Geology and Prospectivity of the Bairnsdale 1:250 000 Map Sheet Area
Total Page:16
File Type:pdf, Size:1020Kb
VIMP Report 37 Geology and prospectivity of the Bairnsdale 1:250 000 map sheet area S. Maher, M.A. Hendrickx, R.J. Boyle and D.J. Brookes October 1996 Bibliographic reference: MAHER, S., HENDRICKX, M.A., BOYLE, R.J., BROOKES, D.J., 1996. The geology and prospectivity of the Bairnsdale 1:250,000 map sheet area. Victorian Initiative for Minerals and Petroleum Report 37. Department of Natural Resources and Environment. © Crown (State of Victoria) Copyright 1996 Geological Survey of Victoria ISSN 1323 4536 ISBN 0 7306 9407 0 This report may be purchased from: Business Centre, Department of Natural Resources and Environment, Ground Floor, 115 Victoria Parade, Fitzroy, Victoria 3065 For further technical information contact: Manager, Geological Survey of Victoria, Department of Natural Resources and Environment, P O Box 2145, MDC Fitzroy, Victoria 3065 Authorship and acknowledgments: Authorship responsibilities for this report are as follows: Chapter 1 S. Maher Chapter 2 M. Hendrickx Chapter 3 S. Maher, R. Boyle (Omeo 1:100 000 map area) Chapter 4 D. Brookes, S. Maher Chapter 5 M. Hendrickx Chapter 6 M. Hendrickx, S. Maher Information in the Bairnsdale Mine Database was compiled by S. Maher and R. Boyle (Omeo 1:100 000 map area). Ideas in Chapters 3 and 6 were developed following discussion with K. Slater, R. Twyford, S. Haydon, D. Moore and F. VandenBerg. Figures 1, 2, 3 and 4 were produced by R. Jolly and J. Dunleavy. Figures 5, 6 and 7 were produced by D. Brookes. Editing was by R. Buckley and P. O'Shea. Formatting was by G. Ellis. GEOLOGY AND PROSPECTIVITY - BAIRNSDALE 1 Contents Abstract 3 1 Introduction 4 2 Geology 6 2.1 Geological history 7 Lachlan Fold Belt 7 Mid-Cretaceous to the present day 10 2.2 Stratigraphy-sedimentary and volcanic rocks 10 Ordovician 10 Silurian 12 Lower Devonian 13 Upper Devonian-Carboniferous 14 Permian 14 Triassic 14 Cretaceous 15 Tertiary 15 Quaternary 15 2.3 Intrusive Rocks 15 Bega Basement Province 15 Wagga Basement Province 16 Kosciusko Basement Province 18 Howqua Basement Province 20 3 Economic geology 22 3.1 History of mining 22 3.2 Mineral Production 25 3.3 Precious metal vein deposits 27 Harrietville-Dargo gold province 30 Benambra gold province 34 3.4 Lower Devonian volcanic hosted metal deposits 36 3.5 Placer gold deposits 40 3.6 Silurian volcanic associated massive sulphide (VAMS) deposits 42 3.7 Porphyry copper deposits 43 3.8 Base metal vein deposits 46 3.9 Red bed copper deposits 47 3.10 Carbonate hosted metal deposits 47 3.11 Nowa Nowa ironstones 49 3.12 Granite hosted tin deposits 50 3.13 Wolframite vein deposits 51 3.14 Brown coal deposits 51 3.15 Non metallics 51 Limestone 51 Dimension Stone 52 Pyrophyllite 52 Barite 52 Talc 53 Semi-precious gemstones 53 Dolomite 53 Feldspar 53 Wollastonite 54 4 Overview of mineral exploration 55 4.1 Gold 55 4.2 Base metals and silver 55 4.3 Other minerals and coal 56 4.4 Soil and stream sediment geochemistry 57 5 Geophysics 58 2 GEOLOGY AND PROSPECTIVITY - BAIRNSDALE 6 Mineral resource potential and prospectivity 59 6.1 Precious metal vein deposits 59 6.2 Lower Devonian epithermal precious metal deposits 60 6.3 Placer gold deposits 61 6.4 Silurian volcanic associated massive sulphide (VAMS) deposits 62 6.5 Porphyry copper-gold deposits 62 6.6 Base metal vein deposits 64 6.7 Red bed copper - uranium 64 6.8 Carbonate hosted base metal deposits 64 6.9 Tennant Creek style copper-gold deposits 64 6.10 Granite hosted tin deposits 64 6.11 Skarns 65 6.12 Heavy mineral sands 65 6.13 Industrial minerals 65 6.14 Diamonds 65 6.15 Buried intrusions 65 References 67 Appendix 1 75 Bairnsdale 1:250 000 map area: Summary of Exploration Licences Appendix 2 82 Bairnsdale 1:250 000 map area: Location of expired Exploration Licences Victorian Initiative for Minerals and Petroleum (VIMP) report series 98 List of figures 1 Recent airborne geophysical surveys and geological mapping, Bairnsdale 1:250 000 map area 5 2 1:500 000 simplified geology, Bairnsdale 1:250 000 map area. (Back pocket) 3 Geology, mineral resources and tenements, Bairnsdale 1:250 000 map area. (Back pocket) 4 Mineral resources within the Bairnsdale 1:250 000 map area 23 5 Primary, alluvial and total goldfield production 28 6 Annual primary and alluvial goldfield production 29 7 Source of gold production 30 8 Gold vein orientations, Bairnsdale 1:250 000 map area 32 9 Cassilis mine, c.1910. Photo, Minerals & Petroleum Victoria collection 35 10 Exploration drilling at Benambra by WMC, c.1975. Photo, Minerals & Petroleum Victoria collection 42 11 TMI image showing mineral resources of the Bairnsdale 1:250 000 map area. (Back pocket) List of tables 1 Summary of the geological history, stratigraphic units and mineralising events within BAIRNSDALE 8 2 Production from mines within BAIRNSDALE 26 3 Production from the Wilga deposit 26 4 Gold production from goldfields within BAIRNSDALE 27 5 Sources used in calculating gold production within BAIRNSDALE 30 6 Major primary gold producers within goldfields of the Dargo-Harrietville gold province 31 7 Major primary gold producers within goldfields of the Benambra gold province 35 8 Major alluvial gold producers within goldfields of BAIRNSDALE 40 GEOLOGY AND PROSPECTIVITY - BAIRNSDALE 3 Abstract This report summarises the geology and prospectivity of the Bairnsdale 1:250 000 map area (BAIRNSDALE) in eastern Victoria. New airborne geophysics and detailed geological mapping conducted over BAIRNSDALE as part of the Victorian Initiative for Minerals and Petroleum (VIMP) has enabled a reappraisal of the regional geology and prospectivity of the area. This has been complemented by mineral resource, mineral exploration and exploration geochemistry compilations. Broad areas with potential to host a variety of styles of mineralisation have been outlined as a result of this reappraisal. These include: · porphyry copper–gold deposits associated with high level magnetic intrusions; · epithermal precious metal deposits associated with the Snowy River Volcanics and Mount Elizabeth Caldera Complex; · precious metal vein deposits within and outside goldfields; · additional Wilga style volcanic associated massive sulphide deposits within the Limestone Creek Graben; · Tennant Creek style copper–gold deposits in Nowa Nowa ironstones; · Irish style base metal deposits in the Buchan Rift; · base metal veins associated with caldera fractures; · red bed copper–uranium; · granite hosted tin deposits; · placer gold; and · a variety of industrial minerals. 4 GEOLOGY AND PROSPECTIVITY - BAIRNSDALE 1 Introduction parks and roads. This data set is available from the Geological Survey of Victoria. This report summarises the geology, mineral resources and mineral exploration history of the Bairnsdale 1:250 000 map area (BAIRNSDALE) in East Victoria (Fig. 1). This information is designed to aid mineral exploration and mineral resource development. It complements new geological maps and airborne magnetic and radiometric data covering large parts of BAIRNSDALE that have been collected as part of the Victorian Initiative for Minerals and Petroleum (VIMP). New geological maps cover the Orbost 1:100 000 map area (VandenBerg et al., 1996), the Mount Elizabeth Caldera Complex (Simpson et al., 1995), the Limestone Creek area (Allen, 1991) and the Murrindal 1:100 000 map area (Orth et al., 1995). Geological interpretation of the new VIMP airborne geophysical data is presented in Sands (1995) covering the Orbost area, Slater (1996) covering the Dargo area, Haydon (1996) covering the Omeo area, and Twyford (1996) covering the Murrindal area. Mineral exploration in BAIRNSDALE, including details on anomalies in geochemical surveys and significant drill intersections, is summarised in Brookes and Boyle (1996). Detailed location, production and geological information for mines and prospects within BAIRNSDALE accompany this report in the BAIRNSDALE Mine Database. The database, explanatory notes and references are supplied on a 3.5 inch DOS disk in the following formats: BAIRNSDALE Mine Database Bairmine.mdb Microsoft Access 2.0 format Bairmine.ldb Microsoft Access 2.0 format *.txt Tab delimited ASCII text files derived from the Access Database Explanatory Notes Readme.doc Microsoft Word 6.0 format Readme.txt ASCII text file format References Referenc.doc Microsoft Word 6.0 format Referenc.txt ASCII text file format The mine database is only one theme in the GIS data set covering BAIRNSDALE. Other themes include geology, geochemistry (also available in ASCII text and relational database formats), magnetic and radiometric images, current and expired Exploration Licences (ELs), national 6 GEOLOGY AND PROSPECTIVITY - BAIRNSDALE 2 Geology Ordovician and Silurian turbidite sequence that has been deformed during the Quidongan and Tabberabberan deformations. The BAIRNSDALE encompasses a diverse group of Wonnangatta Fault is an important structure rocks deposited in a variety of environments running northwest through the zone. It divides between the Lower Ordovician and Quaternary. the zone into two domains with differing The eastern part of the map sheet, covered by structural styles (Gray et al., 1988). The the MURRINDAL (Orth et al., 1995) and domain southwest of the Wonnangatta Fault ORBOST (VandenBerg et al., 1996) 1:100 000 includes Pinnak Sandstone and Silurian map sheets and MOUNT ELIZABETH Cobbannah Group (Fergusson, 1996). One (Simpson et al., 1996) and LIMESTONE main phase of folding is present. The CREEK (Allen, 1991) 1:50 000 sheets has been enveloping surface is subhorizontal and mapped in detail and it is mainly from these vergence is to the south. The style of reports that this summary of the geology has deformation indicates thin skinned fold thrust been derived. deformation associated with tectonic transport to the south (Gray et al., 1988). This is BAIRNSDALE straddles parts of the probably towards the Governor Fault which Mallacoota, Omeo, Tabberabbera and Buchan occurs at the southwest margin of the structural zones (Figs 2 & 3) which are four of Cobbannah Group under the Avon seven major Palaeozoic structural zones within Synclinorium as indicated by magnetic data the southeastern part of the Lachlan Fold Belt.