VIMP Report 4 The geology and prospectivity of the southern margin of the Murray Basin by M.D. BUSH, R.A. CAYLEY, S. ROONEY, K. SLATER, & M.L. WHITEHEAD March 1995 Bibliographic reference: BUSH, M.D., CAYLEY, R.A., ROONEY, S., SLATER, K., & WHITEHEAD, M.L., 1995. The geology and prospectivity of the southern margin of the Murray Basin. Geological Survey of Victoria. VIMP Report 4. © Crown (State of Victoria) Copyright 1995 Geological Survey of Victoria ISSN 1323 4536 ISBN 0 7306 7412 6 This report and attached map roll may be purchased from: Business Centre, Department of Agriculture, Energy & Minerals, Ground Floor, 115 Victoria Parade, Fitzroy 3065 For further technical information contact: General Manager, Geological Survey of Victoria, P O Box 2145, MDC Fitzroy 3065 Acknowledgments The preparation of this report has benefited from discussions with a number of colleagues from the Geological Survey of Victoria, notably David Taylor, Alan Willocks, Roger Buckley and Iain McHaffie. The authors would also like to thank Gayle Ellis for the formatting and Roger Buckley for the editing of this report. GEOLOGY AND PROSPECTIVITY - SOUTHERN MARGIN MURRAY BASIN 1 CONTENTS Abstract 3 1 Introduction 4 2 Geological history 5 2.1 Adelaide Fold Belt 5 2.2 Lachlan Fold Belt 5 3 Summary of rock units 8 3.1 Early to Middle Cambrian (The Glenelg Zone) 8 3.2 Middle to Late Cambrian (The Glenelg Zone and the Stawell Zone) 8 3.3 Cambro-Ordovician (The Stawell Zone) 9 3.4 Ordovician (The Glenelg Zone) 10 3.5 Ordovician (The Bendigo-Ballarat Zone) 10 3.6 Late Silurian/Early Devonian 10 3.7 Devonian 11 3.8 Permian 13 3.9 Post-Palaeozoic cover rocks fringing the Murray Basin 13 4 Geophysical Interpretation 14 4.1 Geophysical data and presentation 14 4.2 Interpreted lithological units 14 4.3 Structure 20 5 Basement modelling from boreholes 21 6 Economic Geology 23 6.1 Gold 23 Development of the Primary Gold Deposits 25 Development of the Alluvial Deposits 27 6.2 Base Metal Mineralisation 38 6.3 Other Metals 39 6.4 Uranium 40 6.5 Mineral Sands 41 6.6 Gypsum 43 6.7 Bentonite 43 6.8 Coal 45 6.9 Gemstones, Precious & Semi-Precious Stones 45 7 Summary of exploration 46 7.1 History of exploration 46 7.2 Major exploration programmes 47 8 Prospective areas 54 References 58 Appendix 1 72 Mine Locations. Appendix 2 98 Location of expired exploration licences Appendix 3 110 Summary of exploration targets within the North West VIMP area Appendix 4 117 Exploration licence summary: North West VIMP area Victorian Initiative for Minerals and Petroleum (VIMP) report series 122 2 GEOLOGY AND PROSPECTIVITY - SOUTHERN MARGIN MURRAY BASIN Figures 1 Distribution of major Palaeozoic rock units and tectonic provinces 2 Cross sections: the Palaeozoic rocks outcropping across the southern margin of the Murray Basin (back pocket) 3 TMI pseudocolour image with NE shading 4 Location of 1:100 000 mapsheets 5 Borehole location and basement lithology, southern margin of the Murray Basin (back pocket) 6 Basement image from boreholes, southern margin of the Murray Basin (back pocket) Tables 1 Devonian granites 2 Airborne surveys carried out over the southern margin of the Murray Basin 3 Major lithological units interpreted from geophysical data 4 Significant recorded gold production 5 Average composition and resources, WIM 150 deposit 6 WIM deposits resource details 7 CRAE drill hole summary Maps (attached map roll) 1 Geology, mineral deposits & tenure - Horsham 1:250 000 sheet 2 Geology & mineral deposits - St Arnaud and part Ballarat 1:250 000 sheets 3 Tenure - St Arnaud and part Ballarat 1:250 000 sheets 4 Geology, mineral deposits & tenure - Swan Hill 1:250 000 sheet 5 Geophysical interpretation of the Horsham 1:250 000 sheet 6 Geophysical interpretation of the St Arnaud 1:250 000 sheet 7 Geophysical interpretation of the Swan Hill 1:250 000 sheet 8 Total magnetic intensity contours - Horsham 1:250 000 sheet 9 Total magnetic intensity contours - St Arnaud 1:250 000 sheet 10Total magnetic intensity contours - Swan Hill 1:250 000 sheet 11Depth to basement contours and basement lithology - Horsham 1:250 000 sheet 12Depth to basement contours and basement lithology - St Arnaud 1:250 000 sheet 13Depth to basement contours and basement lithology - Swan Hill 1:250 000 sheet GEOLOGY AND PROSPECTIVITY - SOUTHERN MARGIN MURRAY BASIN 3 Abstract The geology and prospectivity of the southern margin of the Murray Basin has been summarised to provide information to explorers making application for tender areas in the North West VIMP initiative area. The exemption on granting mining and exploration licences within the North West VIMP initiative area will be partially lifted during the tender process. Tender areas have only been defined around the south eastern part of the initiative area. The remainder of the initiative area will be available for licence applications submitted by the standard process. Regions with potential to host previously unidentified gold and/or base metal mineralisation have been outlined. These were identified by detailed interpretation of existing company airborne geophysical data, summary of recent company exploration work, compilation of mineralisation styles within goldfields and other commodities, modelling of Murray Basin sediment cover over Palaeozoic basement, together with the results of recent surface mapping in areas adjacent to the North West VIMP initiative area. Many of these prospective areas are possible repetitions of the styles of mineralisation observed in the flanking Palaeozoic, and have been relatively unexplored due to poor exposure or blanketing by sediments of the Murray Basin. Structural characteristics such as regional structural highs and brittle faults and fractures have been identified as features focusing gold mineralisation. Other geological environments known to host gold include quartz free auriferous dark carbonaceous slates, greenstone hosted gold and base metals, granite hosted gold and Stawell-type mineralisation. Known goldfields still represent attractive exploration targets. All currently operating gold mines in Victoria are within historical goldfields and have often doubled previous past production. Thumbprint magnetic anomalies also present potential primary diamond targets under an overburden of barren Murray basin sediments. Potential also exists for additional mineral sands, brown coal and bentonite resources within the Murray Basin sediments as well as additional near surface gypsum deposits. 4 GEOLOGY AND PROSPECTIVITY - SOUTHERN MARGIN MURRAY BASIN 1 Introduction report area. An interpretation of the geophysical data is presented in Chapter 4 whilst Chapter 5 outlines the basement This report represents part of a data package modelling derived from borehole data. The which includes the results of airborne history of mining and description of geophysics flown as part of the North West mineralisation styles are discussed in Chapter 6 VIMP initiative programme. The package has and a brief summary of exploration conducted been prepared to coincide with a call for tenders to date given in Chapter 7. A brief outline of for exploration licences around the south the economic potential and prospectivity of the eastern part of the initiative area. Tender areas southern margin of the Murray Basin is have only been outlined around this south presented in Chapter 8. eastern part of the initiative area. The remainder of the initiative area will be The map roll attached to this report includes available for licence applications submitted by maps outlining the geology, mineral deposits, the standard process. The location of tender tenure, total magnetic intensity, geophysical areas is shown in the flyer in the back pocket. interpretation and depth to basement modelling for each of the Horsham, St Arnaud and Swan This, and subsequent data packages are Hill 1:250 000 mapsheets. intended to provide summary information to explorers making exploration licence In the body of the report mapsheet titles have applications in areas released in the North West been abbreviated so that 1:250 000 mapsheets VIMP and Eastern Highlands VIMP initiative appear as ST ARNAUD, for example, and areas. 1:100 000 mapsheets appear as ST ARNAUD. The reference list directs the reader to more This report presents a summary of the geology, detailed descriptions of the geology and geophysics, mineralisation and exploration mineralisation of the area. This listing is history of the southern margin of the Murray ordered by bibliographic reference number and Basin. The report area concentrates on the the references quoted in the report includes this Horsham, St Arnaud and Swan Hill 1:250 000 number in square brackets. mapsheets (Figs. 1 and 4) which comprise the southeastern section of the North West VIMP initiative area. Shallow thicknesses of Murray Basin sediments overly the Palaeozoic basement over much of this area. The geophysical interpretation focuses on the pre-existing company data which covered the majority of these mapsheets. A preliminary appraisal of the new airborne geophysical data collected for the remainder of the North West VIMP initiative area as part of the VIMP programme is presented in Willocks (1995, [21445]). A complete outline of the work conducted within Exploration Licences in the North West VIMP initiative area is presented in Rooney (1995, [21373]). The report aims to detail the styles of primary mineralisation within the fringing Palaeozoic basement as well as areas within the Murray Basin where the depth of sedimentary cover overlying Palaeozoic basement is less than 150 m. Areas prospective for primary mineralisation have been outlined and combined with images developed from the airborne geophysical data. Chapter 2 gives an overview of the geological history, whilst Chapter 3 outlines the stratigraphy of the GEOLOGY AND PROSPECTIVITY - SOUTHERN MARGIN MURRAY BASIN 5 2 Geological history Ma old (i.e. Cambrian), and therefore have strong affinities with the Kanmantoo Group of South Australia. Summary Late Cambrian-Early Ordovician Delamerian The geological history of the southern margin of Deformation and intrusion of syn- and post- the Murray Basin, and the western district of orogenic granite masses.