered with epidote in plagioclase and biotite. APPENDIX 2 38. Adamellite porphyry, moderately altered (L.M. Barron 1974b, p. 1) GR 050423T 24463 211 Subhedral An25 (1 rom, 25%), subhedral quartz (.7 rom, 10%) and subhedral orthoclase (.3 rom, 5%) are set in a granoblastic .06 rom matrix of quartz, biotite, feldspar and sericite. The rock is moderately altered, especially in the matrix with epidote after feldspar while leucoxene is patchily distributed. The matrix has mild flow structuring. URIALLA GRANITE 39. Biotite granite, altered (L.M. Barron 1975d, p. 1) GR 048610T 26932 Subhedral microcline (2 rom, 40%), anhedral opaques (3%), anhedral quartz (1 rom, 25%), subhedral An20 (0.7 rom, 20%) and subhedral biotite (0.3 rom, 5%) are fitted together with a mild graphic structure between quartz and feldspar. Moderate alteration has produced abundant sericite + epidote in plagioclase and epidote + leucoxene + chlori te in biotite. The rock is not foliated and has a somewhat mottled concentration of biotite. 40. Gl'anodioritic po-rphyry, flow foliated, altered (L.M. Barron 1975d, p. 1) GR 044597T 26933 Euhedral An30 (1 rom, 5%), subhedral quartz (3 rom, 5%), biotite (0.5 rom, 3%) and opaques (0.1 rom, 3%) are set in a foliated matrix of anhedral feldspar microlites, sphene, abundant chlorite + epidote, quartz, and fine opaques. Strong al teration has produced sericite + prochlori te + epidote in feldspar, epidote in quartz, epidote in a few rare vesicles and epidote + quartz + leucoxene+chlorite in biotite. There may be a few relict outlines of completely altered ?pyroxene (or hornblende) phenocrysts (0.3 rom, 3%). The microlitic texture in the matrix supports a pre-alteration composition of granodioritic porphyry. 41. Intrusive(?) adamellite porphyry, altered (L.M. Barron 1974b, p. 4) GR 030617T 26199 Subhedral 1 - 5 rom porphyries of An35 (15%), resorbed quartz (15%), alkali feldspar (8%) and granular epidote completely replacing biotite (5%) are set in a granoblastic .025 rom matrix of quartz, biotite, plagioclase, epidote, alkali feldspar and chlorite. The phenocrysts of quartz have highly poikilitic overgrowths into the surrounding matrix. The rock is moderately altered with epidote + sericite in plagioclase. The textures suggest the rock could be a shallow intrusive. 212 WATCH BOX GRANITE GEOLOGY OF THE MICHELAGO 1:100,000 SHEET 42. Granite, mildly crushed, mildly altered (L.M. Barron 1974f, p. 2) GR 071597 T 26920 Anhedral quartz (3 mm, 35%), anhedral poikilitic microcline (3 mm, 30%), subhedral An30 (1 mm, 20%) and subhedral biotite (.4 mm, 8%) with minor inclusions of apatite and opaques are tightly fitted together with some granulation and pressure suturing of quartz and deformation of biotite. Mild alteration has produced sericite + granular clinozoisite in the cores of plagioclase, epidote + sphene in biotite and rare clinozoisite in cracks in alkali feldspar. 43. Muscovite microgranite, mildly crushed, mildly altered (L.M. Barron 1974f, p. 2) GR 087603 T 26921 Subradiating 1 mm patches of muscovite (.3 mm, 10%), subhedral An28 (.5 mm, 10%), anhedral quartz (.5 mm, 25%) and anhedral microcline (.5 mm, 20%) are set in a background of .07 mm similar mineralogy. The rock has been mildly crushed, producing strained extQnction and sutured margins in quartz, bent plagioclase and bent muscovite. Mild alteration has produced sericite in feldspar and rare epidote in fractures. The rock has a mild parallel ~ structure, due to the deformation features mentioned. MINOR ACID TO INTEFMEOIATE INTRUSIONS 44. Granitic intrusive porphyry (L.M. Barron 1974f, p. 1) GR 890666 T 26916 Euhedral subperthitic sanidine (2 mm, 10%), euhedral quartz (1 - 2 mm, 10%) , euhedral An30 (1 mm, 4%) and anhedral muscovite (.1 mm, 2%) are set in a .009 mm matrix of quartz + feldspar + muscovite + minor granular epidote and leucoxene. Feldspars are moderately stained with limonite as is the matrix. Neither the matrix nor the phenocrysts show a flow alignment. The textures suggest the rock is either an intrusive porphyry or a lava. The field relations suggest the rock may be an intrusive. 45. AdameZlite porphyry (L.M. Barron 1975b, p. 4) GR 138576 T 27890 Subhedral An33 (0.6 mm, 20%) anhedral elongate quartz (0.7 mm, 10%) and subhedral perthitic alkali feldspar (0.6 mm, 20%) are set in a matrix of An30 (0.2 mm, 10%), alkali feldspar (0.1 mm, 2%), muscovite (0.5 mm, 2%), biotite (0.03 mm, 3%) and quartz (0.1 mm, 40%). Mild alteration has produced minor epidote + seric"ite in feldspar and the matrix. 46. Microgranodioritic porphyry dyke, highly foliated (L.M. Barron 1974g, p. 2) GR 133572 T 26969 Ellipsoids (1 x 3 mm, 10%) of 0.1 mm polygonal quartz, subhedral An25 (1 mm, 5%), with poikilitic inclusions of 0.03 mm quartz and 0.5 x 2 mm trails APPENDIX 2 of 0.03 rom biotite (5%) and/or 0.03 rom muscovite (2%) are set in a strongly foliated matrix of 0.05 rom quartz + feldspar + minor biotite + minor muscovite + sphene + epidote + zircon. The foliation wraps about the phenocrysts in augen structure. The textures suggest the rock is most likely an intrusive dyke that has Leen elongated by tectonism. 213 47. Gran-Zte porphyry dyke, foliated, metamorphosed (L.M. Barron 1975b, p. 3) GR 176457 T 27883 Rounded crystals of plagioclase (0.5 rom, 15%), quartz (0.5 rom, 2%) and perthitic alkali feldspar (1 rom, 25%) are set in a subgneissic layered matrix of foliated 0.05 rom quartz + epidote + carbonate + biotite. The metamorphic foliation wraps around the phenocrysts producing an augen structure. 48. Granitic subporphyry dyke, strongly foliated (L.M. Barron 1975b, p. 1) GR 174490 T 27870 Angular crystals of quartz (0.9 rom, 3%) with polycrystalline margins, and rounded grains (0.9 rom, 6%) of subhedral An31 + muscovite + quartz + alkali feldspar are set in a foliated matrix (0.008 rom, 90%) of oriented quartz + biotite + muscovite + granular epidote. The metamorphic foliation wraps around phenocrysts. JERANGLE IGNEOUS COMPLEX 49. Contact: metagreywacke to aZtered granite (L.M. Barron 1974b, p. 4) GR 135145 T 25285 The thin section shows two rock types with a sharp contact between the two. The first rock type consists of subangular grains of quartz (.5 rom, 20%) and angular grains of sericite + quartz + biotite (.2 rom, 20%) which are set in a .004 rom matrix of sericite, chlorite, quartz and opaques. In the matrix, subradiating .5 rom flakes of honey-coloured biotite (5%) have grown. This rock was possibly a lithic greywacke. The second rock type consists of subhedral partially resorbed phenocrysts of quartz (1 - 4rom, 30%) and subhedral blades of muscovite (1 rom, 8%) and biotite (.3 rom, 3%) which are set in a .01 mm matrix of sericite + quartz + clay + carbonate with irregular patches of altered opaques. A vague 1 rom texture in the matrix suggests that ?feldspars have been completely altered. The textures suggest that the rock was a subporphyritic granitic rock. ANEMBO GRANODIORITE 50. Granodiorite, altered (L.M. Barron 1974b, p. 1) GR 167163 T 25281 Euhedral zoned plagioclase (2 - 3 rom, 25%, An3S-An25), anhedral quartz (1 - 7 rom, 30%), subhedral hornblende (l rom, 5%), euhedral biotite (.2 - 3 rom, 10%) and microcline (1.3 rom, 10%) are fitted together with inclusions of magnetite, apatite, zircon. Hornblende is pale brown to green, pleochroic. There is a single .06 rom crystal of ?garnet with an inclusion of zircon. Alteration is 214 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET moderate and has produced epidote + sericite + tremolite in plagioclase, chlorite + epidote + clinozoisite +calcite in biotite, clinozoisite in microcline and rimming chlorite + epidote after hornblende. XENOLITH IN ANEMBO GRANODIORITE 51. Hornblende - biotite adamellite, altered (L.M. Barron 1975c, p. 7) GR 188335 T 26957 Subhedral hornblende (1 rom, 25%) with poikilitic inclusions of opaques, apatite and rare relict cores of au~ite, subhedral biotite (1 rom, 5%) with inclusions of opaques and subhedral An32-3G (0.5 rom - 1 rom, 25%) are set in a subophitic background of anhedral orthoclase (1 rom, 20%) and quartz (1 rom, 15%) . Moderate alteration has produced chlorite + epidote + leucoxene in biotite and leucoxene + epidote + sericite in feldspar. The rock is not foliated. TOWNEYS CREEK ADAMELLITE 52. Biotite adamellite, altered (L.M. Barron 1974b, p. 2) GR 164321 T 25283 Subhedral quartz (1 rom, 30%), subhedral microperthitic microcline (1 rom, 30%), subhedral An2S (1 rom, 20%) and subhedral biotite (.7 rom, 8%) are fitted together with inclusions of zircon, magnetite, apatite and muscovite. Moderate alteration has produced epidote + sericite +calcite in plagioclase, and quartz + chlorite + epidote in biotite, while mild weathering has produced a stained clay in the alkali feldspar. CAINOZOIC BASIC PLUG 53. Olivine teschenite, altered (L.M. Barron 1974a, p. 4) GR 123268 T 24766 Subhedral poikilitic F07S (2 rom, 8%), glomeroporphyritic 2 rom patches of augite (.2 rom, 5%) and round vesicles (.5 rom, 5%) filled with calcite, brownish zeolite and euhedral cubes of ?fluorite (.1 rom, 1%) are set in a subaligned matrix of FOGO (0.1 rom, 8%), Ansa (.1 rom, 35%), anhedral analcite (10%), subhedral magnetite (5%), calcite (2%) and augite (20%). Fine needles of apatite (2%) cut plagioclase in the matrix. Analcite is in intercrystalline patches and is usually fresh, so it was the last phase to crystallize, along with a rare amount of alkali feldspar. Olivine is altered with iddingsite. APPENDIX 3 MODAL ANALYSES, CHEMICAL ANALYSES, AND C.I.P.W. NORMS OF SELECTED ROCKS FROM THE MICHELAGO 1:100,000 SHEET AREA Clear Range Granodiorite Murrumbucka Tonalite Callemondah Granodiorite Shannons Flat Adamellite Tharwa Adamellite Murrumbidgee Batholith Leucogranites Monkellan Granodiorite Onslow Granodiorite Micaligo Adamellite Koolambah Adamellite A porphyry dyke in the Michelago Igneous Complex Danswell Creek Granodiorite Wangrah Adamellite Tinderry Granite Urialla Granite Anembo Granodiorite Towneys Creek Adamellite Boro Granite Quartz diorites in the Canberra Synclinorium Colinton Volcanics and Bransby Beds Intrusion(?) in Williamsdale Volcanics Chemical analyses of selected limestones (Carne and Jones 1919) 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 11111111111111111111111111111111 11111 11111 111111111111111111 D004942110 216 S.G. n.d. tr A.N.U. GEOLOGY OF THE MICHELAGO 1:100,000 SHEET ABBREVIATIONS specific gravity not determined trace this sign has been used as in original references Australian National University Abbreviations used in descriptions of modaZ composition Q quartz Kf K-feldspar Pl plagioclase Bi biotite Mu muscovite Hb hornblende Op opaques G groundmass A accessories N.B. Numbers are expressed as a percentage Abbreviations used in tabZes of C.I.P.W. nO:ffll Q quartz or orthoclase ab albite an anorthite C corundum di diopside wo wollastonite en enstatite fs ferrosi1ite hy hypersthene mt magnetite hm haematite il ilmenite ru rutile ap apatite cc calcite N.B. Numbers are expressed as a percentage APPENDIX 3 CLEAR RANGE GRANODIORITE 217 Total No. of counts Q Kf (microcline) Pl Bi Mu Hb Op G A S.G. 1 MODAL ANALYSIS ? 33.9 8.9 34.2 16.1 1.8 n.d 2.73 2 3 4 SiOz TiOZ AIZ 0 3 FeZ03 FeO MnO MgO CaO NaZO KzO PZOS HZO+ HZO- COZ Total Q or ab an C wo fs en mt il ap CHEMICAL ANALYSES 68.63 0.65 14.70 0.60 3.55 0.06 1. 90 2.93 2.21 3.40 0.08 loll 0.05 0.07 99.94 C. 1. P.W. NORMS 30.65 20.65 20.05 14.00 2.77 4.36 5.50 0.69 1.04 0.29 68.44 0.68 13.86 0.67 3.79 0.05 2.30 2.62 2.36 3.61 0.Z3 1.15 0.07 0.03 99.86 29.10 21.85 21.85 11.60 2.24 4.48 6.54 0.69 1.04 0.61 67.50 0.60 14.55 0.83 3.94 0.08 2.51 3.50 2.05 3.10 0.16 98.82 30.34 18.32 17.34 16.31 1. 84 di !!l. 11. 95 1. 20 1.14 0.37 1. Average of 7 microsections. (Snelling 1960, p. 193). 2. Fitzs Hill, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). 3. 1.6 km south of Flinders Trig. Station southwest of Bredbo, north of Cooma, N.S.W. Analyst Rudowski and Unwin (Joplin 1963). 4. Average of 16 analyses. Analyst A.S. Joyce (Joyce 1973a) . 218 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET MURRUMBUCKA TONALITE 49.07 45.53 0.69 1. 59 21. 76 17.82 3.44 4.76 8.74 8.17 0.00 0.15 3.65 5.44 10.32 10.95 1. 03 0.63 0.37 1. 83 tr 0.25 0.62 2.24 0.14 0.21 0.02 99.83 99.59 Total No. of counts Q Kf (microc1ine) PI Bi Mu Hb Op G A S.G. SiOz TiOZ A1Z0 3 FeZ 0 3 FeO MnO MgO CaO NaZO KZO PZOS HZO+ HZO- COZ Total Q or ab 1 2 3 MODAL ANALYSIS ? 39.9 nil 40.6 18.7 nil 0.8 2.74 CHEMICAL ANALYSES 63.67 50.76 0.69 0.80 14.81 23.10 1.04 1.66 4.73 5.27 0.07 0.08 3.70 3.in 5.13 5.85 1. 94 3.63 2.69 3.64 0.15 0.10 1. 38 1.48 0.08 0.09 0.03 0.03 100.11 99.50 C.I.P.W. HORMS 22.06 16.65 17.80 24.37 0.34 5.86 10.56 1.03 1.04 0.29 4 8.63 2.19 8.71 51.18 0.091 5 1. Average of 4 microsections (Snelling 1960, p. 193). 2. Xenolith. 10.4 km south-southeast of Murrumbucka Trig. Station, north of Cooma, N.S.W. Analyst Rudowski and Unwin (Joplin 1963). 3. Bredbo, near Cooma, N.S.W. Analyst Rudowski and Unwin (Joplin 1963). 4. Xenolith. Murrumbucka, near Cooma, N.S.W. Analyst G.A. Joplin (Jop1i~ 1963). 5. Xenolith. Murrumbucka, near Cooma, N.S.W. Analyst Rudowski and Unwin (Joplin 1963). Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H20+ H20- C02 Total Q or ab an C wo fs en mt il ap APPENDIX 3 219 CALLEI10NDAH GRANODIORITE 1 2 CHEMICAL ANALYSES 69.21 67.88 0.66 0.62 13.46 14.54 0.99 0.74 3.77 3.94 0.09 0.07 1.93 2.32 2.35 3.13 1. 94 2.25 3.35 2.52 0.17 0.15 1.46 0.06 0.07 99.51 98.16 C.I.P.W. NORMS 34.11 32.81 20.95 14.89 18.05 19.03 11.50 14.54 2.97 2.78 4.42 5.58 !:X. 11. 50 1.05 1.07 1.04 1.18 0.32 0.35 1. "Boboyan" homestead, northwest of Cooma, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). 2. Average of 6 analyses. Analyst A.S. Joyce (Joyce 1973a). 220 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET SHANNONS FLAT ADAMELLITE 1 2 3 4 5 6 Total No. of counts Q Kf (microc1ine) PI Bi Mu Hb Op G A S.G. MODAL ANALYSIS ? 36.0 21.0 34.7 8.3 n.d. n.d. 2.66 CHEMICAL ANALYSES Si02 Ti0 2 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H2 0+ H2 0- C02 Total Q or ab an C wo fs en mt il ap 73.. 02 0.38 12.49 0.60 1. 64 0.05 1. 21 2.45 2.75 4.40 0.12 0.65 0.05 0.07 99.88 C. 1. P. W. NORMS 31.12 26.70 25.55 8.82 1. 30 1.62 3.40 0.67 0.56 0.26 72.5 0.30 13.7 0.44 2.50 0.02 0.51 2.45 2.20 3.90 0.07 1.19 G.07 99.85 37.26 23.04 18.61 11. 69 1. 58 ~ 5.04 0.64 0.57 0.16 70.31 0.35 18.68 0.63 1.83 1.10 2.22 1. 37 3.32 0.06 0.65 0.09 100.61 42.39 19.62 11. 59 10.62 8.49 ~ 5.00 0.91 0.66 0.14 74.23 0.32 12.60 0.50 1. 34 0.06 0.31 2.80 2.98 3.72 0.08 0.75 0.06 0.03 99.78 35.05 22.25 27.40 10.57 1.18 1.42 0.92 0.51 0.46 0.24 72.21 0.36 13.90 0.59 1. 90 0.05 0.85 2.43 2.64 4.31 0.09 99.33 33.02 25.46 22.33 11. 46 0.69 ~ 4.61 0.86 0.68 0.21 1. Average of 19 microsections (Snelling 1960, p. 193). 2. Alum Creek, 5 km northwest of Shannons Flat, near Cooma, N.S.W. Analyst Rudowski and Unwin (Joplin 1963). 3. Northwest of Tharwa, A.C.T. Analyst J.C. Watts (Joplin 1963). 4. Shannons Flat, west - northwest of Cooma, N.S.W. Analyst G.A. Joplin (Joplin 1963). 5. Northwest of Tharwa, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). 6. Average of 25 analyses. Analyst A.S. Joyce (Joyce 1973a). APPENDIX 3 THARWA ADAMELLITE 221 1 2 3 4 5 6 n.d. 2.69 2.68 2.69 CHEMICAL ANALYSES 72.74 71. 56 0.43 0.46 13.16 13.92 0.89 0.77 1. 83 2.12 0.02 0.02 0.80 0.60 2.55 2.61 2.56 2.84 4.14 4.32 0.15 0.15 0.70 0.79 0.06 0.04 0.05 0.05 Total No. of counts Q Kf (microcline) PI 8i Mu Hb Op G A S.G. Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H2 0+ H2 0- C02 Other constituents Total MODAL ANALYSIS ? 34.1 29.7 29.1 7.1 n.d. 100.08 C. I.P. W. NORMS 100.25 2.698 75.14 72.11 73.01 0.21 tr 0.34 12.42 13.89 13.65 0.61 1. 28 0.56 0.68 2.00 1. 90 0.02 tr 0.04 0.57 1. 30 0.83 1. 55 4.47* 2.24 3.18 2.66* 2.74 4.74 0.16* 4.04 0.09 0.05 0.10 0.54 1.12 0.05 0.12 0.03 0.43 C1 = tr Li20 = tr 99.83 99.59 99.45 Q or ab an C wo fs en mt il ap 32.91 25.10 23.95 12.25 0.02 1.60 2.28 1.02 0.58 0.29 30.13 32.68 34.72 26.20 28.30 23.87 25.65 29.45 23.17 12.20 5.67 10.46 0.24 0.94 0.66 1.82 0.36 di 1. 70 1. 58 ~ 4.60 0.85 0.67 0.81 0.92 0.34 0.65 0.29 0.29 0.23 * 1. 2. 3. 4. 5. 6. Alkalis or CaO transposed. Average of 8 microsections, S.G. average of 2 specimens (Snelling 1960, p. 193). Tharwa quarry, Tharwa, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). West side of Castle Hill, Tharwa, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). Granite porphyry, Tharwa village, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). Tharwa, A.C.T. Analyst A.G. Hall (Joplin 1963). Average of 5 analyses. Analyst A.S. Joyce (Joyce 1973a). 222 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET MURRUMBIDGEE BATHOLITH LEUCOGRANITES Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H2 0+ H20- C02 Total Q or ab an C wo fs en mt il ap 1 CHEMICAL ANALYSES 76.95 0.09 12.82 0.22 0.57 0.05 0.12 0.67 3.07 5.24 0.05 99.85 C. I.P.W. NORMS 37.22 30.96 25.97 3.00 1.00 ~ 1.11 0.32 0.17 0.12 2 75.66 0.25 12.72 0.60 0.64 0.01 0.23 0.82 2.90 4.89 0.06 0.63 0.06 99.47 36.26 29.70 26.85 3.55 1. 56 0.22 0.68 0.69 0.34 0.15 1. Average of 4 analyses. Analyst A.S. Joyce (Joyce 1973a). 2. Aphyric microgranite. 5 km northwest of "Booroomba" homestead, A.C.T. Analyst Rudowski and Unwin (Joplin 1963). APPENDIX 3 MONKELLAN GRANODIORITE 1 CHEMICAL ANALYSIS SiOZ 65.79 TiOZ 0.48 A1Z0 3 13.92 FeZ03 1. 29 FeO 3.46 MnO 0.08 MgO 3.58 CaO 4.13 NaZO 2.98 KZO Z.62 PZOS 0.10 HZO+ 1.46 HZO- 0.08 COZ 0.05 Total 100.02 C.I.P.W. NORM Q 23.34 or 15.98 ab 25.55 an 16.96 C 0.00 di 2.33 wo 0.00 hy 12.50 rot 1.96 il 0.92 ap 0.24 cc 0.12 1. GR 003464. Analyst The Australian Mineral Development Laboratories (AMDEL 1977). 223 224 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET ONSLOW GRANODIORITE 1 CHEMICAL ANALYSIS SiOz TiOZ A1Z03 FeZ03 FeO MnO MgO CaO NaZO KZO PZOS HZO+ HZO- COZ Total 65.49 0.49 14.17 0.80 3.96 0.09 3.48 4.66 Z.96 2.63 0.09 0.89 0.07 0.03 99.81 C.I.P.W. NORM Q 21.79 or 15.99 ab 25.28 an 17.64 C 0.00 di 4.06 wo 0.00 hy 12.67 mt 1.25 il 0.94 ap 0.22 cc 0.07 1. GR 025319. The Australian Mineral Development Laboratories (AMDEL 1977). APPENDIX 3 MICALIGO ADAMELLITE 1 CHEMICAL ANALYSIS 225 SiOZ TiOZ Alz03 FeZ03 FeO MnO MgO CaO NazO KzO PzOs HzO+ HZO- COz Total 72.60 0.33 13.35 0.95 1.64 0.05 0.97 2.84 2.65 3.30 0.06 0.48 0.06 0.03 99.31 C • 1. P •W. NORM Q 36.63 or 20.08 ab 22.66 an 13.71 C 0.39 di 0.00 wo 0.00 hy 4.21 mt 1.43 il 0.63 ap 0.14 cc 0.07 1. GR 994405. Analyst The Australian Mineral Development Laboratories (AMDEL 1977). 226 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET KOOLAMBAH ADAMELLITE Total No. of counts Q Kf Pl Bi Hb Op G A Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H20+ H2 0- C02 Total Q or ab an C di wo hy mt il ap 1 MODAL ANALYSIS 3412 35.9 13.5 38.6 6.1 5.2 0.8 CHEMICAL ANALYSES 70.30 0.45 14.01 1. 58 2.17 0.08 1.10 3.94 2.56 2.94 0.10 1.09 0.04 0.00 100.36 C. I. P. W. NORMS 33.59 17.37 21.66 18.05 0.00 0.69 0.00 4.47 2.29 0.85 0.23 2 68.88 0.43 14.25 1. 34 2.42 0.05 1.61 4.20 2.67 2.69 0.07 0.95 0.07 0.03 99.66 31.15 16.46 22.85 19.00 0.00 1. 23 0.00 6.17 2.03 0.83 0.17 1. GR 012216. Analyst N.R.P. Baczynski (Baczynski 1970). 2. GR 024199. Analyst The Australian Mineral Development Laboratories (AMDEL 1977). APPENDIX 3 PORPHYRY DYKE IN MICHELAGO IGNEOUS COMPLEX 1 MODAL ANALYSIS 227 Total No. of counts Q Kf Pl Bi Hb Op G A SiOZ TiOZ A1Z0 3 FeZ 0 3 FeO MnO MgO CaO NaZO K2 0 P20S HZO+ HZO- C02 Total Q or ab an C di wo hy rot il ap 4257 7.7 2.7(?) 17.7 10.2 61.8 n.d. CHEMICAL ANALYSIS 69.01 0.47 14.68 0.62 1. 50 0.04 1.17 5.00 4.92 0.24 0.10 1. 07 0.08 0.63 99.53 C.I.P.W. NORM 28.08 1.42 41.63 17.26 5.59 1. 74 0.90 0.89 0.23 1. GR 015190. Analyst N.R.P. Baczynski (Baczynski 1970). 228 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET DANSWELL CREEK GRANODIORITE 1 MODAL ANALYSES 2 3 4 Total No. of counts Q Kf PI Bi Hb Op G A Over 4000 30.3 23.0 36.0 8.9 1.4 0.26 Traces of apatite alld zircon 29.4 29.3 28.7 9.3 3.0 0.3 Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H2 0+ H2 0- C02 CHEMICAL ANALYSES 72.20 0.52 13.44 0.67 3.63 0.10 0.68 2.17 3.29 3.89 0.17 71. 67 0.53 13.21 0.64 3.24 0.09 0.61 1. 83 3.27 4.02 0.14 0.42 0.04 0.03 Total Q or ab an C di wo hy mt il ap 100.76 C. 1. P.W. NORMS 30.11 22.99 27.84 10.42 0.00 0.30 0.00 6.98 0.97 0.99 0.37 99.74 30.66 24.24 27.80 8.05 0.48 0.00 0.00 6.26 0.94 1. 01 0.33 1. 2. 3. 4. Average of Xenoliths. GR 120335. GR 129348. 5 analyses (Richards 1967). GR 124334 (Richards 1967). Analyst D.N. Richards (Richards 1967). Analyst The Australian Mineral Development Laboratories (AMDEL 1977). Total No. of counts Q Kf Pl Bi Mu Op Si02 Ti02 Ali 0 3 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H2 0+ H20- C02 Other constituents Total Q or ab an C di wo hy mt il ap cc APPENDIX 3 229 WANGRAH ADAMELLITE 1 2 3 4 5 MODAL ANALYSIS Over 4000 32.8 34.6 28.5 3.6 0.05 0.4 CHEMICAL ANALYSES 73.09 75.60 77.10 76.90 0.17 0.45 0.07 0.12 13.89 12.60 12.37 12.67 0.59 0.25 0.65 0.33 1.15 1. 52 0.53 1. 25 0.05 0.03 0.02 0.03 0.20 0.14 0.11 0.25 1. 23 0.97 0.71 0.79 3.33 3.20 3.81 3.05 5.61 4.95 5.03 4.89 0.12 0.06 0.03 0.09 0.56 0.35 0.02 0.03 n.d. 0.03 V203 = tr Cr203=tr CuO tr BaO = 0.07 100.08 100.18 100.43 100.37 C.I.P.W. NORMS 29.02 35.16 34.25 37.75 33.14 29.25 29.73 28.90 28.16 27.06 32.24 25.81 5.32 4.23 1.80 3.39 0.39 0.43 1.12 1. 26 0.01 1. 93 2.25 2.50 0.86 0.36 0.94 0.48 0.32 0.85 0.13 0.23 0.28 0.14 0.07 0.20 0.07 I L 1. Average of 5 analyses (Richards 1967). 2. 3 km west of Jerangle, N.S.W. Analyst J.H. Pyle (Joplin 1963). 3. ANU age date material No. GA 311 (unpubl.). 4. Analyst D.N. Richards (Richards 1967). 5. Analyst D.N. Richards (Richards 1967). 230 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET TINDERRY GRANITE 1 CHEMICAL ANALYSIS SiOz TiOZ Alz03 Fez03 FeO MnO MgO CaO NazO K20 P20S H2 0+ H20- C02 Total Q or ab an C di hy mt il ap C. 1. P • W• NORM 77 .2 0.08 12.4 0.34 0.80 0.03 0.09 0.48 3.65 4.35 0.02 0.34 0.07 99.85 37.73 25.70 30.87 2.25 0.87 1. 34 0.49 0.15 0.05 1. Tinderry Range, Michelago, N.S.W. Analyst J.C. watts (Joplin 1963). APPENDIX 3 URIALLA GRAN ITE 1 CHEMICAL ANALYSIS 231 Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H20+ H2 0- C02 Total 69.49 0.36 14.56 0.99 2.03 0.03 2.05 3.04 2.70 2.57 0.06 1. 53 0.03 0.03 99.47 C.!. P. W. NORM Q 34.05 or 15.73 ab 23.28 an 14.83 C 2.00 di 0.00 wo 0.00 hy 7.57 mt 1. 50 il 0.70 ap 0.15 cc 0.07 1. GR 043606. Analyst The Australian Mineral Development Laboratories (AMDEL 1977). 232 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET ANEMBO GRANOOIORITE Total No. of counts Q Kf Pl Bi Hb op G A 1 Over 4000 32.7 19.4 39.9 6.3 1.5 0.3 2 18.9 8.7 48.5 13.3 9.6 0.8 3 MODAL ANALYSES CHEMICAL ANALYSES 4 5 6 7 Si02 66.03 68.68 71.10 67.83 61.21 Ti02 0.52 0.46 0.07 0.51 0.72 A1203 14.53 15.66 13.80 14.26 14.65 Fe203 1. 74 1.16 0.86 1. 01 1. 53 FeO 3.38 2.90 2.63 3.39 5.48 MnO 0.09 0.08 0.05 0.09 0.18 MgO 1. 91 1.49 0.97 1. 69 3.41 CaO 4.56 4.19 3.30 4.41 6.07 Na20 2.78 2.88 2.90 2.62 2.96 K2 0 2.82 2.89 3.30 2.83 2.29 P20S 0.18 0.13 0.08 0.07 0.13 H20+ 1. 08 0.69 0.80 H20- 0.26 0.09 0.04 CO2 0.07 0.04 0.03 Other constituents V203 = tr SrO=n.d. BaO=0.05 Total 100.00 100.52 99.88 99.58 98.63 C.I.P.W. NORMS Q 25.78 28.29 31. 72 28.62 15.88 or 16.66 17.08 19.50 17.22 13.53 ab 23.51 24.37 24.53 22.41 25.05 an 18.84 20.02 14.90 18.85 19.93 C 0.00 0.46 0.00 0.00 di 1.77 0.00 0.59 2.21 7.78 wo 0.00 0.00 0.00 0.00 0.00 hy 7.96 7.47 6.21 7.88 12.59 mt 2.52 1. 68 1. 25 1. 54 2.22 il 0.99 0.87 0.13 0.98 1. 37 ap 0.42 0.28 0.19 0.17 0.28 cc 0.16 0.00 0.09 0.07 0.00 1. Average of 5 analyses, swift point counter setting 1/3 x 1/2 rom interval (Richards 1967) . 2. xenolith. Average of 3 analyses (Richards 1967) . 3. 6.4 kID east-northeast of Jerangle, N.S.W. Analyst J.H. Pyle (Joplin 1963). 4. GR 167277. Analyst D.N. Richards (Richards 1967). 5. ANU age date material No. GA 310 (unpub1.) . 6. GR 189335. Analyst The Australian Mineral Development Laboratories (AMDEL 1977). 7. Xenolith. Analyst D.N. Richards (Richards 1967) . APPENDIX 3 TDWNEYS CREEK ADAMELLITE 233 Total No. of counts Q Kf PI Bi Hb Op Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 KZO PZOS HZO+ HZO- C02 Total 1 MODAL ANALYSIS Over 4000 32.7 34.3 29.1 3.3 0.5 0.01 CHEMICAL ANALYSIS C. I. P . W. NORM 2 75.08 0.18 13.85 0.56 1.13 0.05 0.51 2.00 2.87 4.58 0.09 100.90 Q 35.40 or 27.07 ab 24.29 an 9.39 C 0.73 di wo hy 2.68 mt 0.81 i1 0.34 ap 0.20 1. Average of 3 analyses (Richards 1967). 2. Analyst D.N. Richards (Richards 1967). 234 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET BORO GRAN ITE 1 CHEMICAL ANALYSIS Si02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K20 P20S H2o+ H2O- C02 Total Q or ab an C di wo hy rot il ap 73.70 0.30 12.60 0.94 1.81 0.04 0.71 2.65 2.75 3.65 0.06 0.87 0.11 100.19 C.I.P.W. NORM 36.54 21. 56 23.26 11. 26 1. 24 3.27 1. 36 0.57 0.14 1. Boro, east of Lake George, N.S.W. Analyst J.C. Watts (Joplin 1963). APPENDIX 3 QUARTZ DIORITES IN THE CANBERRA SYNCLINORIUM 235 S.G. Si02 Ti02 A1203 Fe20 FeO MnO MgO CaO Na20 K2 0 P20S H20+ H2 0- C02 Total Q or ab an C di hy mt il ap 1 2.75 CHEMICAL ANALYSES 63.35 0.84 16.92 1. 23 4.58 3.03 4.45 1.90 2.28 tr 0.86 0.09 99.53 C.I.P.W. NORMS 26.80 13.47 16.07 22.07 3.24 13.55 1. 78 1.60 2 64.43 0.10 18.61 1. 52 2.14 2.13 5.20 2.47 1.87 0.11 1.06 0.26 99.90 27.77 11.05 20.89 25.07 3.34 7.81 2.20 0.19 0.25 1. Murrumbucka, near Cooma; Portion 46, Parish York, County Beresford. Analyst G.A. Joplin (Joplin 1943). 2. Quartz -mica diorite. North of Cooma, N.S.W. Analysts E.A. Burnard and E.T. Wallace (Joplin 1943). 236 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET COLINTON VOLCANICS AND BRANSBY BEDS Total No. of counts Q Kf PI Bi Mu Hb Op & (epidote) G A Chlorite laths Calcite Choritized S.G. SiOZ TiOz Alz0 3 FeZ 0 3 FeO MnO MgO CaO NazO KZO PZOS HZO+ HZO- COz Other constituents Total Q or ab 1 2 3 MODAL ANALYSES 2357 ? 22.5 20.2 3.7 ( 28.4 (29.2 6.6 0.2 1.5 n.d. 35.4 42.5 0.2 n.d. 4.5 n.d. 3.6 n.d. n.d. 1.5 2.66 CHEMICAL ANALYSES 69.13 66.16 75.66 0.39 0.59 0.20 13.67 14.06 14.42 0.52 1.58 1.21 1.89 3.01 0.11 0.06 1.64 0.47 0.59 2.70 2.66 0.09 3.86 4.05 1. 34 3.57 1.67 4.74 0.10 0.12 0.11 1. 53 2.12 1. 91 0.05 0.10 2.05 1. 34 4 2.731 67.33 0.65 14.03 1.86 2.88 0.03 2.47 2.72 4.36 1.71 0.22 1. 76 0.10 0.03 BaO = 0.04 SnO = tr (NiCo) 0 = tr 100.19 24.75 10.10 26.88 13.37 0.11 8.88 2.70 1. 23 1. Colinton Volcanics. GR 945205. Analyst N.R.P. Baczynski (Baczynski 1970). 2. Colinton Volcanics. GR 979201. Analyst N.R.P. Baczynski (Baczynski 1970). 3. Rhyolite (slightly sheared). Analyst G.A. Joplin (Joplin 1943). 4. 3 km north of Cooma, N.S.W. Analyst J.C.H. Mingaye (A. Rep. Dep. Mines N.S.W. for 1908, p. 184). APPENDIX 3 INTRUSION(?) IN WILLIAMSDALE VOLCANICS 1 CHEMICAL ANALYSIS 237 5i02 Ti02 A1203 Fe203 FeO MnO MgO CaO Na20 K2 0 P20S H20+ H20- C02 Total 70.65 0.53 13.54 1.17 2.62 0.07 1.46 3.20 2.31 3.21 0.11 0.52 0.08 0.03 99.50 C.I.P.W. NORM Q 35.28 or 19.18 ab 19.75 an 15.13 C 0.79 di 0.00 wo 0.00 hy 6.81 mt 1.72 il 1. 02 ap 0.26 cc 0.07 1. GR 009644. Analyst The Australian Mineral Development Laboratories (AMDEL 1977). CHEMICAL ANALYSES OF SELECTED LIMESTONES (Carne and Jones 1919) Assay County Parish Grid Locality Formation CaC03 MgC03 MnC03 Fe203 P20S Gangue Organic H2 O Total No. reference , , , and , , Matter , A1203 ,, 210 Beresford Abercrombie 994149 Portion 13, 140 m Cappanana 95.50 4.04 0.02 0.32 - 0.36 - - 100.24 east of Bredno Formation River. 211 Beresford Bransby 924239 Portion 184, 7.25 Ian Bransby 97.67 0.69 0.03 0.18 - 1.26 - - 99.38 north-northeast of Beds Bredno. 212 Beresford Bransby 922252 Portion 90, 7.65 Ian Bransby 97.28 0.63 0.05 0.26 - 1.98 - - 100.20 north-northeast Beds of Bredbo. 213 Beresford Bransby 978144 Portion 82, west Cappanana 97.14 tr 0.02 0.32 - 2.54 - - 100.02 of Bredbo River, Formation 8.05 Ian east of Bredno. 214 Beresford Bransby 972209 Portion 5, 7.25 Ian Cappanana 96.68 tr 0.06 0.32 - 2.82 tr - 99.88 north-northeast Formation of Bredno. 215 Beresford Bransby 972209 Portion 5,7.25 Ian Cappanana 88.75 1.55 - 1.60 - 8.10 - - 100.00 north-northeast Formation . of Bredbo. 216 Beresford Bransby 923263 Portion 89, near Colinton 99.14 tr 0.02 0.16 - 0.70 - - 100.02 Gungoandra Creek Volcanics and Murrumbidgee River, 8.05 Ian north-northwest of Bredbo. 223 Beresford Gungoandra 976231 ML 17, 8.05 Ian Cappanana 98.37 0.45 0.04 0.22 - 1.12 tr - 100.20 northeast of Formation Bredbo. 224 Beresford Gungoandra 971241 Portion 34, 8.05 Ian Cappanana 96.80 1.87 0.06 0.20 - 1.24 tr - 100.17 northeast of Formation Bredbo. '"w CD I-' I-' o o o o o lJl :x: t'l t'l 0,3 226 Beresford Micaligo 930420 Southwest corner of Bransby 97.78 0.30 0.02 0.34 - 1.62 - - 100.06 Portion 122, 7.25 kID Beds southwest of Miche1ago on Murrumbidgee River. 227 Beresford Micaligo 932448 South end of Bransby 99.12 0.56 0.02 0.08 - 0.46 - - 100.24 Portion 213, east Beds bank of Murrumbidgee River, 3.22 kID west of Michelago. 228 Beresford Micaligo 932451 Portion 213, near Bransby 96.83 0.66 0.10 0.34 - 2.30 - - 100.23 junction of Beds limes tone and porphyry, 3.22 kID west of Michelago. 457 Murray Ballallaba 213625 40 m east of Copper 94.66 4.07 0.02 0.20 - 1.28 tr - 100.23 Bungendore - Captains Creek Flat road, 4.83 kID Shale from Captains Flat. 458 Murray Ballallaba 215672 Portion 104, Copper 99.00 - - 0.06 - 0.86 - - 99.92 north of Captains Creek Flat. Shale 461 Murray Surra 050674 London Bridge, Cappanana 94.59 2.42 0.04 0.72 - 2.10 0.13 100.00 20.93 kID south- Formation southeast of QUeanbeyan. 482 Murray Jinjera 180458 Portion 1, 12.08 kID Copper 97.58 1. 33 0.01 0.42 - 0.56 - - 99.90 south of Captains Creek Flat. Shale 487 Murray Monkellan 003527 Portion 29, close Colinton 93.21 2.86 0.08 0.80 - 2.94 tr - 99.89 to Miche1ago - Volcanics Burra road, 9.66 kID north-northeast of Miche1ago. 488 Murray Monkellan 934496 East bank Bransby 95.71 tr 0.10 0.34 - 3.80 - - 99.95 Murrumbidgee 8eds River near northwest corner of Portion 156, 564 kID north- west of Miche1ago. ~ ." ." M Z o H :< Assay County Parish Grid Locality Formation CaC03 MgC0 3 l1nC03 Fe203 P20S Gangue Organic H2O Total No. Reference % % % and % % Matter % A1203 % % 489 Murray Monkellan 933483 Southwest corner of Bransby 97.21 tr 0.12 0.30 - 2.40 - - 100.03 Portion 79, 4.03 kIn Beds W 20 o N. of Michelago. 490 Murray Monkellan 929520 Hanging Rock, Bransby 96.17 1.07 0.10 0.38 - 2.38 tr - 100.10 Murrumbidgee Beds River, CPL 248, 11.27 kIn north- west of Michelago. 500 Murray Urialla 049666 Portion 15, Cappanana 97.14 2.25 0.02 0.24 - 0.70 - - 100.35 approximately 24 kIn Formation from Michelago. 501 Murray Urialla 043658 Portion 120,24.15 kIn Cappanana 95.62 2.16 tr 0.38 - 2.04 tr - 100.20 north-northeast of Formation Michelago. 502 Murray Urialla 017612 Portion 4, near Cappanana 98.32 0.46 0.04 0.28 - 0.66 - - 99.76 Michelago - Burra Formation road, 19.32 kIn from Michelago. APPENDIX 4 AGE DETERMINATIONS The following age determinations have been carried out on units which crop out in the area of the Michelago 1:100,000 geological sheet. Those ages to which a map number has been assigned are derived from samples originating from the Michelago sheet area. In the case of the unnumbered dates, the locations of the samples are either on neighbouring sheets, are on the Michelago sheet but with their exact location unknown, or the ages are derived from the average of several samples. COllUllents are made regarding the accuracy of the results as in many cases the derived age is too young. All the ages were calculated using the following decay constants: K/Ar age dating 40 AK 6 4.72 x 10- 10 yr- 1 40 KA e Rb/Sr age dating Rb/Sr 1.39 x 10- 11 yr- 1 If the values are recalculated using new constants and new spike calibrations, the K/Ar values generally indicate a greater age and the Rb/Sr age becomes younger. 1/111/11/11111111111111/1/1/1111 III/I 1/11///1/1 //1// 11///11/ 0004942120 Map NO. Grid reference Unit Age (m.y.) Method Reference Remarks 1 3 874681 870653 875623 From Tantangara and Brindabella 1: 100,000 sheets Tharwa 348 Adamellite Tharwa 376 Adamellite Tharwa 423 ± 6 Adamellite Shannons Flat Adamellite - northern area 423 ± 2 - southern area 419 ± 2 K-Ar K-Ar Rb-Sr Rb-Sr Rb-Sr Evernden and Richards 1962 Evernden and Richards 1962 Roddick and Compston 1976 Roddick and Compston 1976 Roddick and Compston 1976 GAISl, Australian National University catalogue number. G5, Canberra 1:250,000 Geological Sheet (Best et al. 1964). This sample was collected within half a kilometre of the Murrumbidgee Fault. Undulose extinction of quartz and evidence of crushing throughout the rock can be seen when the sample is examined under the microscope. It would appear that some argon has been lost from the biotite at the time of straining and crushing associated with movement on the Murrumbidgee Fault. Therefore, the K-Ar age derived from the biotite in the sample is considered useless. GA154, Australian National University catalogue number. G4, Canberra 1:250,000 Geological Sheet (Best et al. 1964). This specimen was collected close to a major fault on the eastern margin of the Murrumbidgee Batholith~ The strain effects shown by certain minerals indicate that the rock has partly recrystallized under this shearing stress. Some argon has been lost as a result and therefore the derived K-Ar age is suspect and must be ignored. The biotite was analysed. GA20528, Australian National University catalogue number. An age of 412 ± 4 was derived by Rb-Sr analysis of mica within a sample of the Tharwa Adamellite. The mineral isochron for the same sample is 416 ± 8 m.y. so the younger biotite age is possibly caused by a fault zone near the sample location. Therefore, rejection of the biotite from the isochron appears to be valid. Regression of plagioclase - mic·rocline - total rock only results in an age of 423 ± 6 m.y. Roddick and Compston (1976) compared on the basis of Joyce's (1973b) subdivision of the Shannons Flat Adamellite into two (comagmatic) phases, a northern and a southern phase. Some 17 samples for the northern area and 19 samples for the southern area were analysed for total rock and minerals. The small difference between the two groups is due to a difference in mineral ages and dominantly in biotite ages. The conclusion is reached that either the two phases were intruded at slightly different times or the southern phase has been affected thermally, thus delaying the final time of cooling to the 300·C blocking temperature of biotite. 4 814533 Clear Range 419 ± 4 Rb-Sr Roddick and GA20535, Australian National University catalogue number. Granodiorite Compston 1976 The biotite was analysed. The results are considered by Roddick and Compston (1976) to be fairly accurate. 5 814533 Clear Range 418 ± 4 Rb-Sr Roddick and GA20576, Australian National University catalogue number. Granodiorite Compston 1976 This xenolith sample was collected from the same locality as sample No. 4. Biotite was analysed by Rb-Sr methods and the results were similar to that of No. 4. Location unknown Booroomba 424 ± 2 Rb-Sr Roddick and This value was calculated from a group of samples. The isochron but most likely Leucogranite Compston 1976 for the Booroomba Leucogranite shows wide dispersion in Rb-Sr on Michelago and results in an age of 424 ± 2 m.y. The very close agreement 1:100,000 sheet both in age and initial ratio with the northern phase of the Shannons Flat Adamellite implies that the leucogranite was derived from the same source as the adamellite and that differentiation from the same magma is probable. From Tantangara Callemondah 419 ± 4 Rb-Sr Roddick and GA20546, Australian National University catalogue number. 1:100,000 sheet Granodiorite Compston 1976 A single biotite age determination has been made on the Callemondah Granodiorite at this locality. 6 049424 Tinderry 37B K-Ar Evernden and GA192, Australian National University catalogue number. Granite Richards 1962 G3, Canberra 1:250,000 Geological Sheet (Best et al. 1964) • The granite is a massive high-level intrusion unaffected by regional metamorphism or strong later movement. J.R. Richards (pers. comm.) now considers that this age is too young. A biotite sample was analysed. 7 015326 Onslow 395 ± 8 K-Ar Rowley 1975 A biotite sample was analysed by K-Ar methods to give a result Granodiorite (unpubl. ) of 395 ± B m.y. similar to that calculated for the Tinderry Granite. This age may be a little young as the petrology shows the specimen to have suffered some granulation in its last phase of crystallization. Another possibility is that the effect of adjacent minor faults has led to some loss of argon. 8 129348 Danswell 356 ± 7 K-Ar Rowley 1975 Biotite (356 ± 7 m.y.) and hornblende (353 ± 7 m.y.) weraanalysed. Creek 353 ± 7 K-Ar (unpubl.) The mineral pair gave virtually ideptical ages but the date is Granodiorite significantly younger than that of ne1ghbouring granites. Some granulation of the sample, due to adjacent faulting (the Narongo Fault), was responsible for updating the K-Ar ages. Location unknown Sapling Flat 325 ± 10 K-Ar Richards 1967 GA311 , Australian National University catalogue number. but definitely Igneous Complex (unpubl. ) The number is unrealistically low and probably reflects the on Michelaao (Wangrah proximity of the Narongo Fault. A biotite sample was analysed. 1:100,000 s'heet Adamellite) Map Grid Unit Age Method Reference Remarks No. reference (rn.y.) 9 144278 Towneys Creek 393 ± 12 K-Ar Richards 1967 GA3l0, Australian National University catalogue number. Adamellite (unpubl.) . G7, Canberra 1:250,000 Geological Sheet (Best et al. 1964) . The age is similar to that obtained for the Boro Granite and Onslow Granodiorite. J.R. Richards (pers. comm.) recalculated the age to 396 rn.y. using the new K-Ar constants. From Araluen Boro Granite 390 K-Ar Evernden and GA188 , Australian National University catalogue number. 1:100,000 Richards 1962 G6, Canberra 1:250,000 Geological Sheet (Best et al. 1964) • sheet The granite intrudes Ordovician metasediments on the western side. The rock was probably subjected to some later movement but it is believed that this has had little effect on the granite mass. A biotite sample was analysed. I NDE X Items are listed alphabetically, except for counties, fossils, metallic deposits, non-metallic deposits, and parishes which have been gr~uped.together under the respective heading. The suffix "t" indicates that the ~tem ~s on a table, "f" that it is on a figure-, and "p" that it is on a photo. Acton 4t Adaminaby 21, 22 Adaminaby Beds 13, 16, 21-22, 25t, 79, 129, 136, 137, 147, 201 Adaminaby Military 1-mi1e sheet 22 Adjenbil1y Creek 115, 119 Alum Creek 220 Anembo 56, 57, 59, 116, 117, 200 Anembo Fault 115, 117, 118, 142 Anembo gossans 97, 153 "Anembo Granite" 114 Anembo Granodiorite 23t, 73, 74t, 114, 115, 116-117, 118, 125, 213-214, 232 Angle Crossing 83, 144 Apollo Road 82 Ara1uen 1:100,000 sheet 10, 115, 120, 244 Australian Mineral Development Laboratories (AMDEL) 223, 224, 225, 226, 228, 230, 232, 237 Australian National University 7, 30, 79, 242, 243, 244 Ba1dwins dacitic facies 60, 61 Ba11a11aba andesitic facies 60-61 Ba11a11aba Creek 60, 67, 127 Ba11a11aba Fault 30, 145 Ba11inafad Creek 178 barite 63, 151, 153, 154 base metal deposits 151, 153 Bathurst 1:250,000 Geological Sheet 98 "Bedlam Beds" 30 Bedlam Springs Creek 30 Bega Batholith 17, 21, 29, 71, 72, 73, 74t, 114, 119, 141, 151 Bega 1:250,000 Geological sheet 80 Benambran Orogeny 136, 138, 139, 146, 148, 149 Benambran - Quidongan Tectonic Stage 147 - 149, 150 Berrida1e Batholith 72 Berrida1e 1:100,000 sheet 21, 124 "Beverley Beds" 26 Binjura Beds 26 Black Mountain Sandstone 130, 149 Blue Bull Peak 114, 116 "Boboyan" 219 Bo1airo Granodiorite 77, 78 Bold Slate Range Fault 115, 142 Bollard prospect 153 Bomba1a 1 "Booroomba" 84, 222 Booroomba Leucogranite 17, 25t, 74t, 77, 83, 84, 243 Boro 119, 234 Boro Granite 17, 23t, 29, 73, 74t, 98, 108, 119-120, 127, 142, 142p, 153, 234, 244 Bowning Orogeny 10, 99, 109, 116, 136, 139, 143, 146, 148, 151 Bowning Tectonic Stage 147, 150-151 Braidwood 4t, 64, 120, 148 Braidwood Granite 153 Braidwood 1:100,000 Geological sheet 7, 119 Bransby Beds 1St, 16, 18t-19t, 24t, 42, 44, 45, 48-55, SOp-SIp, 52p, 54p, 88, 113, 126, 131, 138, 143, 144, 150, 155, 198-200, 204-205, 236, 238, 239, 240 Bredbo 4t, 5, 10, 13, 16, 21,31,33, 34, 35, 36, 38, 39, 41, 44, 48, 49, 53, 54, 55, 79, 80, 87, 88, 90, 90p, 97, 123, 125, 130, 131, 138, 139p, 143, 149, 149p, 153, 154, 155, 179, 180, 187, 188, 197, 217, 218, 238 "Bredbo" 186, 187, 196 Bredbo River 10, 13, 16, 27, 28, 33, 35, 55, 59, 63, 88, 89, 103, 104, 115, 119, 154, 178, 179, 195, 238 Bredbo River Adamellite 17, 23t, 74t, 103-105, 210 Brindabe11a 1:100,000 sheet 75, 84, 242 Bu11anamang Porphyry 16, 24t, 55, 86-88, 207 "Bu11ongong Shale Member" 26, 27 "Bumba1ong" 49 "Bundarra" 96 Bungendore 1, 55, 59, 64, 65, 239 Bunyan 38 Bureau of Mineral Resources Australia 7 Burra 28, 35, 45, 46, 47, 109, Ill, 113, 130, 131, 155, 198, 239, 240 Burra Creek 36, 37p, 185, 195 Burra Fault 30, 47, 137-138, 143 "Burra Limestone" 195 \\11\\\1 111\ 1111\ 1111\ 1\111 1111\ 11111 \\11\ \\11I 111\\ 11\\ 111\ D004942130 246 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Burra Trig. Station 47 Burrinjuck Dam 143 Caddigat Creek 124 Calabash Creek 126 "Ca11emondah" 81 Ca11emondah Granodiorite 17, 21, 25t, 74t, 77, 78, 81, 219, 243 Canberra 1, 4t, 75, 143, 148, 149, 150, 151, 154, 155, 198, 200 Canberra 1:50,000 Geological Sheet 7 Canberra 1:100,000 sheet 43, 45, 55, 57, 58, 59, 64, 65, 67, 68, 121, 149, 155 Canberra 1:250,000 Geological sheet 7, 38, 80, 108, 114, 153, 242, 243, 244 Canberra Plains 10 Canberra Synclinorium 13, 16, 17, 30, 33-55, 133, 138, 143-144, 145, 235 Canberra - Yass Rise 149, 150, 151 Cape Everard 114 "Cappanama Beds" 33 "Cappanamma Beds" 33 "Cappanana Beds" 33 Cappanana Creek 30, 33, 34, 179, 183, 184, 187, 189, 190, 191, 192, 196 Cappanana Formation 1St, 16,18t-19t, 24t, 30, 32, 33-36, 36p, 37p, 44, 45, 54, 91, 112, 130, 143, 150, 185-195, 238, 239, 240 "Cappawidgee" 28, 33, 34, 35, 178 Captains Flat 1, 3, 4, 4t, 6, 10, 13, 16, 17, 26, 27, 28, 29, 56, 57, 59, 60, 63, 64, 65, 66, 67, 98, 105, 107, 108, 116, 118, 119, 120, 121, 127, 131, 137, 139, 142, 144, 145, 147, 150, 151, 153, 154, 155, 178, 200, 239 "Captains Flat Beds" 55, 65 Captains Flat Formation 1St, 16, 19t, 25t, 55, 63, 64, 65-69, 132, 145, 150, 200 Captains Flat - Goulburn Synclinorial Zone 13, 133, 137, 144-145, 153 "Captains Flat Group" 55 Captains Flat Railway Station 56, 178, 200 Captains Flat Road 155 Captains Flat Synclinorium 13, 17, 27, 30, 55-69, 127, 130, 133, 137, 144-145, 155 Captains Flat Trough 150 Captains Flat type orebody 153 "Carwoo1a" 154 "Carwoo1a Beds" 57, 64 Carwoo1a Formation 1St, 16, 19t, 25t, 55, 64-65, 68, 131 Carwoo1a Trig. Station 64, 65 "Casey's" track 188 Castle Hill 221 Clear Range 76, 78 Clear Range Granodiorite 17, 21, 25t, 49, SOp-SIp, 74t, 76, 77, 78-79, 80, 84, 137, 217, 243 Cockatoo Creek 93, 95 Co1inton 1, 16, 38, 41, 44, 55, 85, 136, 153 Co1inton Gorge 196 Co1inton Hill 31, 32, 90, 130, 181, 182, 184 Co1inton Railway Station 39 Co1inton Trig. Station 28, 30, 31, 91, 124, 184 Co1inton Volcanics 1St, 16, 18t-19t, 24t, 35, 38-45, 40f, 42p, 47, 48, 53, 54, 55, 86, 91, 112, 126, 131, 137, 143, 144p, 196-198, 202-203, 236, 238, 239 ",Collingwood" 86, 91, 92p, 95, 193, 195 Collingwood Fault 30, 33, 86, 89, 91, 92p, 138, 145 Co1yers Creek 180, 192, 195 Connellys Gap 196 Coo1ringdon Beds 26, 48, 178 Cooma 1, 6, 11, 26, 33, 38, 75, 80, 143, 145, 151, 152, 154, 155, 178, 217, 218, 219, 220, 235, 236 Cooma 1:100,000 sheet 79, 80, 124 Copper Creek 56 "Copper Creek Beds" 55, 56 Copper Creek Shale 13, 1St, 16, 19t, 25t, 55, 56-59, 63, 131, 145, 150, 200, 239 Cosgrove Hill 1 Cosgrove Porphyry 16, 24t, 88 Cosgrove Trig. Station 88 Cotter Anticlinorium 13, 16, 75-85, 129, 133, 136-137 Cotter Dam 75 Cotter Fault 76 Cotter Horst 7, 10 Cotters crossing 49, 197, 198 County Beresford 48, 86, 93, 124, 192, 235, 238, 239 Murray 92, 178, 200, 239, 240 Cowra Trough 149, 150 INDEX Cowra - Yass Synclinorial Zone 13, 16, 133, 143-144, 153 Crimmins shearing shed 179 Cu11arin Anticlinorium 13, 17, 2i, 26, 30-32, 89-113, 129, 133, 136, 137-141, 142 Dam shaft 153 Danswell Creek 100 Danswell Creek Granodiorite 23t, 73, 74t, 98, 100-101, 102, 103, 209, 228, 243 Dicranograptu8 cZingani Zone 178 Duntroon 38 "Eastern Massive Fragmenta1s" 60 Electrolytic Zinc Co. of A/asia Ltd 60 E11iots Shale Member 62 Fitzs Hill 217 Flinders Trig. Station 217 fossils AcanthohaZysite8 sp. 193 Actinocera8 sp. 192, 195 ActinoptereZZa formo8a 187 Aegiria sp. 194 AZveoZite8 sp. 196, 200 AmpZexograptu8 sp. 182 Angopora cf hi8ingeri 186 Athyrisinidae sp. indet. 193 Atrypa sp. 190, 191, 192 Atrypa cf reticuZari8 197 Atrypina sp. 191 Atl'ypoidea sp. 186, 187, 196 Atrypoidea aU8traZi8 187, 196 bivalves 188, 189, 190 brachiopods 16, 24t-25t, 34, 66, 131, 151, 186, 187, 188, 189, 191, 192, 194, 197, 200 Brachyprion cf bendeniensi8 187 bryozoa 200 CaZymene sp. 192, 195 CZavofabeZZa sp. 196 CZimacograptu8 sp. 179, 180, 181, 183, 185 CZimacograptu8 bicorni8 178, 179, 180, 181, 183 CZimacograptus sp. cf C. bicorni8 178 CZimacograptus bicorni8 Zongi8pinu8 181 247 fossils (cont.) CZimaCOgraptu8 bicorni8 peZtifer 180 CZimaCOgraptu8 cf brevi8 178 CZimacOgraptu8 caudatu8 178, 181, 183 CZimacograptus exiguU8 182 CZimacograptus sp. cf C. minimu8 178 CZimacograptu8 mi88iZi8 181 CZimacograptu8 tubuZifel'U8 182 CZimacograptu8 cf tubuZifel'U8 182 coe1ospirid sp. indet. 191 corals 16, 34, 190, 193, 194, 199 Corynoides sp. 183 crinoids 25t, 34, 57, 66, 69, 185, 186, 188, 189, 190, 191, 192, 193, 194, 195, 196, 197, 198, 199, 200 CryptOgraptu8 sp. 182 Cryptograptus tricorni8 178, 179, 181, 183 CyathophyUum shear8byi 194, 195 CyathophyUum cf 8hear8byi 192, 195 CY8tiphyUum 199 "Cy8tiphyUum" sp. 196 Davidsoniacea sp. indet. 191 DiceZZograptu8 sp. 178, 179, 180 DiceZZograptu8 affini8 182 DiceZZograptus caduceus 181 DiceUograptus cf caduceus 182 DiceZZograptus Canp'lanatu8 ornatus 180 DiceUograptu8 sp. cf Comp'lanatu8 ornatu8 182 DiceZZograptus cf forchammeri 182 DiceZZograptu8 forchammeri fZexuo8u8 181, 183 DiceUograptus cf ornatus minor 179, 180 Dicranograptu8 sp. 178, 182 Dicranograptus cf brevicauZis 179 Dicranograptu8 cZingani 178 Dicranograptu8 hians 178, 180, 181, 182 Dicranograptu8 ? nichoZ8oni 180 Dicranograptu8 sp. cf D. ram08U8 180 Dicranograptu8 sp. cf D. ramOSU8 ZongicauZis 181, 182 Dicranograptu8 ram08U8 8pirifer 181 diplograptid fragments 180 DipZograptU8 sp. 178, 179 DisphyUum 200 248 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET fossils (cont.) HOWeZZeZU2 nuauZa 190, 191 HOWeZZeZU2 cf nuaUU2 192 fossils (cont.) Enarinurus sp. 186, 187, 188, 189, 190, 191, 192, 195, 196 Enarinurus sp. indet. 186 Enarinurus cf etheridgei 197 Enarinurus mitaheZZi 186, 187, 188, 189, 190 Enarinurus sp. cf E. mitaheZZi 187, 188, 190, 191, 192, 197 Enarinurus cf tuberauZosa 192 eospiriferid brachiopod 188 Eospiriferidae sp. indet. 189 Fardenia sp. 191 Favosites sp. 186, 187, 188, 189, 190, 191, 195, 196, 197, 198, 199, 200 Favosites aZZani 196 Favosites cf Angopora hisingeri 186 Favosites goldfussi 192, 195 Favosites gothZandiaus 192, 194, 195 Favosites cf gothU2ndiaus 200 FenesteZZa sp. 186 FenesteZU2 sp. indet. 186 fish bones 53 FistuZipora sp. 197 Gastropoda indet. 193 gastropods 191, 192 GU2ss0graptus sp. 183 GZyptograptus sp. 185 GZyptograptus inaertus 185 GZyptograptus cf serTatus 179 Goniophora sp. 193 graptolites 13, 22, 25t, 27, 30, 32, 129, 130, 178, 179, 180, 182, 183, 184 Hallidae 194 HaZysites sp. 187, 188, 190, 193 HaZysites austraZis 192, 195 HaZysites cf ahiZZagoensis 186 HaZysites Zithostrotionoides 186, 195 HeZioZites sp. 186, 187, 188, 189, 190, 191, 199, 200 HeZioZites daintreei 185, 186, 195 HeZioZites minuta 192, 195 Hemitrypa sp. 197 HeraophyZZum shearsbyi 185, 186, 196, 200 Homoeospira sp. 198 HoweZZeZU2 sp. 187, 188, 189, 190, 193, 194, 196, 198 HoweZZeZU2 angustipZiaata 197 Isorthis sp. 196 Kirkidium sp. 196 lamel1ibranchs 13, 183 Leptaena sp. 187 Leptodorrrus sp. 187 Leptograptidae sp. ineet. 183 Leptograptus sp. 178, 180 Leptostrophia sp. 198 LinguU2 sp. 193, 200 LinguU2 sp. s. 1. 200 LinguZeZU2 53 MaaropZeura sp. 189, 197 M~lletidae? sp. indet. 193 Mesograptus muZtidens 178 Mesograptus aff. muZtidens 178 Mesograptus cf muZtidens 178, 179 MesophoZidostrophia sp. 188, 189 MesophoZidostrophia nitens 197 MoZongia sp. 187 Monograptus sp. 183, 184, 185 Monograptus cf barTandei 183 Monograptus aommunis aorrmunis 185 Monograptus dubius 184 Monograptus e:x:iguus 184, 185 Monograptus gregarius 185 Monograptus cf intermedius 184 Monograptus Zobiferus 185 Monograptus cf marTi 184 Monograptus cf nodifer 184 Monograptus priodon 184 Monograptus sp. cf M. priodon 185 Monograptus reguZaris 184 Monograptus cf reguU2ris 184 Monograptus runainatus 185 MuaophyZZum arateroides 196 MuZtisoZenia tortuosa 195 Nemagraptus pertenuis 178 Nemagraptus triaornis 178 Neurograptus fibratus 181 NiakZesopora sp. 197 NuauZana sp. 193 Onyaopyge Ziversidgei 189 orthid brachiopod 197 Orthograptus sp. 180, 181, 182, 183, 185 INDEX fossils (cont.) Orthograptus spp. (= ?apiaulatus) 182 Orthograptus aaZaaratus 181, 182 Orthograptus aaZaaratus aautus 178, 181 Orthograptus aaZaaratus basiZiaus 182 Orthograptus foZiaaeus 182 Orthograptus pageanus spinosus 181 Orthograptus quadrimuaronatus 179 Orthograptus sp. cf O. quadrimuaronatus 183 Orthograptus trunaatus 183 Orthonota sp. 186 Orthonota sp. austraZis 186 Pachyporinae 193 Pantanaerus sp. 188 Paraayalas sp. 187, 193 pelecypods 188 pentamerid brachiopods 187, 188, 189, 191, 200 Pentamerinae 194 Pentamerus sp. 192, 196 Pentamerus sp. indet. 186 PetaZograptus sp. 185 Phacopid pygidium 187 Phacopinae, gen. et sp. indet. 197 Phaulaatis sp. 187, 189, 190, 191, 194 PhoZidostrophia (Mesopho ZidostrophiaJ sp. 190 PZasmopora sp. 199 po1yzoans 193 Praeotenodonta viotoriae 193 Produatus sp. 188 Psi Zophy ton 53 PyanostyZus ? sp. nov. 186, 195 Pyanosty.Zus cf Tryplasma prinaeps 185 Rastrites sp. 18? Retiograptus yassensis 180 Retio1itidae sp. indet. 183 rhynchone11id brachiopod 200 Rugosa 200 rugose corals 189, 190, 191, 196, 197, 199, 200 scutellids 191 SauteZZum sp. s 1. 196 Spinatrypa sp. 193 spiriferid brachiopod 188, 191 SpirineZZa sp. 187 Sponge spicules 129, 202 SpongophyZZum sp. 199 Stenopora sp. 190 249 fossils (cont.) Streptelasma sp. 189, 191, 192 Stromatopora sp. 192, 195 Stromatoporoid sp. indet. 192 stromatoporoids 187, 188, 195, 199 stropheodontid sp. 188 stropheodontid sp. indet. 193 Stropheodontidae indet. 189 strophomenid sp. 189, 190 Strophomenid sp. indet. 187, 190 syntrophiacea 189 Syringopora sp. 186, 187 Syringopora sp. indet. 186 Tryp1asma sp. 186, 187, 191, 193, 194, 199, 200 Tryplasma ZonsdaZei 192, 195 TrypZasma ZonsdaZei var. saalariformis 185, 186 Tryplasma vermiformis 192, 195 Tryplasma cf vermiformis 194, 195 worm tubes 67 "Fox1ow" 26, 64, 65, 154 Fox1ow Beds 13, 1St, 21, 25t, 26-30, 32, 35, 37p, 44, 55, 58, 59, 90p, 91, 106p, 129, 137, 138, 139p, 140, 141, 142, 142p, 143, 146, 147, 148, 149p, lSI, 178-183, 201-202 Fox1ow Creek 26 Fox1ow Trig. Station 26 Fyshwick 151-152 garnet 28, 209, 213 Giger1ine Trig. Station 113 G1adefie1d Volcanics 38 Golf Course Fault 145 "Good Good" 112, 126 Good Good Adamellite 17, 23t, 74t, 112 Googong 1 "Goosoon Beds" 48 Goosoon Creek 48 Goulburn 1 Gourock Range 4, 5, 10 Great Dividing Range 119 Grose Meadow Trig. Station 58 Gudgenby River 7, 76 Gungoandra Creek 10, 38, 39, 41, 49, 53, ISS, 196, 238 Gungoandra Gap 31, 180, 181, 191, 196 250 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET Gungoandra Siltstone Member 13, 1St, 19t, 25t, 31-32, 130, 184 Hanging Rock 200, 240 "Hanging Rock Limestone" 200 Harrisons Peak 107, 108 Harrisons Peak Granite 17, 23t, 27, 71, 74t, 107-109, 110, 111 "Harrisons Peak Massive Microc1ine Granite" 108 Hill End Trough 150 Honeysuckle Creek 81 Hoskinstown 13, 16, 26, 27, 55, 57, 64, 65, 68 Hoskinstown Group 13, 1St, 16, 25t, 55-69, 145 I-type granite 17, 71, 7lt, 72, 72t, 73, 74t "Igneous Series" 38 "Inge1ara" 198 Inge1ara Creek 33, 193 Initia1 Cowra Trough 148 Jerang1e 1, 6, 10, 17, 30, 33, 34, 35, 36, 41, 56, 59, 90, 90p, 97, 114, 115, 116, 118, 123, 124, 125, 126, 138, 139, 139p, 149p, 152, 178, 179, 180, 187, 188, 231, 232 "Jerang1e Granite" 98, 114 "Jerang1e Granite Complex" 114 "Jerang1e Grey Granite" 114 Jerang1e Igneous Complex 5, 17, 23t, 73, 99, 104, 105, 114-119, 126, 142, 145, 213-214 Jerrabomberra Creek 3 Jerrawa Beds 26 Jinero Fault 145 Jingera Trig. Station 59 Kanga Fault 67, 145 Kanimblan Tectonic Stage 151 Keatings Shale Member 62 "Keewong - Micaligo Porphyry Complex" 45 "Keewong Porphyry" 45 Keewong Trig. Station 47 Kiandra Beds 22 Kohinoor rhyodacitic-dacitic facies 60, 61 Kohinoor Trig. Station 59, 61, 62 "Kohinoor Tuffs" 60 Kohinoor Volcanics 13, 1St, 16, 19t, 25t, 55, 59-64, 65, 66, 67, 68, 125, 127, 131, 145, 150, 205 "Kohinoor Volcanics Group" 60 "Koo1ambah" 95 Koo1ambah Adamellite 24t, 74t, 90, 95-96, 113, 208, 226 Kosciusko Batholith 72 Kosciusko phase 11, 146, 152 Krawarree 10 Kuroko-type sulphide deposits 150 Lachlan Fold Belt 13, 72, 133, 147,151 Lachlan Geosyncline 130 Lachlan Mobile Zone 147 Lachlan - Pre - Cratonic Province 147-151 Lake Bathurst 119 Lake Burley Griffin 3 Lake George 114, 137, 144, 234 Lake George Fault 137 Lake George Mines Pty Ltd 6, 57, 59, 60, 65, 153 "Lanyon" 200 Late Cretaceous - Cainozoic Tectonic Stage 147, 152 "Limekiln Granodiorite" 98, 100 Limekiln Group 98 limestone 24t-25t, 33-35, 42, 48, 49, SOp-SIp, 56, 57, 59, 130, 138, 143, 150, 153, 155, 185-200, 238-240 Livingstone Porphyry 16, 24t, 45, 54p, 55, 85-86, 87, 206-207 Livingstone Trig. Station 86, 195 Lobbs Hole Creek 43 "Lockhart igneous complex" 120 London Bridge 1, 35, 36p, 113, 239 "London Bridge" 33, 35, 112, 185, 186 "London Bridge Formation" 33 "London Bridge Limestone" 33 "London Bridge Massive Quartz Porphyry" 112 Long Flat 124 Maragle Batholith 72 marble 38, 49, 155 "Marble Mine Limestone" 199 Margarets Creek 195 Meriangaah Siltstone 184 metallic deposits Bredbo copper-si1ver-lead mine 153 Captains Flat orebody 145 chalcopyrite 29, 56, 126 Co1inton sulphide deposit 153 metallic deposits (cont.) copper 153 E11iots gossan 59, 62 Federal mine 153 Fox1ow gold prospect 154 gold 151, 153 Golden Crown reefs 153 "I1verton" gossan 153 iron 154 Kohinoor mine 59 Lake George mine 6, 61, 62, 63, 145, 153 lead 153 Miche1ago copper prospect 197 Miche1ago iron quarry 197 Miche1ago sulphide deposit 153 molybdenum 73, 111 pyrite 29, 56, 82, 126, 127, 130, 131 silver 153 sulphides 137, 153 zinc 153 "Micaligo" 30, 94, 95, 183, 184, 185 Mica1igo Adamellite 24t, 73, 74t, 90, 91, 94-95, 208, 225 Mica1igo Creek 10, 86, 92, 199 "Mica1igo Porphyry" 45 Miche1ago 1, 4t, 5, 6, 13, 16, 28, 35, 38, 41, 44, 45, 47, 48, 53, 55, 85, 89, 105, 106, 109, 113, 129, 138, 143, 147, 149, 150, 153, 154, 155, 183, 194, 197, 229, 239, 240 "Miche1ago Batholith" 89 "Miche1ago Granite" 89 Miche1ago Igneous Complex 5, 17, 24t, 73, 74t, 89-97, 90p, 105, 106p, 112, 123, 137, 138, 207-209, 227 Miche1ago Railway Station 200 Mo1ong - South Coast Antic1inoria1 Zone 13, 133, 136-142, 153 Mo1ong Volcanic Rise 147, 148 INDEX 251 Mo1ong Fault 66, 67, 145 Mo1ong10 River 10, 63, 121, 123 Mo1ong10 Valley 121 Monaro Highway 1, 43, 45, 85, 86, 88, 89, 138, 143, 155, 185, 193, 194, 197 Monaro Province 152 Monaro region 11, 152, 153 Monaro Slope and Basin 147 Monke11an Granodiorite 24t, 74t, 90, 91, 92-93, 94, 207, 223 "Morley Formation" 38 Morley Member 38 Moruya Batholith 72 Mount Baldwin 61, 62, 65 Mount Bollard 121 Mount Campbell 4t Mount Clear 7, 76, 80, 124 "Mount Painter Porphyry" 45 Mount Roberts 1 Mount Tennent 82, 83, 84 "Mount View Adamellite" 98 Mount View Range Granodiorite 98 Mundoonen Sandstone 31, 130 Mundoonen Series 178 Murrumbidgee Batholith 16, 17, 21, 22, 25t, 53, 55, 71, 73, 74t, 75-85, 86, 126, 136-137, 141, 143, 146, 149, 151, 222, 242 "Murrumbidgee Bathy1ith" 75 Murrumbidgee Fault 10, 16, 44, 50p-51p, 52, 76, 77, 83, 88, 113, 136, 138, 143, 144, 242 Murrumbidgee River 7, 10, 16, 17, 48, 49, 52, 53, 54, 75, 82, 83, 85, 86, 87, 123, 124, 136, 143, 144, 154, 155, 198, 199, 238, 239, 240 Murrumbidgee Valley 4, 7, 10 Murrumbucka 218, 235 Murrumbucka Creek 79 Murrumbucka Gap 79, 80 Murrumbucka Tonalite 17, 25t, 73, 74t, 77, 78, 79-80, 218 Murrumbucka Trig. Station 79, 218 Mya11 Trig. Station 126 Naas Lake 124 Naas River 7, 76 Naas Road 155 "Norongo" 16, 17, 55, 56, 57, 59, 63, 113, 123, 145, 154, 155 Narongo Fault 10, 16, 21, 28, 30, 55, 56, 59, 99, 115, 118, 123, 123, 137, 141, 145, 155, 243 252 GEOLOGY OF THE MICHELAGO 1:100,000 SHEET "Newtown Beds" 65 Newtown Hill 69 Nimmo Trig. Station 22 non-metallic deposits clay 154 construction materials 154-155 gravel 155 railway ballast 154 sand 154-155 shale 154 Nungar Beds 14t, 22 Old Adaminaby 21, 22 Onslow Granodiorite 24t, 74t, 90, 91, 93-94, 95, 208, 224, 243, 244 "Orrora1" 21 Parish Abercrombie 238 Ballallaba 239 Bransby 48, 49, 238 Du11anamang 86 Burra 239 Cosgrove 124 Gungoandra 192, 238 Jinjera 178, 239 Micaligo 239 Monke11an 92, 200, 239, 240 Onslow 93 urialla 240 York 235 Peak View 116 Permian Tectonic Stage 151-152 Pokolbin 98 "Ponderose" 183, 194 Primrose Valley 13, 27, 30, 56, 57, 64, 113, 145 quartz reefs 138, 142 Queanbeyan 1, 4t, 5, 38, 45, 139, 154, 155, 239 Queanbeyan Fault 10, 137, 145 Queanbeyan River 1, 10, 17, 33, 36, 37p, 109, 110, 111,118, 123, 154 Quidong 143, 148, 184, 187, 190, 196 Quidongan Orogeny 136, 145, 149, 150 Quidongan Tectonic Stage 151 "Railway Slates" 26 Reedy Creek Flat 124 Rob Roy Trig. Station 43 Roberts Mountain 76 "Rocky Peak Granite" 119 Rocky Pic Anticlinorium 13, 17, 21, 26, 114-120, 129, 133, 136, 137 141-142 "Rocky pic Granite" 119 Round Hill 38 "Round Hill Granodiorite" 114 Round Hill Group 114 Round Hill Trig. Station 41 Roya11a 1, 3, 5, 16, 39, 41, 43, 45, 143, 153, 154, 155 "Rutledge Quartzite" 27, 56, 57, 58 Rutledge Quartzite Member 13, 25t, 57-58, 59, 131, 145 Rutledge Trig. Station 57, 58 Ryans (Wangrah) Creek 27, 91, 112, 126, 127 Ryrie Formation 13, 15t, 19t, 25t, 30-32, 36, 91, 130, 137, 138, 140, 149, 183-185, 202 Ryrie Trig. Station 28, 30, 182, 183, 185, 193, 194 Ryries Creek 183 S-type granite 17, 71, 71t, 72, 72t, 73, 74t "Sapling Flat Granite" 97, 98 Sapling Flat Gully 97, 99 Sapling Flat Igneous Complex 17, 23t, 28, 73, 74t, 97-103, 102p, 112, 113, 125, 137, 140, 209-210, 243 Scheele's house 180 "Scottdale" 41, 197 Shanahans Falls Creek 124 Shannons Flat 81, 220 Shannons Flat Adamellite 17, 21, 25t, 74t, 77, 79, 81-82, 83, 84, 137, 242 "Shannons Flat Granodiorite" 82 Sherlock Fault 142 Shoa1haven Fault 120 Shoa1haven River 5 Sinclair Conglomerate Member 15t, 16, 25t, 66, 67, 68 Sinclair Trig. Station 68 INDEX Slapup 115 South Coast 3 Southern Highlands 7, 17 Spring Vale Creek 80 "Spring Valley" 155, 198 State Circle Shale 31, 130, 149 Stewartsfie1d Granodiorite 78 Stockyard Creek 182 Tabberabberan Orogeny 136, 151 Tabberabberan Tectonic Stage 147,151 Tantangara Beds'148 Tantangara 1:100,000 sheet 7, 21, 76, 81, 84, 242 Tara1ga 187, 190 Tasman Epi-Cratonic Province 147,151-152 Tasman Fold Belt System 13 Tasman Mobile Zone 71 Teatree Creek 95 "Tea Tree Creek" 93 Tharwa 1, 10, 11, 16, 45, 48, 52, 53, 55, 82, 83, 131, 136, 151, 154, 155, 198, 200, 220, 221 Tharwa Adamellite 17, 25t, 74t, 77, 79, 81, 82-83, 84, 136, 221, 242 Tiger Cat Creek Fault 145 Tigercat Creek 60, 61, 127 Tinderry - Gourock Highlands 7, 10 Tinderry Granite 6, 17, 23t, 74t, 91, 105-107, 106p, 109, 110, Ill, 113, 146, 210-211, 229, 243 Tinderry Lineament 146 Tinderry Peak 1 Tinderry Range 4, 10, 28, 95, 105, 106, 106p, 118, 126, 229 "Tinderry Series" 33 Tinderry Trig. Station 105 Top Flats 124 tourmaline 23t, 27, 31, 80, 112, 201, 209 Town Hill 66, 68 Towneys Creek 117 Towneys Creek Adamellite 23t, 73, 74t, 114, 115, 116, 117-119, 214, 233, 244 253 Tuggeranong 43 "Tuggeranong Granite" 43 Tuggeranong Tuff Member 24t, 39, 43-44, 143 Uria11a Granite 17, 23t, 28,71, 74t, 107, 109-110, Ill, 113, 211, 230 "Urialla Granite" 109, III "Urialla Foliated Granite" 109 "Urialla Massive Microcline Granite" 109, III Urialla Trig. Station 109 "Urila" 109, 110, Ill, 113 Vanderbilt Hill 69, 200 Victoria 21, 114, 137 Wagga Marginal Basin 148 Wagga Wagga 148 Wangrah Adamellite 23t, 73, 74t, 98, 101-103, 112, 209, 231, 243 Wangrah Trig. Station 101 Watch Box Creek 110 Watch Box Granite 17, 23t, 73, 74t, 105 107, 108, 109, 110-112, 212 Westerly Muscovite Granite 83 Whinstone Basalt 17, 23t, 123,124-125 Whinstone Hill 125 Whiskers Fault 137 "Willandra" 182 Williamsda1e 1, 4t, 45, 46, 47, 52, 131, 150, 154 Wil1iamsdale Volcanics 1St, 16, 18t, 24t, 45-48, 131, 137, 150, 154, 203-204, 237 Willoona Tonalite 77, 78 Yandyguinu1a Creek 67, 121 Yandyguinula Member 1St, 16, 25t, 66, 67 Yaouk Leucogranite 83 Yass 26, 178, 187, 190, 197