Exploration Field Workshop Cobar Region 2004
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Exploration Field Workshop Cobar Region 2004 Proceedings Edited by K.G. McQueen and K.M. Scott CRC LEME PUBLICATION Cobar 24-26 May 2004 © CRC LEME Copies of this publication can be obtained from: The Publications Officer, CRC LEME, c/- CSIRO Exploration and Mining PO Box 1130, Bentley WA 6102, Australia. Information on other publications in this series may be obtained from the above or from http://crcleme.org.au Cataloguing-In-Publication McQueen, K.G. and Scott, K.M.(Eds) Exploration Field Workshop Cobar Region 2004 Proceedings ISBN 0643068546 1.Geology 2. Landscapes 3. Mineral Exploration. 4. Central West New South Wales CRC LEME Published by: Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME), Perth, WA. Printed by: The University of Canberra Reference: MCQUEEN, K.G. AND SCOTT, K.M. (Eds), 2004. Exploration Field Workshop Cobar Region 2004, Proceedings. CRC LEME Report, Cooperative Research Centre for Landscape Environments and Mineral Exploration, Perth, WA. 107 pp Article Reference: BERTHELSEN, R. R. Exploration in the Cobar gold field: a 2004 perspective. In MCQUEEN, K.G. AND SCOTT, K.M. (Eds), Exploration Field Workshop Cobar Region 2004, Proceedings, pp5-9 PREFACE The Cobar region is a major metallogenic province within the Lachlan Fold Belt and remains highly prospective for further discoveries of significant mineral resources. Exploration in this region has been hampered by a complex regolith, with deep weathering and extensive transported cover components, as well as by the style and geometry of the deposits. This workshop aims to bring together geoscientists with knowledge of the region to present, discuss and exchange current ideas and experiences on the most effective approaches to exploration. The workshop will also showcase some of the results from the almost completed Girilambone (Cobar-Bourke) Project. This joint study by the Cooperative Research Centre for Landscape Environments and Mineral Exploration and the New South Wales Department of Mineral Resources has investigated the regolith and its geochemistry in the previously poorly known Girilambone terrain to the east of Cobar. A workshop format has been deliberately chosen to promote free and informal discussion. A large component of the workshop will be conducted in the field. The program will include an initial presentation session outlining the geological and regolith setting of the region followed by a half-day field trip to examine regolith materials, landscape features and exploration issues. There will then be a full day of presentation and discussion sessions based on the themes of exploration techniques and approaches and exploration case studies. This will be followed by a one-day field trip across the Girilambone terrain examining sites investigated by CRC LEME and the NSW DMR. The organising committee would like to thank the CRC LEME, the Cobar Branch of the AusIMM and SMEDG for underwriting the workshop. We also thank the corporate sponsors for their support as well as the presenters and attendees who will guarantee the success of the workshop. Thanks also to the various other people who have helped out behind the scenes. Particular thanks to Jenna Leonard who helped with compilation of the Proceedings volume. Organising Committee Convenors: Ken McQueen, Rex Berthelsen, Chris Torrey Scientific Program Keith Scott, Vlad David, Roslyn Chan Field Program Mike Hicks, Ian Stockton Social Program Roger Jackson Secretariat Judith Shelley, Jenna Leonard Proceedings Reviewers Maite LeGleuher, Bear McPhail, Ken McQueen, Ian Roach, Keith Scott, Lisa Worrall Ken McQueen and Keith Scott Major Sponsors Corporate Sponsors Also Polymetals Mining Services Pty Ltd Contents Page Benjamin R. Ackerman and Allan R. Chivas The surface geochemical expression of concealed mineralisation, Tritton copper deposit, 1 Girilambone district. Rex R. Berthelsen Exploration in the Cobar gold field: a 2004 perspective. 5 Phillip L. Blevin and Mel Jones Granites of the Bourke-Byrock -Brewarrina region. 10 Phillip L. Blevin and Mel Jones Chemistry, age and metallogeny of the granites and related rocks of the Nymagee region, NSW. 15 Peter M. Buckley A methodology for regolith-landform mapping in regional mapping programs. 20 Gary R. Burton, Steven J. Trigg and Mark W. Dawson A new bedrock mapping program for the Cobar-Bourke region 25 Adam Davey, John Joseph and Graham Heinson Electromagnetic profiling of paleochannels in the Girilambone region, NSW. 28 Vladmir David and Dick Glen The geological framework of the Cobar Basin. 31 A Duk-Rodkin, R.A. Chan and K.G. McQueen Drainage evolution of the Cobar region. 37 Michael G. Hicks and Guy Fleming Girilambone-Cobar Project: A collaborative venture between NSW DMR and CRC LEME. 43 Peter Leveret, Adam R. McKinnon and Peter A. Williams A supergene exploration model for Cobar style deposits. 46 Kenneth G. McQueen The nature, origin and exploration significance of the regolith, Girilambone-Cobar Region. 51 Kenneth G. McQueen and Dougal C. Munro Factoring in weathering-controlled chemical fractionation in surface sampling media. 57 Geoff Reed Exploring the Elura system. 62 Neil F. Rutherford The X-Y-Z of geochemical dispersion from mineralisation in the Cobar terrain 66 Keith Scott and Maite Le Gleuher Geochemical dispersion in the regolith, Girilambone belt region. 74 M. Skirka, V. David and I. Mackenzie The discovery and regolith expression of the Hera Au-Cu-Zn-Pb-Zn-Ag deposit. 78 Ian Stockton The strategy for geochemical exploration around the CSA mine. 83 S.E. Tate, R.S.B. Greene, K.M. Scott and K.G. McQueen The aeolian input to the Girilambone regolith-Implications for exploration. 94 Christopher E. Torrey and Peter D. White The Pipeline Ridge discovery. 101 M.A. Whitbread Using lithogeochemistry to explore in regolith dominated terrains: avoiding closure, background and weathering effects. 105 Author Index 109 Field Trip Guide and Locality Descriptions THE SURFACE GEOCHEMICAL EXPRESSION OF CONCEALED MINERALISATION, TRITTON COPPER DEPOSIT, GIRILAMBONE DISTRICT Benjamin R. Ackerman & Allan R. Chivas School of Earth and Environmental Sciences, University of Wollongong, Wollongong, NSW 2522 INTRODUCTION The Tritton Copper Deposit is located in the Girilambone District of New South Wales, in the central western portion of the Lachlan Orogen and at the eastern margin of the Cobar Basin. Tritton is 24 km south-west of Girilambone, which is approximately 620 km northwest of Sydney and 44 km from the town of Nyngan at 31o24’S and 146o43’E. Copper and gold mineralisation is hosted by metasediments of the Girilambone Group of Ordovician age, with other known deposits occurring elsewhere in the region at Girilambone, Hermidale and Tottenham. A resource of up to 9 Mt of ore has been identified by deep diamond drilling, conducted by previous co-owners, Nord Pacific Limited and Straits Resources Limited. Mining and development of the Tritton copper resource is underway under the direction of present owners and operators, Tritton Resources Limited. The present study examines the surface geochemical expression of mineralisation over the concealed Tritton Copper Deposit in regolith relatively undisturbed by prior mining activities. It is in effect a retrospective study granted that the position of sulfide mineralisation at depth has been well defined by exploration and resource delineation drilling. Previous geochemical investigations utilising samples from RAB drilling, vacuum drilling and soil surveys have identified spurious anomalous zones and failed to identify a convincing surface geochemical expression of the Tritton Copper Deposit. This study reports the multi- element geochemical expression of concealed mineralisation obtained by analysis of residual soils across the up-dip and up-plunge extension of known mineralisation and discusses the implications for geochemical exploration in the Girilambone district. GEOLOGY, MINERALISATION AND REGOLITH SETTING Tritton lithologies include strongly foliated, bedded and laminated quartz to quartzo-feldspathic sandstone, quartzite, shale, phyllite, chert and a number of small mafic volcanic units, and intrusive rocks (Figure 1). A series of late-stage Silurian to Devonian gabbroic dykes cross-cut other Girilambone lithologies in a NW orientation and low-grade metamorphism has resulted in low to moderate greenschist facies assemblages, with abundant chlorite, muscovite, sericite, quartz and minor epidote (Fogarty, 1998). Mineralisation at Tritton occurs in three zones, upper, central and lower, which are continuous for up to 450 m in strike length, up to 35 m wide and open at depth below 1000 m (Fogarty, 1998). The mineralisation strikes at approximately 028°, dips to the east at 20° to 70° and plunges to the south. Mineralisation of the upper zone is hosted by and wholly within a quartzite unit which continues to surface level, although the upper- most extent of mineralisation reaches to approximately 180 m below the present land surface (Figure 2). Primary mineralisation consists of massive pyrite and chalcopyrite, occurring as pipe-like massive sulfide zones, similar to the steeply dipping structurally controlled primary metal sulfide deposits of Girilambone Figure 1. Regional geological map of the and Girilambone North. Unlike the nearby Girilambone Tritton area. deposits, no secondary mineralisation is developed within the weathered profile of the Tritton Copper 1 Proceedings Exploration Field Workshop Cobar Region 2004 Deposit. Grades vary within the Tritton