An Appraisal of New Airborne Geophysical Data Over the Glenelg Region, North West VIMP Area, Victoria
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VIMP Report 14 An appraisal of new airborne geophysical data over the Glenelg region, North West VIMP area, Victoria K.R. Slater November 1995 Bibliographic reference: SLATER, K.R., 1995. An appraisal of new airborne geophysical data over the Glenelg region, North West VIMP area, Victoria. Victorian Initiative for Minerals and Petroleum Report 14. Department of Agriculture, Energy and Minerals © Crown (State of Victoria) Copyright 1995 Geological Survey of Victoria ISSN 1323 4536 ISBN 0 7306 7984 5 Keywords: Geophysics, magnetics, radiometrics, Hamilton SJ 54-7 mapsheet, Glenelg, Glenelg Zone, Glenelg River Group, Cambrian greenstones, Ordovician granites, Devonian granites. This report may be purchased from: Business Centre, Department of Agriculture, Energy & Minerals, Ground Floor, 115 Victoria Parade, Fitzroy, Victoria 3065 For further technical information contact: General Manager, Geological Survey of Victoria, Department of Agriculture, Energy & Minerals, P O Box 2145, MDC Fitzroy, Victoria 3065 Acknowledgments: The author wishes to thank Alan Willocks, Bruce Simons, Paul McDonald and Marc Hendrickx for discussions and editing provided for this report. Thanks also to Gayle Ellis for the formatting of this report and Sally Heeps and David Bibby for the diagrams. AIRBORNE SURVEY APPRAISAL - GLENELG 1 Contents Abstract 3 1 Introduction 4 2 Previous geophysics 6 3 Survey specifications 7 4 Data preparation 8 4.1 Data processing 8 4.2 Products 8 Hardcopy 8 Digital data 8 4.3 Future work 9 5 Geological appraisal 10 5.1 Summary of geophysical responses of main lithological units 10 5.2 Cambrian 11 Glenelg River Group 12 Volcanics 12 5.3 Ordovician 12 Plutonic rocks 12 5.4 Devonian 14 Plutonic rocks 14 Rocklands Rhyolite 14 5.5 Jurassic 14 Coleraine Trachyte 14 5.6 Cretaceous 14 Merino Group 14 Penola Trough 14 5.7 Tertiary 15 Older Volcanics 15 Heytesbury Group 15 Dorodong Sands 15 Laterite 16 5.8 Quaternary 16 Newer Volcanics 16 Paludal sediments 16 Malanganee Sands 16 Palaeo and present day channels 16 6 Structure 17 6.1 Structural features of greenstones and granites 17 6.2 Faults, fractures and dykes 17 6.3 Penola Trough and Kanawinka Fault 18 7 Mineral prospectivity 19 8 Conclusions 20 References 21 Appendix 22 Status of VIMP airborne surveys Victorian Initiative for Minerals and Petroleum (VIMP) report series 23 2 AIRBORNE SURVEY APPRAISAL - GLENELG List of Figures 1 Airborne survey coverage and locality map 5 2 Total magnetic intensity image (HSI) (back pocket) 3 Occurrences of greenstones, intrusions, rhyolite and trachyte in the Glenelg region (back pocket) 4 RGB radiometric image (back pocket) 5 Total count pseudocolour image (back pocket) 6 Potassium pseudocolour image (back pocket) 7 Thorium pseudocolour image (back pocket) 8 Uranium pseudocolour image (back pocket) 9 Location of VIMP airborne surveys (back pocket) 10 Major geological units (back pocket) List of Tables 1 Airborne surveys conducted over the Glenelg region 6 2 Specifications of the Glenelg and Glenelg extension airborne surveys 7 3 Summary of geophysical responses of lithological units 11 AIRBORNE SURVEY APPRAISAL - GLENELG 3 Abstract In the west, radiometric data have weak responses, compared to the south and east which is dominated by high potassium and Detailed geophysical airborne surveys were thorium responses. Drainage channels show flown in western Victoria during 1994 and 1995 high potassium, reflecting the wide distribution for the Geological Survey of Victoria, as part of of granitic intrusions in the region. Granitic the Victorian Initiative for Minerals and intrusives, volcanic extrusives, trachyte and Petroleum North West Initiative project. rhyolite vary in potassium response. High thorium responses reflects laterite that caps The magnetic data reflect a complex geological most of the land surface in the east. setting, comprising moderate to intense Quaternary Malanganee Sands show a distinct magnetic and non magnetic intrusives and low radiometric signature. extrusives, non magnetic sediments and magnetic drainage patterns and strand lines. The Glenelg region offers opportunities for the A number of these features are cut, or bound exploration of base metal, gold, diamond, by, linear magnetic, non magnetic or mineral sand and coal deposits. crosscutting trends related to the structural character of the area. The magnetic data show the dominant structural direction, in common with other parts of Victoria, to be northwest to north-northwest. Numerous lineaments and faults accompanied by dykes, reflect the strong deformation which has influenced the Glenelg region. Metasediments and sediments are typically non magnetic, and units cannot be distinguished from one another. In the southwest of the Glenelg region, multiple, moderate to intense, curvilinear, discontinuous magnetic features with a northwest trend are associated with thin belts of near surface greenstones. Significant variations in magnetic properties of granitic intrusions are apparent, and may aid in mapping and classifying these bodies. Major discrepancies between the mapped geology of the Harrow, Chetwynd River and Dergholm granites are indicated from interpreted boundaries from the magnetic data. Many intrusions display northwest, north- northwest, north-northeast, northeast and east- northeast lineations represented typically by magnetic lows. These lineations maybe be due to faults, joints or quartz veining within the intrusions. The Rocklands Rhyolite has a variable magnetic response. The magnetic data can be related to different flows. Small high frequency magnetic responses scattered throughout the Glenelg region, interpreted to be Tertiary basalts, are represented by plugs and lava flows. 4 AIRBORNE SURVEY APPRAISAL - GLENELG 1 Introduction This report presents an appraisal of new detailed airborne magnetic and radiometric data obtained over the Glenelg region (Fig. 1). It outlines the survey operations, presents preliminary results from the surveys, and provides a brief discussion of regional features identified in the new data. The Glenelg and Glenelg extension surveys (GLENELG) were flown in the Glenelg region of western Victoria during 1994 and 1995 for the Geological Survey of Victoria (GSV). These surveys were conducted as part of the Victorian Initiative for Minerals and Petroleum (VIMP). GLENELG cover parts of the Edenhope, Balmoral, Casterton and Coleraine 1:100 000 mapsheets. The surveys were flown east-west, and acquired total magnetic intensity and radiometric data. Images of the total magnetic intensity (TMI) and radiometric (RGB), total count, potassium, uranium and thorium are presented in Figures 2, 4-8. The TMI image comprises data from Glenelg and Glenelg Extension, Cavendish, Horsham and Otway Basin surveys as a composite image. Figure 3 is an interpretation of occurrences of greenstones, intrusions, rhyolite and trachyte in the Glenelg region. Potassium, thorium and uranium data are presented as K %, eTh ppm and eU ppm respectively. As a result of VIMP, the whole of the North West Initiative area has now been covered by detailed, high quality airborne surveys (Fig. 9). Geological mapping, data compilation and mineral resource assessment are also being undertaken as part of VIMP. The objective of the work in the Glenelg region is to promote mineral exploration in the region. The data from these surveys will allow for a detailed geological interpretation and assessment of the prospectivity of the area. Geophysical surveys being undertaken as part of VIMP are outlined in the Appendix. 6 AIRBORNE SURVEY APPRAISAL - GLENELG 2 Previous geophysics Two geophysical airborne surveys, flown in the 1980's by CRA Exploration (CRAE), covered parts of the Glenelg region. These surveys, Airborne surveys conducted over the Glenelg Cavendish and Horsham, collected total region are presented in Table 1. magnetic intensity and radiometric data, and were flown east-west. A 1974 regional airborne survey was flown by the Bureau of Mineral Resources (BMR, now Gravity coverage of the Glenelg region is poor, the Australian Geological Survey Organisation with 1018 gravity stations collected between - AGSO) with a line spacing of 10 kilometres 1949-1980 by the BMR. Regional gravity and an altitude of 460 m. During 1989, a surveys by the GSV collected an additional 2000 regional airborne survey was flown for the GSV gravity stations over the Edenhope and in conjunction with the BMR. This survey was Balmoral 1:100 000 mapsheets during 1995. flown east-west with a line spacing of 1500 m These data will be released in November 1995. and an altitude of 100 m. The new survey data presented here, supersede the 1974 and 1989 data in the Glenelg region. Table 1 Airborne surveys conducted over the Glenelg region GSV Survey Survey Operator Contractor Year Line Altitude Direction survey name type spacing (AGL) number 118 Horsham- TMI BMR BMR 1974 10 000 m 460 m East-west Hamilton 193 Horsham TMI/Rad CRAE Geosearch 1980/81 250 m 80 m East-west 238 Casterton TMI/Rad CRAE Austirex 1983 250 m 80 m East-west 362 Otway Basin TMI/Rad GSV/BMR Kevron 1989 1500 m 100 m East-west 363 Cavendish TMI/Rad CRAE Austirex 1989 250 m 70 m East-west 3053 Glenelg TMI/Rad GSV World 1994/95 200 m 80 m East-west Geoscience 3055 Glenelg TMI/Rad GSV World 1995 200 m 80 m East-west extension Geoscience AIRBORNE SURVEY APPRAISAL - GLENELG 7 3 Survey specifications Flight path navigation data was acquired using GPS satellite positioning. Detailed magnetic and radiometric data was The magnetic data were acquired using a split acquired for the GSV in the Glenelg region by beam Caesium Scintrex V201. The radiometric World Geoscience Corporation Ltd, using data were collected with a 33.56 litre, 256 Cessna Stationair U206G fixed wing aircraft channel spectrometer. (VH-AZG and VH-UPK). The Glenelg survey was flown during October-November 1994, and The Glenelg extension survey contains a small Glenelg extension flown in April 1995. Some hole in the data due to aviation regulations additional flying to complete the contract for prohibiting flying over the town of Coleraine. the Glenelg survey, was undertaken in July The VIMP Glenelg surveys were flown adjacent 1995.