VIMP Report 51 The geology and prospectivity of the Castlemaine, Woodend, Yea and part of Bacchus Marsh 1:100 000 map sheets J. E. Edwards, C. E. Willman, I. W. McHaffie, A. Olshina and A. J. Willocks November 1997 Bibliographic reference: EDWARDS, J.E., WILLMAN, C.E., MCHAFFIE, I.W., OLSHINA, A. and WILLOCKS, A.J., 1997. The geology and prospectivity of the Castlemaine, Woodend, Yea and part of Bacchus Marsh 1:100 000 map sheets.. Victorian Initiative for Minerals and Petroleum Report 51. Department of Natural Resources and Environment. © Crown (State of Victoria) Copyright 1997 Geological Survey of Victoria ISSN 1323 4536 ISBN 0 7306 9430 5 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 500, East Melbourne, Victoria 3065 Acknowledgements The authors wishes to thank G. Ellis for formatting the document, P. O’Shea and R. Buckley for editing the document and D. Jansen for figure formation. GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 1 Contents Abstract 3 1 Introduction 4 2 Geology 6 2.1 Geological history 7 2.2 Stratigraphy 9 Cambrian 9 Lower Ordovician 10 Upper Ordovician 12 Silurian-Devonian 12 Permian 15 Triassic 16 Tertiary 16 Quaternary 17 2.3 Intrusive rocks 17 2.4 Structure 20 Bendigo Zone 20 Melbourne Zone 21 Ballan Graben 22 3 Economic geology 23 3.1 History of mining 23 Gold 23 Other metals 31 Industrial minerals 31 3.2 Gold 33 Primary gold - general occurrence 33 Secondary (alluvial) gold deposits - general occurrence 36 Bendigo Zone 37 Melbourne Zone 41 3.3 Other metals 47 3.4 Brown coal and peat 48 3.5 Industrial minerals 49 4 Geophysics 53 4.1 Data 53 4.2 Geological features 53 5 Mineral resource potential and prospectivity 55 5.1 Gold 55 5.2 Non metallics 57 References 40 Victorian Initiative for Minerals and Petroleum (VIMP) report series 50 2 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH List of Figures 1 Location map, MELBOURNE 5 2 Geology, mineral resources and tenements, MELBOURNE (back pocket) 3 Graptolites in sediments of the Castlemaine Supergroup 11 4 Mineral resources within MELBOURNE 24 5 Primary and total goldfield production 26 6 Annual primary and alluvial goldfield production 27 7 Regional structural cross section showing structural domains 34 8 Cross section of Wattle Gully mine 39 9 TMI image showing mineral resources of MELBOURNE (back pocket) List of tables 1 Summary of granite plutons 18 2 Gold production from goldfields within MELBOURNE 25 3 Mines with production greater than 1,000 kg, Maldon Goldfield 26 4 Muckleford goldfield production 28 5 Production from major reef mines, Taradale-Malmsbury, Drummond North, lauriston goldfields 30 6 Production from major reef mines, Dayleford Goldfield 31 7 Production from major reef mines, Blackwood-Trentham Goldfield 32 8 Major gold producers within the Melbourne Zone 41 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 3 Abstract This report summarises the geology and prospectivity of the Castlemaine, Woodend, Yea and northern part of Bacchus Marsh 1:100 000 map areas (referred to in this report as MELBOURNE) in south central Victoria. New airborne geophysics conducted over MELBOURNE as part of the Victorian Initiative for Minerals and Petroleum (VIMP) has enabled a reappraisal of the regional geology and geophysics of the area. This has been complemented by a mineral resource compilation together with an appraisal of the prospectivity of the area. Gold mineralisation, both primary and secondary, represents the main exploration target in the area, and a number of styles of gold mineralisation are discussed. 4 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 1 Introduction This report summarises the geology and mineral resources of the the Castlemaine, Woodend, Yea and north part of Bacchus Marsh 1:100 000 map areas (referred to in this report as MELBOURNE) in south central Victoria (Fig. 1). This information is designed to aid mineral exploration and mineral resource development. It complements new airborne magnetic, radiometric and digital terrain data together with new gravity data. An appraisal of the airborne geophysical data from the Castlemaine-Woodend survey is given in Willocks (1997), while the Yea survey data is discussed by McDonald (1997). Detailed location, production and geological information for mines and prospects within MELBOURNE accompany this report in the MELBOURNE Mine Database. The database, explanatory notes and references are supplied on a 3.5 inch DOS disc in the following formats: MELBOURNE Mine Database Melbmine.mdb Microsoft Access 2.0 format Melbmine.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 MELBOURNE. Other themes include geology, magnetic and radiometric images, current and expired Exploration Licences (ELs), national parks and roads. This dataset is available from the Geological Survey of Victoria. GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 5 Figure 1 Location map, MELBOURNE. 6 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 2 Geology Devonian quartz sandstones and mudstones that were simply folded and faulted during the Early to Middle Devonian Tabberabberan MELBOURNE lies in the Lachlan Fold Belt, Deformation. The sedimentary pile was one of three main elements of the Tasman shortened by a minimum of 55%. Fold and Orogenic Zone which accreted to the eastern fault vergences across the Melbourne Zone margin of the Australian craton during the indicate a general model of eastward tectonic Palaeozoic. In Victoria, the Lachlan Fold Belt transport involving fold growth associated with is divided into a series of major structural thrust faults over a basal décollement surface zones, many of which are distinguished by (VandenBerg et al., 1995). The major structural different stratigraphic and tectonic histories. features of the Melbourne Zone trend north- MELBOURNE lies across the boundary of the south to northwest-southeast. Locally, Melbourne and Bendigo zones. The southern complications associated with the collisional part of the map extends across the northern tectonics have created short-lived north-south margin of the Bassian Zone which developed as compressional regimes, which have formed part of the large rift system caused by east-west trending structures in the northern lithospheric tension as Australia pulled part of the Melbourne Zone, notably in the northwards from Antarctica during the break- Dookie region. up of the Gondwana landmass (Fig. 1). The geology of MELBOURNE is presented in The eastern boundary of the Melbourne Zone Figure 2. abuts the Tabberabbera Zone along the east- dipping Governor Fault, to the east of The Bendigo Zone is a wide belt of Ordovician MELBOURNE. This fault zone is a mirror deep marine quartz-rich turbidites of the image of the Heathcote greenstone belt, Castlemaine Supergroup, which are underlain exposing Cambrian sediments and volcanics at by Cambrian marine sediments and volcanics. the surface. The Tabberabbera Zone is This zone abuts the more strongly deformed, characterised by Ordovician quartz-rich Cambro-Ordovician rocks of the Stawell Zone to turbidites and black shale overlain by Silurian the west, along the west-dipping Avoca Fault. turbidites and mudstones, and Early Devonian The Bendigo Zone is bounded to the east by the sediments. These were folded and faulted west-dipping Mount William Fault, along the during the Tabberabberan Deformation. eastern edge of the north-south trending Heathcote greenstone belt. These rocks were In the Late Devonian, the distinction between affected by Lower Silurian thin-skinned the various structural zones had disappeared deformation, correlated here with the and there followed a period of magmatic Benambran Deformation of eastern Victoria activity with intrusion of granite plutons, which (VandenBerg et al., 1992). The Cambro- in many places breached the surface to form Ordovician sequence was detached from the thick caldera volcanic sequences. These occur lower crust to form an allochthonous east- in the Bendigo, Melbourne and Tabberabbera vergent fold and thrust zone. Internal zones. In addition a thick sequence of redbeds duplexing of the Cambrian sequence occurred was deposited in the Howitt Province in the along a major mid-crustal detachment at the Melbourne and Tabberabbera zones. These base of the Ordovician (Heathcote Fault) and were folded during the Early Carboniferous within the Cambrian sequence (Mount William Kanimblan Deformation. Fault; Fergusson et al., 1986). The Cambro- Ordovician rocks were deformed into regular During the Late Devonian, the folded sediments and persistent north-trending chevron folds. were intruded and metamorphosed by granites An axial planar cleavage was strongly and in places these erupted to the surface developed in the Ordovician rocks, and weakly where they formed large calderas containing developed in the Cambrian rocks. Some of the thick pyroclastics. During the Late Silurian structures were reactivated during the