Mineral Resources Tasmania Tasmanian Geological Survey Tasmania DEPARTMENT of INFRASTRUCTURE, Record 2004/03 ENERGY and RESOURCES Updating and revision of the 1:25 000 scale series geological maps covering the Mt Read Volcanics belt in western and northwestern Tasmania K. D. Corbett Introduction Because the revision of Rcodes involved a statewide database, with flow-on effects to maps outside the This report represents the culmination of a two-stage project area, it was necessary to fully complete the project carried out by the author under the Western revision and updating process for all the project maps Tasmanian Regional Minerals Program (WTRMP) to before the new system could be implemented. The revise and update the series of published 1:25 000 scale revised maps and Rcodes have been presented to geological maps of the Mount Read Volcanics belt Mineral Resources Tasmania, but actual through western and northwestern Tasmania. In implementation of the changes will involve particular, advances in understanding and knowledge of the geology of this belt gained through study of considerable time for re-drafting. WTRMP geophysical surveys (aeromagnetics and (Note added in proof by G. R. Green: The revisions radiometrics) and associated geological mapping, suggested here represent a thorough review and a from recent work by exploration companies in the major advance in the understanding of the geology of area, and from recent University research in the area, the Mount Read Volcanics and adjacent rocks by was to be shown on the maps. Much of this work had Dr Corbett. Most, but not all, have been implemented been summarised in a previous series of WTRMP on the 1:25 000 scale digital compilations after reports (Corbett, 2002, 2003; Corbett and subsequent review by MRT geologists and further McClenaghan, 2003; Morrison, 2002) and on three research and limited field checking by M. J. Vicary. specially produced 1:100 000 scale geological maps, However, it is considered important to preserve the but it was considered necessary to have the views of the author of this report. Hence, the information represented on the mainstream digital recommendations for changes to the maps presented map products. herein are entirely those of Dr Corbett, but there has Some 36 map sheets have consequently been revised been minor editing of the text.). and updated, with new boundaries in some cases, including some large areas of completely new Stages in the revision project mapping, and new legends in all cases. In addition, there has been an extensive reorganisation of Stage 1 stratigraphic Rcodes* and mnemonics, with the The 13 published map sheets of the Central West area addition of many new stratigraphic units, the (Darwin to Ramsay) were revised and updated with replacement of many existing units, and the new boundaries and correlations, and new legends re-combination of many units. were drawn up. A list of new Rcodes and mnemonics Many of the geological changes flow through to the was prepared, and most of these were entered into the 1:250 000 scale maps of the area, and some revisions to Rcode database by Dr M. P. McClenaghan, although boundaries, legends, Rcodes and mnemonics are some were deferred pending work in the northwest proposed for these maps. and southwest areas. * Both the 1:25 000 and 1:250 000 scale digital geology data use RCODE — each scale has a separate coding system. RCODE is a unique number given to each rock unit and is used as a link to the geology lookup tables GEOL25.LU or GEOL250.LU or GEOL500.LU and LITH.LU. RCODE is also used to record the rock or mineral type of veins or dykes. Tasmanian Geological Survey Record 2004/03 1 This stage was carried out in the period August to The final phase of Stage 2 involved the preparation of a October, 2003. The revised maps were held by the Data preliminary new colour design for the 1:25 000 scale Management Branch, but no revisions were carried out maps, to take account of the geological changes, and pending completion of the northwest and southwest the preparation of this report, in which the major map maps. revisions are listed, and the overall findings of the project in terms of advances in understanding and Stage 2 presentation of West Coast geology are described. Stage 2 was carried out over the period March to June, The ten published map sheets (excluding the 2004. previously done Charter) in the northwest sector (Parrawe to Gog), and 13 of the 15 published sheets in Acknowledgements the southwest sector (two did not require revision) The author is again pleased to acknowledge the were revised and updated, with new legends drawn encouragement and helpfulness of MRT staff, and new Rcodes prepared. An integrated complete set particularly Dr Geoff Green, who supervised and of revised 1:25 000 scale Rcodes and mnemonics, supported the project; Dr Marcus McClenaghan, who including units from the Central West, was completed assisted with the difficult and time-consuming process with the assistance of Dr M. P. McClenaghan of MRT of entry, scrutiny and checking of Rcodes; and Chris and M. J. Vicary (WTRMP contractor). Revisions were Meech, who assisted with the supply of maps and also made to the legends and Rcodes of the Southwest much useful advice. Michael Vicary, WTRMP and Northwest 1:250 000 scale maps to accommodate contractor, is thanked for his enthusiastic participation the geological changes and revisions, but the necessary in discussions of the geology, and assistance with boundary changes have not yet been implemented. Rcodes. PARRAWE GUILDFORD LOONGANA WILMOT SHEFFIELD PEARSE LEA CETHANA GOG PENCIL RAMSAY CHARTER PINE PARSONS BLOCK ROSEBERY TULLAH DUNDAS SELINA OCEANA TYNDALL GORMANSTON OWEN DARWIN TABLE PHILIPS HEAD ALBINA SARAH VARNA BIRCHS WTRMP area HIBBS D’AGUILAR E & W ENDEAVOUR INNES Central west map series E & W MONTGOMERY MOORES Northwest map series MAINWARING OSMUND Southwest map series VERIDIAN LEWIS N & S Tasmanian Geological Survey Record 2004/03 2 Revisions to the 1:25 000 scale map sheets The many revisions made to the map sheets are listed 0 Owen Group unit at Gooseneck Hill assigned to below. Lower Owen after WTRMP study. The following abbreviations are used hereafter: 0 revision of Owen Group mnemonics. EQPS = Eastern Quartz-Phyric Sequence Tul lah CVC = Central Volcanic Complex 0 WVSS = Western Volcano-Sedimentary Sequence unit of feldspar-phyric CVC-type lava added in EQPS north of Mt Murchison, after WTRMP studies, Central West Map Series confirming interfingering relationship between CVC and EQPS in this area. Dar win 0 0 boundary of Granite Tor granite modified from designation of eastern sequence changed from WTRMP geophysics and reconnaissance mapping EQPS to Tyndall Group after WTRMP studies by by M. P. McClenaghan. Morrison (2002) and Corbett (2002). 0 revision of Owen Group mnemonics. 0 andesite body at Garfield prospect extended, after mapping by RGC Exploration. Block 0 revision of mnemonics–Rcodes for Owen Group 0 major area of new Aberfoyle Resources mapping units. (Richardson, 1994) added northeast of Mt Block. 0 compilation errors in Siluro-Devonian rocks in Lake 0 revision of Henty Fault Zone geology in Lake Burbury area rectified. Mackintosh area after WTRMP mapping (KDC). 0 new mapping added in Boco Road–Pinnacles area Owen 0 from Pasminco (McNeill, 2002) and thesis by R. O. area of new mapping at Little Owen Spur added Reid (1990). from WTRMP study and M.Sc. mapping (Corbett, 0 revision of Granite Tor granite boundary by 2001b). M. P. McClenaghan. 0 eastern sequence at Jukes Proprietary changed to 0 Tertiary basalt boundary extended at Mt Romulus Tyndall Group. from WTRMP geophysics. 0 revision of Owen Group mnemonics. Char ter 0 compilation errors corrected in Ordovician– Silurian–Devonian rocks in Lake Burbury area. 0 large area (50 km2) of new mapping by Aberfoyle Resources (Richardson, 1994) in Que–Hellyer–Mt Gor mans ton Charter area added, simplifying previous mapping 0 major addition of new geology over 18 km2 in Mt to some extent. Lyell mines area from M.Sc. mapping (Corbett, 0 large area of sedimentary rocks in lower Que River– 2001a, b), and clarification of geology in this area, Hatfield River area assigned to Tyndall Group including setting of Comstock and North Lyell chert correlates, underlain by Southwell Subgroup bodies within hydrothermal alteration zone. correlates (part of WVSS) and overlain by marine 0 many topographic and prospect names Owen Group correlates. recommended for inclusion. Oceana 0 revision of Owen Group mnemonics. 0 western part of White Spur Formation and western Tyn dall part of Henty Fault Wedge sequence (with andesitic-basaltic volcanic rocks) re-assigned to 0 very minor changes only Tyndall Group correlates, after work summarised in 0 small outcrop of granite added at Lake Dora after Corbett (2002). WTRMP study by KDC and KLM. 0 remainder of White Spur Formation and Henty 0 dip on Whitham Fault added. Fault Wedge sequences, plus Yolande River 0 number of topographic names recommended for Sequence, all grouped as WVSS, achieving much inclusion. simplification. 0 southern continuation of ‘Rosebery Group’ Selina sequence around Farrell Rivulet–Tom Creek 0 dyke of Devonian lamprophyre added at Red Hills designated as marine Owen Group, together with after WTRMP studies (KDC and KLM). sequence in area east of Professor Range. 0 eastern sequence confirmed as EQPS after WTRMP 0 small area of Pioneer Beds/Moina Sandstone added studies (KDC, KLM). in western tributary of Ewart Creek, unconformably Tasmanian Geological Survey Record 2004/03 3 overlying marine Owen Group, after mapping by 0 the mafic greywacke sequence on the south ridge off Berry (1996). Colebrook Hill is re-designated as Cleveland– 0 upper Dundas Group sequence in Mariposa Creek Waratah Association, after WTRMP studies area re-designated as marine Owen Group.