The Geology and Prospectivity of the Castlemaine, Woodend, Yea and Part of Bacchus Marsh 1:100 000 Map Sheets

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 Carboniferous and Permian, glaciers scoured Middle Devonian Tabberabberan Deformation the landscape, and glacial and fluvial sediments and were stitched by granites during the Late accumulated in glacial valleys. This appears to Devonian. have been followed by a long period of erosion. East of the Heathcote greenstone belt lies the At some time in the Mesozoic, the Gondwana Melbourne Zone. It is characterised by a supercontinent broke up and as Australia and continuous sequence of Ordovician to Middle Antarctica separated and depositional basins GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 7

formed across southern Victoria, the Palaeozoic enormous submarine fan to form a thick rocks of central Victoria were uplifted and sequence (Castlemaine Supergroup). eroded. Cycles of erosion and fluvial deposition record changes in sea level and climatic Silurian-Devonian (435–354 Ma)—formation of oscillations. Wide river valleys were incised the Melbourne 'Trough' into the highlands, and were subsequently backfilled (Calivil Formation). The Silurian and Devonian sediments of the western Melbourne Zone accumulated on the 2.1 Geological history shelf along the eastern margin of the Gondwana landmass. The deposition of The geological history of MELBOURNE can be monotonous, mud-dominated sediments was related to three main geological events: periodically interrupted by the influx of coarser grained clastic material during pulses of · the early development of the Lachlan Fold turbidite deposition. These possibly reflect Belt along the eastern margin of the uplift of the source region farther west during Gondwana landmass in the Cambrian and periods of tectonic instability, or alternatively, Ordovician. A period of submarine periods of low sea level. Only one major period volcanism and pelagic sedimentation in an of marine transgression is recorded in the intra-oceanic island arc–back-arc basin sedimentary sequence. system was followed by the deposition of a Llandovery (Benambran Orogeny) to early thick sequence of continentally derived Ludlow (435–420 Ma) sediments by turbidity currents;

The Benambran Orogeny, in the Early Silurian, · the development and subsequent infilling was an event in which the Ordovician and and folding of the Melbourne 'Trough' Cambrian sediments in western Victoria were adjacent to the eastern Gondwana shore in folded, and substantially shortened and the Silurian to Middle Devonian. Deposition thickened, and were accreted onto the of this sedimentary sequence was influenced Gondwana margin. by periods of tectonic activity, changes in the sediment source and supply, and eustatic At about the Ordovician-Silurian boundary, a changes in sea level; and change in global eustatic or climatic conditions

resulted in a major change in the submarine · the formation of the Ballan Graben and the environment. The anoxic waters into which the adjacent Central Victorian Highlands caused shales and thin-bedded turbidites of the Late by the separation of Australia and Ordovician were deposited became oxygenated, Antarctica during the break-up of the and there was an influx of bottom fauna into Gondwana supercontinent in the Late the marine system. The mud-dominated Jurassic to Pliocene. This geological event sediments deposited at this time are intensely can be divided into several major periods of bioturbated (Costerfield and Deep Creek deposition which are related to discrete siltstones). periods of uplift and erosion. Newly uplifted rocks along the margins of the Cambrian-Ordovician (570–435 Ma)—early craton provided a source of sediments, which development of the Lachlan Fold Belt were deposited by turbidity currents across the Melbourne Zone (Springfield Sandstone, During the Early Cambrian an ocean floor Wapentake Formation, Anderson Creek developed along the eastern margin of the Formation). As the sediment supply waned, Precambrian Gondwana craton, and submarine conditions of predominantly hemipelagic mud volcanic rocks and pelagic sediments were deposition returned to the shelf (Dargile deposited in intra-oceanic island arc and Formation, Kilmore Siltstone, Melbourne backarc basin environments (Heathcote Formation). greenstones). During the Ordovician, these were covered by an extensive sheet of turbidites Late Ludlow to early Pragian (420–402 Ma) eroded from the Delamerian mountain chain in western Victorian and South Australia. These Deposition of mud-dominated sediments sediments were transported across the shelf continued across much of the Melbourne Zone and into deep water by turbidity currents in an (Dargile Formation and Humevale Formation), but near-shore shallow water deposits 8 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

accumulated along the shoreline which After the Tabberrabberan Deformation, the gradually migrated to the east (McIvor volcanic and sedimentary sequence was Sandstone and Mount Ida Formation). In the intruded and metamorphosed by granites and western part of the basin, there was a sudden subjected to prolonged erosion. Elsewhere in influx of coarse-grained clastic material during central Victoria the products of this erosion the Late Ludlow (Broadford Formation). This were deposited as thick redbeds and felsic sediment was transported by turbidity currents volcanics (Avon and Mansfield groups) but which carved large submarine channels these are not preserved this far west. through the mud-dominated shelf sediments. As the sediment supply waned, the finer In the Late Carboniferous and Permian, grained and more thinly bedded Puckapunyal Gondwana experienced a prolonged ice age. and Waranga Formation sediments were The effects of climatic and eustatic oscillations deposited to the north. during this period are shown by scattered marine sediments, and tillite and striated Early Pragian to Middle Devonian (402–370 pavements made by glaciers as they scoured Ma) across the landscape (Wild Duck and Urana formations). Widespread subsidence and a eustatic rise in sea level dramatically altered the depositional Triassic to Late Cretaceous (250–65 Ma)— style in the Melbourne Zone to one of continued erosion and breakup of the Gondwana pelagic sedimentation in deep, anoxic water supercontinent across the entire basin (Wilson Creek Shale). As the sea level then fell, the re-emergence of A long period of erosion followed the Permian, the basin margins provided a new source of during which most of the Permian deposits sediment into the basin. Initial rapid erosion of were removed. Between the Late Jurassic and these soft sediments provided material for the the Late Cretaceous a large rift basin formed Norton Gully Sandstone, but as the rate of across the Gondwana landmass, where the erosion subsided, the style changed to finer southern margin of Victoria now lies, due to grained and more thinly bedded (Montys Hut lithospheric tension as Australia pulled Formation). These Walhalla Group sediments northwards from Antarctica. Large-scale are the final filling of the marine basin, and the subsidence along the rift was accompanied by overlying Cathedral Group sediments to the significant passive margin uplift of the east show a change to fluvial conditions. Palaeozoic rocks along the northern margin of the rift, which formed the Victorian Highlands. Middle Devonian–Permian (370–250 Ma)— deformation, granite intrusion, and frostbite The uplift of Palaeozoic rocks occurred during a climate of high rainfall, and was accompanied Following the retreat of the sea from the land, by rapid erosion. As relief across the northern HEATHCOTE was affected by the Middle margin of the rift valley increased, rapid and Devonian Tabberabberan Deformation. The extensive erosion and incision occurred and a previously undeformed sediments of the very thick sequence of fluvial sediments was Melbourne Zone were faulted and folded into deposited in the Bassian Rift. broad north-south trending regional anticlinoria and synclinoria. Transpressional Along the northern flanks of the Palaeozoic shortening between the Melbourne Zone and divide the relief was less and the rate of erosion the eastern Victorian block gave rise to east- less rapid. Equivalent deposits are not west trending folds in the north of the preserved as they were probably eroded and Melbourne Zone and warped the earlier-formed reworked during successive periods of uplift. north-south folds to give them doubly plunging, curvilinear axial traces. The regional effect of Palaeocene to middle Eocene (65–45 Ma) this is a structural interference pattern of basin and domes. Major thrusts in the Bendigo- The Murray Basin was created to the north of Ballarat Zone were reactivated, and thrusting the Palaeozoic divide, during a period of along the Mount William Fault placed widespread uplift which began at 65 Ma. The Cambrian and Ordovician sediments onto earliest sedimentation in this newly formed folded Silurian-Devonian sediments of the basin was fluvial (Warina Formation at the Melbourne Zone. base of the Renmark Group). In the southern hinterland, broad, deep valleys were incised GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 9

into the Central Victorian Highlands, and the continued into the Quaternary. Large colluvial and fluvial sediments of the White outpourings of basalt covered the northern Hills Gravel were deposited. fringe of the Bassian Zone, mainly as valley flows. Middle Eocene to middle Miocene (45–15 Ma)- development of the circum-Antarctic current Pliocene to Recent (5 Ma to present)

At about 45 Ma, the rate of sea floor spreading As the Murray Basin filled with sediment, and between Australia and Antarctica increased, the valleys extending into the Central Victorian and the seaway between the two landmasses Highlands were being back-filled, the relief of widened. The development of the circum- the land was gradually reduced and erosion Antarctic current was accompanied by a change rates slowed. Fluvial processes changed from to a warmer climate with a significantly lower drainage in discrete channels, to a series of rainfall, and a period of transgression. The anastomosing and interweaving braided and fine-grained marginal marine sediments of the meandering streams that flowed north from the Nirranda Group in the Otway Basin, and the Central Victorian Highlands. These rivers well sorted, distal deposits of the Olney carried the sediments of the Shepparton Formation in the Murray Basin indicate that Formation, which were deposited to form the this period of deposition was not accompanied flat Riverine Plain. by the rapid and high energy erosion which characterised the earlier accumulation of the 2.2 Stratigraphy White Hills Gravel. Cambrian There was a retreat of the sea during the mid- Oligocene, but a major marine transgression Cambrian rocks probably underlie much of the began in the late Oligocene (29 Ma) and marks Palaeozoic sedimentary sequence of central a dramatic change in the style of sedimentation Victoria, but in MELBOURNE, these rocks are in the Otway and Murray basins. exposed at the surface only in the footwall of Sedimentation in the Otway Basin was the Mount William Fault. Here they form part characterised by biological calcium carbonate, of the southern segment of the narrow, north- mostly by bryozoa, in the recently developed south trending Heathcote greenstone belt, and open-marine circulation conditions. The sea in MELBOURNE are exposed at the surface entered the Murray Basin, forming the only between Tooborac and Heathcote, and from true widespread marine environment in the Mount William to Bolinda. eastern portion of the basin, and the marine sediments of the Murray Group were deposited. Recent mapping of the Heathcote greenstone belt to the north of the Cobaw Batholith has Along the southern margin of the Murray Basin enabled the nomenclature of these Cambrian drainage systems were re-established as narrow rocks to be rationalised and formalised. The valleys in the Palaeocene–Eocene palaeovalleys names Mount William metabasalt and of the White Hills Gravel. Material reworked Monegeetta Shale were used locally from the White Hills Gravel was deposited, (VandenBerg, 1992) to refer to what are now together with minor newly eroded material, as the Burramboot and Knowsley East formations the Calivil Formation in these valleys. respectively. The Goldie Chert retains its Middle Miocene to Pliocene (15–5 Ma)—final name. The following descriptions are modified retreat of the sea and basaltic volcanism from VandenBerg (1992) and Edwards et al. (in prep.). Regional uplift had ceased by the early Pliocene, and the sea had retreated from the onshore region. In the Murray Basin this retreat is marked by the interfingering of the shallow marine and littoral Parilla Sand with the fluvial Calivil Formation. The retreat was interrupted by several minor transgressions, which raised stream base levels and facilitated the periodic back-filling of valleys by the Calivil Formation. A major period of widespread volcanism in Victoria began in the Pliocene and 10 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Burramboot Formation: Ev (Edwards et al., in 045-678). The chert overlies the Monegeetta prep.) Shale with a gradational contact, and underlies the Ordovician Romsey Group with a sharp but Cambrian volcanic rocks occur along the entire conformable contact. It ranges from 190 m Heathcote greenstone belt in MELBOURNE, thick at Deep Creek near Monegeetta, to 290 m but are only well-exposed in Deep Creek below near View Hill. Brock's Hill. These rocks belong to the Burramboot Formation. They underlie the The basal 50 m consisting of chert is mostly Knowsley East Formation with a sharp, thin-bedded but occasionally very finely concordant and possibly conformable contact, banded, or structureless, and passes gradually while the lower contact is faulted by the Mount up into a siliceous shale of similar appearance. William Fault. Their maximum exposed thickness is approximately 1600 m. The chert is thought to be largely derived from radiolaria, although recrystallisation has The formation in MELBOURNE consists of destroyed any evidence of this. Conodonts altered tholeiitic basalt flows and interbedded suggest an age from latest Cambrian to earliest bands of black shale, siliceous shale, Ordovician. volcanogenic fine conglomerate, sandstone and siltstone, and some shale breccia. Lower Ordovician

Crawford et al. (1984) infer the basalts to have Ordovician sediments form the bedrock for most been extruded in a back-arc basin setting, of the area west of the Heathcote Fault Zone in behind an arc located to the east. the Bendigo Zone. The Melbourne Zone contains only a small area of Ordovician Knowsley East Formation (Monegeetta Shale): sedimentary rocks in the Darraweit Guim area. Emk (Edwards et al., in prep.) Castlemaine Supergroup (Olh, Olb, Oll, Oly, The Knowsley East Formation extends along Ola, Olm, Olr, Ol; Cas & VandenBerg, 1988) the entire Heathcote greenstone belt in MELBOURNE, but is best exposed in Deep The Castlemaine Supergroup is a thick Creek to the east of Portingales Road. It sequence of marine quartz-rich sandstone to overlies the Burramboot Formation with a granulestone turbidites, interbedded with black sharp, concordant and probably conformable to grey graptolitic shale and mudstone. The contact. The measured thickness of the unit supergroup occurs only west of the Mount ranges from about 200 m to at least 580 m at William Fault zone in the Bendigo zone and has Kilmore Gap. a total thickness in the order of 2-3 km (VandenBerg & Stewart, 1992). The sequence is very uniform The formation is composed predominantly of and well-bedded with bed thicknesses usually black shale and siltstone, and minor less than 2 m and averaging less than 1 m. interbedded graded lithic sandstone and Packages of sandstone-rich turbidites siltstone. Several thin beds of reworked commonly occur up to about 30 m thick volcanic detritus occur in the top 20 m of the sometimes interbedded with shale-rich unit. packages. The sandstone beds are laterally discontinuous, apparently due to the Most of the formation accumulated as a thick channellised origin of amalgamated sandstone deposit of hemipelagic mud with minor and thick-bedded sandstone facies. deposition from turbidity currents and gravity Lithostratigraphic units are difficult to slumps. It is considered to be Middle Cambrian recognise but detailed biostratigraphic zonation in age, but the fossil evidence for this needs using graptolites is an important mapping tool revision. (Fig. 3). The only lithological subdivision recognised so far is in the Romsey-Lancefield Goldie Chert: Eug (Thomas, 1960) area where the lower part of the supergroup has been divided into the Romsey Group Goldie Chert is discontinuously exposed along underlying undifferentiated Castlemaine the western margin of the Heathcote Supergroup. greenstone belt, and is well exposed at the type section in a gravel quarry at View Hill (AMG GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 11

Figure 3 Graptolites in sediments of the Castlemaine Supergroup at Willeys quarry, Macedon: Goniograptus speciosus (large specimen), a: Dichograptus sp., b: Didymograptus (Corymbograptus) v-deflexus, c: Oncograptus upsilon, d: Cardiograptus morsus, e: Isograptus caduceus australis, f: Pseudisograptus manubriatus, g: Pseudotrigonograptus ensiformis. 12 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

The Romsey Group occurs along a narrow north-south trending belt about 15 km long, Silurian-Devonian immediately west of the Heathcote greenstone belt and south of the Cobaw Batholith. The The Silurian and Devonian geology shown on group consists of about 1200 m of marine the map is in need of revision. A lack of quartz-mica turbidite and siltstone units detailed mapping of these poorly exposed alternating with units of black shale and is sediments and their subtle lithological changes, distinguished from the rest of the Castlemaine in conjunction with a lack of well-described Supergroup by the presence of thin beds of indicator fossils, mean that the stratigraphic cherty shale. VandenBerg (1992) found it to be relationships of the units are poorly understood. conformable with the underlying Cambrian In addition the inconsistent use of existing sediments. nomenclature and the introduction of poorly defined new names has led to much confusion Upper Ordovician in the literature.

The distribution of the Upper Ordovician is Deep Creek Siltstone: Sld (Thomas, 1956, quite different to the Lower Ordovician. It 1960) occurs mainly in the area east of the Djerriwarrh Fault along which it is juxtaposed The Deep Creek Siltstone is exposed in the against strongly cleaved Castlemaine Deep Creek valley west of Darraweit Guim and Supergroup. The Upper Ordovician is divided south to Bulla, in the Boyds Creek valley north into three formations: Riddell Sandstone, of Darraweit Guim, and in Jacksons Creek Darraweit Guim Mudstone and the Bolinda immediately downstream from the Organ Pipes Shale. The Riddell Sandstone is probably National Park. It is the earliest Silurian mostly within the Melbourne Zone but the sediment exposed in the Melbourne Zone. formation appears to straddle the inferred southern continuation of the Heathcote The siltstone is conformably overlain by the Greenstone Belt in an area where most of the Springfield Sandstone and is marked by the geological relationships are hidden by Newer appearance of thick-bedded sandstone of Volcanics. `proximal' turbidite type. Its boundary with the underlying Darraweit Guim Mudstone is not Riddell Sandstone: Our (VandenBerg, 1992) well exposed.

The Riddell Sandstone consists of interbedded The Formation consists dominantly of grey marine turbiditic sandstone, siltstone, black siltstone, and has a total thickness of between shale and rare fine conglomerate and very 800–1000 m (VandenBerg, 1992). Fossil fauna coarse sandstone. Previously referred to as the indicate that deposition of this unit occurred Riddell Grits, the very coarse sandstones in this during the Llandovery (VandenBerg, 1992). formation are now interpreted as mass flow turbidites. The Riddell Sandstone extends Springfield Sandstone Sls (Thomas, 1956, westward to the Djerriwarrh Fault where it is 1960) and faulted against strongly deformed Castlemaine Chintin Formation Sls (Thomas, 1956, 1960; Supergroup. Slc)

Bolinda Shale: Oub (VandenBerg, 1984) The Springfield Sandstone extends along Deep Creek and the Maribyrnong River from The Bolinda Shale consists of about 500 m of Willowmavin to Keilor. It also outcrops in interbedded marine thin-bedded dark grey Jackson's Creek east of the Organ Pipes shale, dark and pale massive siltstone and pale National Park. The Chintin Formation is grey sandstone. recognised only in the Willowmavin district, where it has the same distribution as the Darraweit Guim Mudstone: Oub (VandenBerg, Springfield Sandstone. 1984) The Springfield Sandstone conformably overlies This thin (20-45 m) but distinctive formation Deep Creek Siltstone. It is conformably consists of marine medium to thick bedded overlain by the Chintin Formation, which in massive calcareous mudstone. The mudstone turn has a conformable and lithologically contains shelly fossils and is black when fresh. gradational contact with the overlying Kilmore GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 13

Siltstone. The two formations are lateral Llandovery to early Wenlock (VandenBerg, equivalents of the Wapentake Formation to the 1992). north. The Springfield Sandstone attains a thickness of 980 m on the eastern flank of the Kilmore Siltstone: Suk (VandenBerg, 1992) Darraweit Guim Anticlinorium. The thickness Dargile Formation: Sud (Thomas, 1937) of the Chintin Formation is rather variable, Melbourne Formation: Sum (VandenBerg, from about 170 m in Slab Hut Creek, to as little 1988) as 75 m in the western limb of the Clunie Syncline. On the map, the Kilmore Siltstone occurs to the east of Kilmore between Wallan and Glenoura, The Springfield Sandstone is characterised by and in the core of the Clunie Syncline south of medium- to thick-bedded turbidite sandstone the Cobaw Batholith. The Dargile Formation is interbedded with siltstone, which alternate exposed to the east of the Northern Highway with intervals of siltstone and shaly siltstone near Tooborac, and in major fold hinges to the and thin-bedded sandstone. The Chintin east of Upper Plenty. Melbourne Formation Formation consists mainly of dark grey to sediments are restricted to the core of the green, massive to laminated, very poorly sorted Limestone Creek Anticline at Yea. The sandy coarse siltstone to silty sandstone. boundary relationships between these units are mostly poorly understood and unmapped. It is The Springfield Sandstone was deposited in a probably that these three units form lateral turbidite fan setting which incorporated equivalents of parts, or all of each other, but, submarine valleys, and inter-channel 'highs'. given the current poor understanding of such The Chintin Formation represents an episode of relationships, these lithologically similar units large-scale slumping where originally shallow- are here described together. water shelf sediments were slumped into deeper water. The age of these two formations All of the units probably have conformable and is estimated to be either very late Llandovery or lithologically gradational contacts with early Wenlock. underlying and overlying formations. The thickness of these formations cannot be Wapentake Formation: Slp (Thomas, 1937) estimated until their boundaries are better defined. The formation is restricted to northern MELBOURNE, and is shown on the map as a The dominant lithology of these formations is small exposure about 8 km northwest of thin-bedded siltstone and very thin-bedded Tooborac. Recent mapping indicates that the sandstone. They represent a period of rapid formation probably extends further to the deposition in a tectonically stable, shelf-like south. It is particularly well exposed in new environment. The age range of this very thick road cuttings along the Tooborac-Seymour group of sediments is expected to be quite large. Road, and these provide an excellent type locality (AMG 312200-5900450; Edwards et al., McIvor Sandstone: Sui (Thomas, 1937; in prep.). The unit has a lithologically VandenBerg et al., 1976) gradational contact with the underlying Costerfield Siltstone (not exposed in McIvor Sandstone is restricted to two small MELBOURNE), and conformably underlies the outcrops east of the Mount William Fault at Dargile Formation. It is laterally equivalent to Tooborac. The formation passes conformably the Springfield Sandstone and overlying into the underlying Dargile Formation and the Chintin Formation near Kilmore (VandenBerg, overlying Mount Ida Formation. It probably 1992), and has an estimated thickness of 1500– grades laterally into the Broadford Formation 1750 m. to the east, and is laterally equivalent to the lower part of the Humevale Siltstone to the The formation is a single, coarsening upward south. The sandstone is approximately 1900 m sequence of turbiditic sandstone and thick to the north, but is considerably thinner interbedded siltstone. It was deposited by here. turbidity currents into the relatively quiet deep water of a shelf environment below fair- The formation is a hard, pale grey quartzite, weather wave base. The fossil fauna of which weathers to a white-grey sugary textured laterally equivalent sediments at Kilmore rock. It was deposited in a high energy, shallow indicate that it probably spans the late water environment, and spans the late Ludlow 14 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

and Pridoli series of the Late Silurian Siltstone. The nature of its boundary with the (VandenBerg, 1988). overlying Walhalla Group here is unknown. It is probably less than 500 m thick. Broadford Formation: Dlb Undifferentiated Devonian sediments: Dl The Wilson Creek Shale is typically a dark grey to black paper-laminated shale, which is mostly Broadford Formation sediments are shown on bleached to pale-grey, buff and pink colours. It the map to extend from the Moormbool Fault to was deposited in a relatively deep and anoxic, Hilldene, however, recent mapping here quiet water environment, into which indicates that these rocks belong to the progressively stronger turbidity currents Humevale Siltstone (Edwards et al., in prep.). carried and deposited sediment. Recent conodont work on laterally equivalent units Previous maps show the Broadford Formation indicates that the formation has a mid-Pragian extending along the axis of the major synclines to Emsian age (Mawson & Talent, 1994). at, and to the east of Broadford. These rocks are shown on the map as undifferentiated Walhalla Group Devonian sediments, and further work is required to determine to which formation they Norton Gully Sandstone: Dlwn (Thomas, 1953; belong. VandenBerg, 1975)

Humevale Siltstone: Dlh (Williams, 1964) The Norton Gully Sandstone has been mapped to the north of the Trawool Granite, but The Humevale Siltstone is shown on the map to probably also occurs in unmapped areas to the incorporate the bulk of the gently folded rocks south where it is presently incorporated into to the east of Kilmore. Early descriptions of the the Humevale Siltstone. The Norton Gully unit show it to be lithologically highly variable Sandstone probably has a lithologically (Williams, 1964). Recent mapping shows that gradational and conformable contact with the the upper parts of the unit belong to the Wilson underlying Wilson Creek Shale, and the Creek Shale, Norton Gully Sandstone and overlying Montys Hut Formation. The Montys Hut formations, and that the basal thickness of the formation is unknown. sediments are probably part of the underlying Dargile Formation (Edwards et al., in prep.). The Norton Gully Sandstone is lithologically variable, with sandstone dominated packages The Humevale Siltstone has conformable interbedded with paper shales like the Wilson boundaries with the underlying Dargile Creek Shale and laminated shales like the Formation (and Dargile Formation equivalents) Montys Hut Formation. and the overlying Wilson Creek Shale (where this has been recognised). Stratigraphic The shales and laminated siltstones represent a relationships indicate that it is equivalent to relatively deep water environment, which has the McIvor Sandstone and Mount Ida periodically experienced higher energy formations to the west. conditions with deposition of the sandstones and conglomerates from high concentration The formation consists mainly of thinly bedded turbidity currents or debris flows. The (<1 cm) mudstone and siltstone. It represents formation is interpreted as Emsian, and quiet water deposition throughout the Pridoli possibly lower Eifelian, or upper Early and Lochkovian, and possibly into the very Devonian to Middle Devonian in age early Pragian. (VandenBerg, 1988).

Wilson Creek Shale: SDjg (Thomas, 1953; Montys Hut Formation: Dlwm (VandenBerg, VandenBerg, 1975) 1975).

The Wilson Creek Shale is shown on the map to The Montys Hut Formation outcrops against outcrop in the Seymour district, north of the the western margin of the Strathbogie Granite, Trawool Granite. The formation also occurs to but also occurs in unmapped areas to the south the south of the granite, in the unmapped areas where it is presently incorporated into the presently marked as Humevale Siltstone. The Humevale Siltstone. The formation passes shale probably passes conformably and conformably into the underlying Norton Gully gradationally into the underlying Humevale Sandstone. The nature of the upper boundary GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 15

and thickness of the unit in this region is Hesket Ignimbrite: Dvm1 (VandenBerg, in unknown. prep.)

Siltstone is the predominant lithology, but in The Hesket Ignimbrite is exposed only at the places it is rhythmically interbedded with very northeastern rim of the caldera, near Hesket. fine- to fine-grained sandstone. The siltstone It forms a thin unit which may be composed of accumulated in a quiet water environment, several ignimbrite flows. None of the contacts while the coarser grained beds are the result of with surrounding units are exposed. The reworking by bottom currents, and deposition exposed thickness of the ignimbrite is about 50 from weak, distal parts of low density currents m, but as the boundary contacts may be faulted, which disrupted the background accumulation and as the unit is likely to dip and thicken of silt. With consideration to the age of the towards the centre of the caldera, it is probably underlying Norton Gully Sandstone, it is substantially thicker than this. probably Middle Devonian. The Hesket Ignimbrite is a dark grey and fine- Kerrie Conglomerate: SDk (Skeats & grained porphyritic rock with a glassy Summers, 1912) groundmass.

Kerrie Conglomerate occupies a single major Willimigongong Ignimbrite: Dvm2 (Gregory, synclinal structure between Riddells Creek 1902; Summers, 1914) west of Riddell, and the Black Range north of Kerrie, where it outcrops around the The Willimigongong Ignimbrite incorporates southeastern and eastern fringe of the Macedon the main sequence of hypersthene ignimbrites Ranges. It overlies Ordovician Riddell filling the Macedon Caldera just east of the Sandstone with a marked angular Woodend township. The contact with unconformity, and is intruded and surrounding Ordovician sediments is not metamorphosed by the Barringo Granodiorite. exposed and is inferred to be a caldera margin The maximum preserved thickness is about 900 ring fault. The exposed thickness of the unit is m in the Black Range, but the sequence here is at least 400 m. incomplete. This unit is a dark grey, medium-grained, The formation consists of two main lithologies: hypersthene-feldspar ignimbrite with a very conglomerate, which forms the bulk of the high phenocryst content. formation, and sandstone with interbedded siltstone. The very homogeneous nature of the Permian conglomerate and the general lack of bedding indicate deposition in a braided stream. It was Permian fluvioglacial sediments occur in deposited at some time between the end of the scattered outcrops in the southwestern part of Ordovician and the Late Devonian, but there is MELBOURNE. The majority of the deposits no reliable evidence to constrain the age of the are in the Bacchus Marsh–Coimadai area (Wild unit within this large time span. Duck Formation), where they are preserved in a series of downfaulted blocks between a set of Mount Macedon Igneous Complex WNW trending normal faults. Near Lauriston, west of Kyneton, Permian sandstone occurs in The Macedon Volcanic Complex at Woodend the valleys and continues under the newer consists of the small Macedon Caldera, filled Volcanics. Some of this sandstone has been mostly with a single unit of rhyodacite quarried for building stone. ignimbrite, flanked to the east by the Barringo Granodiorite which forms a small subvolcanic pluton. There is a single small outcrop of granite porphyry, inferred to be part of a ring dyke. The following descriptions are taken from unpublished work by VandenBerg (in prep).

The volcanics consist of two units: the pre- collapse Hesket Ignimbrite, and the collapse phase Willimigongong Ignimbrite. 16 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Wild Duck Formation: P (Dunn, 1890) distinct petrographic groups consisting of firstly, a silica undersaturated group of olivine The Wild Duck Formation includes all the nephelinites, olivine anacimites and basanites, Permian rocks of glacial, glaciofluvial, and secondly, a nearly silica saturated group of glaciolacustrine and marine origin in the alkali olivine basalts. Individual flows are Bacchus Marsh area (Roberts, 1984). The mostly less than 5 m thick but the total formation consists of diamictite, sandstone, thickness may exceed 200 m. The age of the mudstone and conglomerate. The diamictites Pentland Hills Volcanics is known from three are interpreted either as mostly tillites (Bowen, K/Ar dates of 53.4±0.9 Ma, 62.7±1.4 Ma and 1959) or a combination of tillites and 60.4±2.0 Ma (Wellman, 1974). The volcanics redeposited tillites (Crowell & Frakes, 1971). A are associated with numerous basic and minor occurrence of a marine conglomerate is ultrabasic dykes which intrude the Castlemaine described by Garratt (1969). The thickness of Supergroup along WNW trending normal the Wild Duck Formation reaches a maximum faults. of 1100 m in Korkuperrimul Creek. The beds generally dip from 10–30° to the south and Pintadeen Basalt: Tmv (VandenBerg, 1992) overlie the Castlemaine Supergroup with an angular unconformity. The Pintadeen Basalt is part of a group of Miocene age basaltic volcanics which were Triassic extruded some 20 Ma after the Older Volcanics and about 16 Ma before the Newer Volcanics. Council Trench Formation: Trc (Roberts, 1984) The early Miocene Pintadeen Basalt occurs as This formation consists of sandstone and small hilltop cappings east of Kilmore and has a conglomerate in a small and isolated outcrop K/Ar date of 22.5±0.1 Ma (McKenzie et al., 3 km northwest of Bacchus Marsh (Roberts, 1984; VandenBerg, 1992). The basalt is up to 65 1984). They contain a poor flora of plant m thick and compositionally is classed as an remains. The sediments overlie thin Permian olivine basalt. marine mudstone and massive sandstone (Bowen & Thomas, 1988). Werribee Formation: Tew (Thomas & Baragwanath, 1950) Tertiary The Werribee Formation is exposed to the east Tertiary age rocks occur as isolated outcrops of and south of Ballan in the catchment regions of basalt or fluviatile sediments in the area of the Parwan River, mainly on the western MELBOURNE covered by this report. Volcanic upthrown regions of the Rowsley Fault. It has rocks were extruded in response to extensional a total thickness of up to 275 m in the Ballan tectonics associated with the break-up of Graben. It extends suburface to the south and Australia and Antarctica and subsequent sea- southwest where it is probably the lateral floor spreading (Price et al., 1988). The equivalent of the Eastern View Formation, and volcanics are mainly divided into two periods to the east of the Rowsley Fault to Melbourne. recognised by their petrology and physiographic It is overlain by the Fyansford Formation, setting. The Older Volcanics are Late Jurassic mainly conformably, but also disconformably to Miocene in age and the Newer Volcanics are due to brief time intervals of non-deposition, mainly Pliocene to Holocene. On and by Newer Volcanic lava flows on the MELBOURNE the Older Volcanics are Werribee plain. restricted to the Eocene and Oligocene. The only exception to this broad subdivision is the The formation generally consists of fine- to Pintadeen Basalt east of Kilmore. The total coarse-grained quartz sand with minor gravel outcrop area of Tertiary sediments is small but layers, interbedded carbonaceous silt and clay they are probably more extensive in the bands and brown coal seams, and minor subsurface occurring beneath Newer Volcanics dolomite and dolomitic sands. lava flows. Two coal seams have been defined and include Older Volcanics: Tvo the Altona coal subsurface deposit in the vicinity of Altona, Werribee and Newport The Older Volcanics occur in the Ballan Graben (Herman, 1922), and the Maddingley Seam where they are referred to as the Pentland Hills (Edwards, 1950) at Bacchus Marsh, although Volcanics (Roberts, 1984). These form two drilling results indicate that these are probably GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 17

laterally continuous (Roberts, 1984; Brewster, along the eastern, downthrown, margin of the 1988). The seams reach thickness of at least Rowsley Fault. 50 m at Bacchus Marsh, but the seam rapidly thins and splits and grades laterally into The sediments are lithologically highly ligneous clays, clay and sand. At Maddingley variable, as they comprise a great variety of the coal is a dark brown earthy variety of sediments which strongly reflect the lithologies lignite with areas of abundant plant remains of their source. Deposits in the Kilmore district and woody material, and is locally pyritic and are described by VandenBerg (1992). clayey. The calorific value (dry basis) is similar to that of the Latrobe Valley. Newer Volcanics: Qvt, Qvn, Qvs

The Werribee Formation is a non-marine upper Newer Volcanics cover a large area of delta plain and floodplain deposit. Coal and MELBOURNE and can be divided into two carbonaceous clay bands, and dolomitic main phases: an early (Late Miocene to sediments were deposited in swamp and Pliocene) phase and a late (Pleistocene) phase freshwater lake environments. It is regarded (VandenBerg, 1992). In the goldfields areas of as Palaeocene to Lower Miocene in age, based Castlemaine, Guildford and Daylesford, flow on fossil flora in coal seams (Partridge, 1971). remnants occur as isolated hill cappings. Elsewhere, the lavas form extensive plains Brighton Group occasionally interrupted by scoria cones. There are two main compositional groups: an alkaline Moorabool Viaduct Sand/Hanson Plain Sand: series (Qvt) consisting of trachyte, mugearite, Tpb (Gill, 1950) hawaiite, benmoreite and a second group of Undifferentiated sand: Tp tholeiitic to alkaline basalts (Qvn).

The Brighton Group is restricted to south of the Quaternary Great Divide, and here incorporates the Pliocene-Miocene fluvial gravels and sands, Quaternary sediments: Qs, Qpc, Qpa, Qrt, which are locally subdivided into numerous Qrm, Qrc, Qra formation names. The group occurs as small outcrops scattered across the map, but is For the area of MELBOURNE covered by this concentrated in the Bullengarook, West Melton report, the Quaternary period has been one and Ballan districts. The formation mainly dominated firstly by volcanic activity (see overlies Ordovician and Permian sediments Newer Volcanics above) followed by deposition with a low angular unconformity, and is of alluvium in the present drainage system. disconformably overlain by Newer Volcanic lava Other minor deposits include colluvium, flows and younger fluvial sediments. In the hillwash, and swamp deposits. Bacchus Marsh area Roberts (1984) found some of these sediments interfinger with Newer 2.3 Intrusive rocks Volcanic lava flows. Granites occur across the whole of The group is extremely lithologically variable, MELBOURNE. Not all of these have been and includes ferruginous sand and gravel studied in any detail, so the petrographic deposits, fine- to coarse-grained white sands character and mineral composition are not and gravels, and clayey sands. known for all of the plutons. Plutons which Post Newer Volcanic sediments: Tpe, Tpo share distinct textural, and geochemical and mineralogical characteristics have been grouped into suites (Chappell et al., 1991; This unit consists of extensive and very thin Table 1). Several plutons have had their age sheets of sand and gravel which either overlie determined by radiometric means. The or occur around the margins of the Newer available age determinations and stratigraphic Volcanics, and whose deposition has been a relationships indicate that the plutons here response to drainage modifications by either intruded during the late Middle Devonian to Newer Volcanic lava flows or faults. They are Late Devonian. Table 1 lists the plutons and most extensively formed in the Macedon district gives brief details about their geochemical between Riddells Creek and Lancefield, and characteristics and their measured age. 18 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Table 1 Summary of granite plutons

G No. Name Suite1 Type2 Age Reference K/Ar Rb/Sr

217 Strathbogie Granite Ra S,F,f 362±4 365 Baker, 1940 218 Trawool Granite Ra S - 362 McInerny, 1929 219 King Parrot Creek Ra S,F,u - 370 Gray, 1990 Granodiorite 220 Flowerdale Granodiorite Un - - - Williams, 1964 221 Mount Disappointment Ab I,M,u 370 Tattam, 1925; Williams, 1964; Granodiorite Gray, 1990 222 Glenvale Granodiorite Un - - - Chappell et al., 1991 223 Black Range Granodiorite Un S - - Hills, 1959; McLaughlin, 1976; VandenBerg, 1977 279 Ingliston Granite Rc I,M,u - - Beavis, 1967 280 Mount Egerton Granite Mf I,F,u - - White & Chappell, 1988 282 Barringo Granodiorite Ab I,M,u - - Tattam, 1925; VandenBerg (in prep.) 283 Pyalong Granite Py S,F,u - 366 Gray, 1990 284 Baynton Adamellite Rc I,F,u 282±1 365 Stewart, 1966; Gray, 1990 5 285 Beauvallet Granodiorite Rc I,F,u - Hills, 1959; 359±7; VandenBerg (in prep.) 363±7 287 Glenaroua Granite Py S,F,u - - Stewart, 1966 290 Harcourt Granodiorite Rc I,M,u - 375; Tattam, 1925; 368 Gray, 1990

LEGEND 1 Suite (Chappell et al., 1991): Ab=Barringo, Rc=Harcourt, Mf=Mount Egerton, Py=Pyalong, Ra=Strathbogie, Un=Unassigned 2 Type: S=S-type, I=I-type, M=Mafic (<70% silica), F=Felsic (>70% silica), f=fractionated, u=unfractionated

Strathbogie Batholith: G217, G218, G219 G218 Trawool Granite: occurs as a lobe which The Strathbogie Batholith is subdivided into extends from the southwest edge of the the Strathbogie and Trawool plutons in Strathbogie Granite. It is a grey, fine-grained northeastern MELBOURNE. These S-type, granite which is occasionally porphyritic, and non-magnetic bodies form tor-covered hills contains accessory biotite, apatite and zircon. It surrounded by prominent metamorphic is magnetically and radiometrically aureoles. indistinguishable from the main Strathbogie Granite, and the mapped boundary between the G217 Strathbogie Granite: forms a very large two is essentially an arbitrary one. pluton¾only a small portion of which lies in the map area. Much of the pluton coincides with a G219 King Parrot Creek Granite: forms a larger magnetic high with a very diffuse small elongate outcrop of coarse-grained, boundary, whose shape bears little resemblance biotite-bearing granite, which extends from the to the boundaries of the granite in outcrop. The southern boundary of the Trawool Granite. granite displays wide textural and lithological Magnetic data indicates that the body has a variation which is not mapped as separate more circular shape and is larger than shown units. It is a holocrystalline rock which ranges on the map. from fine- to coarse-grained. The main G220 Flowerdale Granodiorite minerals include alkali feldspar, plagioclase, quartz, muscovite, biotite, cordierite, This small, non-magnetic dumb-bell shaped tourmaline, and minor opaque minerals. pluton is aligned along the northwest trending GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 19

hinge of the major syncline which extends G279 Ingliston Granite through the Broadford township towards Flowerdale. It is a grey, fine-grained rock This small I-type intrusion lies 10 km southeast which contains biotite and muscovite, but is of Ballan where it intrudes Lower Ordovician highly weathered, and largely covered by sediments. It is partially covered by Permian alluvium from two creeks which cut across it. glacial deposits, Newer Volcanic lava flows and Williams (1964) noted at least two major quartz various fluvial sediments, making it difficult to porphyry dykes associated with the pluton. distinguish in the geophysical data. It is a non- magnetic, grey medium-grained granite which G221 Mount Disappointment Granodiorite contains biotite.

On the map this rock is shown to outcrop at G280 Mount Egerton Granite Mount Disappointment and adjacent to the Reedy Creek Anticline to the east. It is clear This roughly circular non-magnetic pluton has from the geophysical data that these are intruded Lower Ordovician sediments at separate plutons. The largest of these is an Millbrook. At the surface it is partially covered oval-shaped pluton at Mount Disappointment. by Newer Volcanic lava flows. It is an I-type, This is a non-magnetic, I-type granodiorite medium- to coarse-grained and partly which forms tor-covered hills surrounded by a porphyritic, biotite-bearing granite. prominent metamorphic aureole. Williams (1964) subdivided the pluton into two texturally G282 Barringo Granodiorite different rock phases; an inner medium- to coarse-grained granodiorite with abundant This pluton belongs to the Mount Macedon large perthitic phenocryst is surrounded by an Igneous Complex, where it has intruded and outer rim of medium-grained granodiorite. The metamorphosed younger extrusive igneous granodiorite consists of oligoclase, interstitial rocks. It is an I-type granodiorite which is quartz and biotite, and accessory zircon, mostly fine- to medium-grained, but may ilmenite and apatite. sometimes be porphyritic. It consists of 1-2 mm grains of zoned plagioclase, interstitial quartz The much smaller granite body to the east has and alkali feldspar, pale green and foxy red not been named or described. biotite, minor muscovite, and accessory apatite and zircon. G222 Glenvale Granodiorite Cobaw Batholith: G283, G284, G285 This tiny pluton forms a single outcrop in the alluvial valley of the Plenty River at Glenvale, This large batholith covers over 600 km2 only 3.5 km south of the Mount Disappointment between Carlsruhe and Pyalong. It intrudes Granodiorite, where it lies along the hinge of a and metamorphoses sediments of the north-south trending anticline. It was noted on Ordovician Castlemaine Supergroup, and cuts a map by Williams (1964), who indicated that it across the Cambrian sequence of the Heathcote contains a narrow porphyritic rim on its greenstone belt. Stewart (1966) identified four northern and eastern margins. The rock has main plutons in this batholith, but the smallest not been described in detail. of these, an elongate outcrop which extends from the northeastern margin of the batholith, G223 Black Range Granodiorite has since been included in the outer rim phase. The Cobaw Batholith incorporates the Pyalong, A small outcrop of granodiorite in the southeast Baynton, and Beauvallet plutons. These are all corner of the survey area is part of the much non-magnetic, but display varying radiometric more extensive Black Range Batholith which characteristics, which highlight the geochemical lies to the east where it forms part of the differences between the younger I-type rocks volcanic complex of the Archeron and Cerberon and the rock of the older S-type pluton. cauldrons. The batholith is composed of several unnamed plutons (McLaughlin, 1976; G283 Pyalong Granodiorite: surrounds the VandenBerg, 1977), only one of which is main body of the Cobaw Batholith as a narrow represented here. This is a non-magnetic S- rim. It represents an earlier pluton which has type granodiorite which forms a medium-sized been intruded by the smaller Baynton and body. It ranges from a quartz-biotite porphyry Beauvallet bodies. It is an S-type body which is to a coarse-grained biotite-bearing granodiorite. easily distinguished from the younger plutons by its radiometric signature. 20 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

G290 Harcourt Granodiorite This is a coarse-grained to porphyritic rock which differs from other plutons in this The Harcourt Batholith has been subdivided batholith as it contains biotite and muscovite, a into several plutons (Cherry & Wilkinson, small amount of cordierite, and accessory 1994), but the non-magnetic Harcourt zircon. Granodiorite is the only one of these to be exposed on the map, in northwestern G284 Baynton Granodiorite: forms the MELBOURNE. It intrudes and metamorphoses central portion of the Cobaw Batholith. This Ordovician sediments of the Castlemaine I-type rock has intruded the slightly larger Supergroup, and is an I-type, medium-grained Pyalong pluton, from which it is easily granodiorite which is occasionally porphyritic. distinguished by its red, potassium-rich It consists of orthoclase, andesine and/or radiometric signature. Its radiometric and labradorite, quartz and dark brown biotite, and magnetic characteristics are indistinguishable accessory zircon, ilmenite and sphene. from those of the Baynton Granodiorite. 2.4 Structure This medium-grained granodiorite contains plagioclase, alkali feldspar, quartz, abundant The structures across the map area may be biotite and hornblende, and accessory zircon. divided into three major structural domains, which reflect differences in structural style: G285 Beauvallet Granodiorite: forms a small pluton which intrudes both the central (G283) · Bendigo Zone: characterised by upright and outer rim phases (G284) at the southern chevron folded Ordovician rocks, margin of the Cobaw Batholith. This pluton has previously been referred to as the Cobaw · Melbourne Zone: dominated by simply folded Granodiorite, but this led to confusion, as the and faulted Silurian and Devonian rocks, Cobaw name also refers to the entire batholith. and VandenBerg (in prep.) described and named the pluton. It is an I-type granodiorite which is · Ballan Graben: characterised by major east- easily distinguished from the younger Pyalong west trending extensional faults. intrusion by its red, potassium-rich radiometric signature. Its radiometric and magnetic characteristics are indistinguishable from those Bendigo Zone of the Baynton Granodiorite. Most of the structures in the Bendigo Zone were This medium- to coarse-grained granodiorite formed during the Early Silurian Benambran consists of plagioclase, alkali feldspar, quartz, Deformation. This single but protracted event reddish-brown and greenish-brown biotite, and strongly folded and faulted the Castlemaine accessory hornblende. Supergroup but was followed by relative stability interrupted only by minor G287 Glenaroua Granite compressional events during the Middle Devonian Tabberabberan Deformation and This small non-magnetic pluton intrudes extensional tectonics associated with the Silurian sediments approximately 1.5 km east separation of Australia from Antarctica starting of the Cobaw Batholith. It is an S-type biotite- in the mid to late Mesozoic. bearing granite which contains accessory cordierite. The major deformation of the Castlemaine Supergroup was once regarded as a Tabberabberan event but the dating of granites (Richards & Singleton, 1981), and more recently the direct dating of metamorphic micas, has led to a better understanding of its timing. The deformation is now regarded as an early Silurian event (Willman, 1995; Gray et al., 1997).

Deformation of the Bendigo Zone developed in the thin-skinned style by detachment of the GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 21

Castlemaine Supergroup and a portion of the the Castlemaine and Bendigo goldfields has underlying Cambrian sequence from the lower shown a relationship between regional crust to form an allochthonous east-vergent fold structural style and the location of and thrust belt bounded to the east by the mineralisation (Willman, 1995; Willman & Heathcote Fault (Cox et al., 1991; Gray & Wilkinson, 1992). The evidence suggests that Willman, 1991a). In this way, the upper crust gold mineralisation is best developed in the was shortened by up to 65% over a horizontal hangingwalls of major faults, usually stepped fault some 15–17 km below the present back to the west a few kilometres. The location erosional surface (Gray, 1997). The listric of the Castlemaine, Maldon and Heathcote Heathcote Fault Zone represents the emergence goldfields follows this pattern whereas the of this major horizontal fault along the eastern Daylesford and Blackwood goldfields may be margin of the Bendigo Zone. The term listric anomalous although detailed structural describes the manner in which the fault flattens mapping has yet to be carried out in these from steeply west-dipping at the surface to areas. The theory is that third order horizontal at depth. The southern extension of mineralised west-dipping faults connect at the Heathcote Fault Zone is masked by Newer depth with the major listric faults thereby Volcanics and therefore the exact location of the tapping the flow of metamorphic fluids which eastern margin of the Bendigo Zone is were involved in the mineralising process. uncertain. The margin probably steps, or bends westwards from Monegeetta to link with the The Tabberabberan Deformation in the Bendigo Djerriwarrh Fault and from there may be Zone was only weakly expressed by the continuous with the Barrabool Hills greenstone development of conjugate cross faults, which occurrence. cut across earlier folds and mineralised structures, and possibly by the reactivation of Cambrian volcanics and sediments are inferred earlier faults. to underlie the Castlemaine Supergroup throughout most of the Bendigo Zone but are Melbourne Zone only exposed along major faults such as the Heathcote Fault Zone. Major second order The Silurian and Devonian sediments of the listric thrusts such as the Muckleford and Melbourne Zone were deformed during the Whitelaw faults are west of the Heathcote Fault east-west directed compression of the Middle Zone and no Cambrian rocks are exposed along Devonian Tabberabberan Deformation. At this these structures, instead, the oldest sections of time, westward movement of eastern Victoria the Castlemaine Supergroup occur in their occurred along the re-activated Governor Fault, hangingwalls. These faults separate older while eastward movement of the Bendigo Zone rocks in the highly strained hangingwalls from occurred along the re-activated Mount William much younger rocks in the footwalls to the east Fault. The sedimentary sequence between (Gray & Willman, 1991b). Deformation was these two major thrusts forms the Melbourne associated with lower greenschist facies Zone, and experienced substantial shortening, metamorphism which converted mudstone to accommodated by folding and faulting. slate. The grade of metamorphism is remarkably consistent throughout central The initial response to the regional, east-west Victoria showing only minor elevation near directed shortening of the entire sedimentary some major faults. East-west shortening sequence was the development of detachment produced very regular trains of closely spaced surfaces in weak layers of the succession. This north-south trending chevron folds associated is shown by the presence of a major thrust fault with strong cleavage development. Most major at the top of the Wilson Creek Shale (not shown and minor faults are west-dipping reflecting the on the map) which has truncated a significant sense of tectonic transport. portion of the stratigraphic succession. Regional scale north-south trending folds with Mineralisation developed throughout the wavelengths of several tens of kilometres deformation within structures generated by fold developed. Detachment surfaces ramped up and fault growth but reached a peak late in the through the folding sediments, and breached later stage. Gold-quartz mineralisation occurs the regional anticlines as emergent thrusts as narrow vein style deposits hosted by the with dip-slip displacements. These include the deformed Castlemaine Supergroup. At the Moormbool Fault, but are often not mapped mine scale, mineralisation is controlled by regionally due to poor exposure. To the north bedding, folds and faults and is associated with in HEATHCOTE and NAGAMBIE these faults weak wall rock alteration. Detailed mapping in 22 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

often correspond to areas of known gold on the downfaulted sides. The VIMP mineralisation. aeromagnetic data indicates that several unmapped faults occur north of the Ballan Transpressional shortening between the Graben and are aligned with outliers of Melbourne Zone and the eastern Victorian block Permian sediments. The faults may be early along the Governor Fault along the Cretaceous given their similar orientation to northwestern margin of the Melbourne Zone faults in southwestern Victoria although there (R.A. Cayley pers. comm.) gave rise to east-west are no known Cretaceous sediments in the trending folds to the north, and warped the Bacchus Marsh area (C. Lavin, pers comm. earlier-formed north-south trending folds in the 1997). Singleton (1973) suggested that western part of the Melbourne Zone to give subsidence occurred in the Ballan Graben them doubly plunging, curvilinear axial traces. intermittently from the Permian resulting in The regional effect of this is a structural deposition of the thick fluvioglacial sequence. interference pattern of basins and domes. The WNW trending faults became inactive prior to the main movement along the set of north The Silurian and Devonian rocks of the western trending faults such as the Rowsley and Melbourne Zone in the map area therefore form Djarriwarrh faults. These faults may be a series of simply folded and faulted anticlines reactivated Palaeozoic structures. The Rowsley and synclines. These doubly plunging, north- Fault is marked by a scarp produced mainly by south trending folds have curvilinear axial Pleistocene movement associated with the Port traces which can often be traced for several tens Phillip sunkland. of kilometres. Smaller parasitic folds are generally less continuous, but have not been mapped in detail. There are few major faults mapped in this region, although it is assumed that faults occur in the hinges of most of the major folds.

Cleavage is rarely seen, and was either not well developed, or is poorly preserved. Work in the Kilmore district by VandenBerg (1992) shows the presence of a poorly preserved but widespread cleavage which is unrelated to the Tabberabberan folds on the map. It may be the result of sinistral strike movement on the Mount William Fault, or it may be a Carboniferous feature, developed during the Kanimblan Deformation in which the Upper Devonian rocks of Gippsland were folded (VandenBerg, 1992).

Ballan Graben

In the Late Jurassic Victoria was subject to extensional tectonics as rifting was initiated between Australia and Antarctica. Break-up occurred either in the mid-Cretaceous (Cande & Mutter, 1982) or Late Cretaceous (Lavin, 1997) and sea floor spreading after the break-up continued to affect MELBOURNE from the early Tertiary. The WNW trending normal faults of the Ballan Graben in the Bacchus Marsh area are probably related to this continuous extension. The main bounding faults are the Greendale–Coimadai faults to the north and the Spring Creek Fault to the south. These major faults are part of a parallel set along which Permian sediments are preserved GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 23

3 Economic geology Production from the various goldfields is presented in Table 2 and Figures 5 and 6. The data for Figures 5 and 6 is derived from the Mines in MELBOURNE have produced in Quarterly Reports of the Mining Surveyors and excess of 300 t of gold, 400 t of antimony as well Registrars and the Mines Department Annual as diatomite, iron ore and magnesite, and Reports 1864-1996. currently produce substantial quantities of kaolin, brown coal and dimension stone. Maldon & Muckleford Goldfields Extractive industries produce sand, clay and gravel valued at about $100 million annually, The Maldon goldfield ranks as the fourth mostly for the Melbourne market. The location largest reef field in Victoria. Alluvial gold of the goldfields and mineral resources within attracted the initial rushes in 1853, but the MELBOURNE are shown in Figures 2 and 4. diggings were not particularly rich or extensive, and by 1857 quartz reef mining predominated. The following styles of mineralisation are Total alluvial gold production is estimated at recognised within MELBOURNE: about 9 t, and reef gold production was about 54 t for the period to 1926 when large scale · gold-bearing quartz vein deposits; underground mining ceased (Morgan, 1988). · alluvial gold deposits; More than 30 reefs were mined at Maldon, but · antimony vein deposits; most production came from high grade · granite-hosted quartz vein gold deposits; oreshoots on the Nuggety, Eaglehawk, · residual haematite; Linscotts/Union (all in BENDIGO), Beehive- and various non-metallics, including: German, and the North British or Parkins lines of reef. The deepest workings, to about 670 m, · brown coal deposits; were in the South German mine. Unlike the · residual and transported kaolin; Bendigo reefs, those at Maldon were not · dimension stone; particularly rich below about 75 m (Bannear, · diatomite 1993). Other characteristics of the field were the very hard ground at depth and the Gold deposits occur in two major provinces refractory nature of the ores, due to the which coincide largely with the Bendigo and presence of sulphides of iron and bismuth. Melbourne structural zones (Fig. 1). The former Roasting of the ores, either before or after is host to the major gold deposits and is crushing, was therefore commonly used to deal characterised by a more intense regional with such ores. A revival of mining at Union metamorphic regime, with most mineralisation Hill just north east of Maldon commenced in taking place somewhat earlier than in the the mid 1970s with limited open cutting by Melbourne Zone to the east. The Melbourne Lone Star Exploration. Its lease was taken over Zone is characterised by more open folding, in 1985 by Triad Minerals who developed the relatively modest gold mineralisation, and a open cut with considerable success for several strong association between gold and stibnite. years (Morgan & Woodland, 1990). Alliance Gold Mines N.L. acquired the operation in 1994 3.1 History of mining and has developed commercial scale underground workings at Union Hill Gold (Eaglehawk and Linscotts Reefs), as well as investigating several other prospects on the The most productive goldfields in Maldon field. Total production from the Union MELBOURNE lie in the western third of the Hill area by Triad/Alliance from 1987/88 to sheet area, within the Bendigo Zone, and 1995/96 was about 1,950 kg of gold. include the famous Castlemaine, Daylesford, Egerton-Gordon, Blackwood-Trentham, Historically, underground mining at Maldon Lauriston-Taradale fields, and the southern reached a depth of over 600 m in the South part of the Maldon field. In contrast, German mine, and altogether 15 shafts production from goldfields within the exceeded 300 m in depth. Mines with Melbourne Zone in the eastern two thirds of production greater than 1,000 kg are listed in MELBOURNE has been relatively minor. The Table 3. history and geology of these lesser goldfields are presented together in Section 3.2. 24 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Figure 4 Mineral resources within MELBOURNE. Table 2 Gold production from goldfields within MELBOURNE

Primary gold Deep lead Shallow alluvial Total gold Goldfield production average gold production gold production production Comments Reference (kg) grade (g/t) (kg) (kg) (kg)

BENDIGO ZONE

Castlemaine-Chewton, 29 800 10.5 n/a 143 300 173 100 Alluvial production very approx. Willman (1995) Fryers Creek Maldon 56 400 28.0 9 300 65 700 Reef gold production to 1995/96 Whiting & Bowen (1976) & Cherry & Wilkinson (1994) Daylesford 18 500 13.8 +2 500 n/a + 21 000 Shallow & deep lead alluvial workings Ramsay & Willman (1988) significant in this area, but few & (Canavan, 1988) production records. Royal Oak mine alone produced 2,500 kg Mount Egerton-Gordon 15 550 12.0 11 500 27 000 Roberts (1984) Taradale-Malmsbury, +7 496 21.0 +134 n/a +7 630 Shallow & deep lead alluvial workings John Taylor & Sons (1967) Drummond-Lauriston significant in this area, but few production records. Standard Lead produced 134 kg (Canavan, 1988) Newstead, Guildford, n/a n/a 7 618 7 618 Production from major dredging and Canavan (1988) Strangways sluicing operations on Castlemaine shallow lead Blackwood-Trentham +5 276 25.0 n/a n/a +5 276 Deep lead production probably minor John Taylor & Sons (1967

MELBOURNE ZONE

Primary gold Alluvial gold Total gold Goldfield production average production production Reference (kg) grade (g/t) (kg) (kg)

Reedy Creek 886.3 30.1 10.6 892.5 Quarterly Reports of the Sunday Creek 610.7 16.9 3.8 614.5 Mining Surveyors and Yea 189.8 63.0 10.2 200.1 Registrars Donnybrook 47.3 156.0 n/a 47.3 and Tea-Tree Creek 40.8 44.2 0.5 41.3 Mines Department Annual Kilmore 12.5 2.7 22.8 35.3 Reports, 1864-1996 Strath Creek 30.0 55.0 .3 30.3 and King Parrot 2.1 15.6 n/a 2.1 Kenny, 1937a & 1937b 26 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Figure 5 Primary and total gold production for MELBOURNE by Historic Mining Division. For locations of the divisions, refer to Figure 4.

Table 3 Mines with production greater than 1,000 kg, Maldon Goldfield (after Bowen, 1974)

Reef line Mine Gold production (kg)

Nuggety 9,360 Eaglehawk or Union Eaglehawk Consol. 9,753 Union 5,532 Beehive and German Beehive 4,105 Great Western Cymru 1,960 South German Co. 5,387 Old South German. 1,420 Parkins North British (Oswalds) 7,540 Victoria Victoria Co. 3,100 Derby United 1,844 Nelson South German Extended 1,688 Lyle-Exhibition 1,820 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 27

Figure 6 Total gold production for MELBOURNE by Historic Mining Division and year. For locations of the divisions, refer to Figure 4. Note that parts of some divisions fall outside MELBOURNE and therefore some of the production shown, relates to areas lying adjacent to MELBOURNE. This is significant in the case of Tarrengower. Production for the divisions in the upper graph are for the period 1864 to 1996. Production for divisions in the lower graph are for the period 1850 to 1996. 28 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Table 4 Muckleford Goldfield production (after Willman, 1986)

Reef line Period Ore Gold Grade treated (t) production (kg) (g/t)

Fentemans up to 1897 1282 26.8 20.9 1897-1903 3519 44.2 12.6 Smiths 1860-1867 544 7.4 13.6 1884-1885 498 1.2 2.4 Dunns 1889 22.4 0.2 8.9 Red, White & Blue 1874 2883 21.6 7.5 1909-1915 4523 73.7 16.3 Blow 1899-1900 562 16.3 29.0 Nuggety 1899-1910 8469 115.9 13.7 Thornhill 1860-1887 10826 155.4 14.4

The Muckleford Goldfield lies about 8 km washdirt where their European counterparts southeast of the Maldon field, between it and left off. the Muckleford Fault. The workings on the Muckleford field rarely exceeded 80 m in depth. Lack of water was a major hindrance to mining Much of the early production from the field has in the drier months, until the advent of water not been recorded, but some of the major yields channels from the Loddon River in the early are given in Table 4. 1870s (Bannear, 1993). The improved water supply facilitated the processing of vast Castlemaine, Chewton-Fryerstown Goldfields reserves of low grade material by means of ground sluicing. A major boost to alluvial gold The first official record of gold discovery in this production occurred in the late 1800s, with the region is that of Christopher Peters who found introduction of high pressure hydraulic sluicing a gold bearing quartz vein at Specimen Gully and dredging. The major alluvial tracts were north of Castlemaine, in July 1851. In worked repetitively to obtain increasingly fine November 1851, diggers were rushing to gold, and although dredging activity peaked at Golden Point on Forest Creek, where shallow around 1910, it continued until 1943. alluvial gold was readily found. Gold escort returns for the early years of mining in the The development of quartz reef mining was Castlemaine and Fryers Creek Mining impeded in the early 1850s by the lack of Divisions testify to the huge yields from efficient, mechanised equipment to liberate the alluvium of both Quaternary and Tertiary age. gold from quartz. Steam driven crushing From late 1851 until late 1863 about 131,165 kg machines were first introduced in 1855 and of escorted gold, mainly of alluvial origin, is their use became widespread as companies estimated to have come from these Divisions. were formed to provide the necessary capital for This represents about 75% of the total, officially reef mining on large leases. Many companies recorded production of about 173,091 kg from collapsed in the early 1860s due to over these Divisions from 1851 to 1993. A complete capitalisation and poor ore reserves, with a listing of mine by mine production is given by consequent return to small scale mining. Willman (1995). The near-surface alluvium Company activity and reef mining were was easily treated by the miners, operating revitalised briefly in the early 1870s with the individually or in small parties, and using expectation of high yields from deep mining, simple equipment such as gold pans, puddling similar to those at Bendigo. However tubs, cradles and sluice boxes. Puddling investment capital was often depleted before machines were introduced in about mid 1854 as the operators gained a proper understanding of a popular means of washing fines from clay-rich the structural controls on mineralisation at gravels. A notable feature of the alluvial fields Castlemaine, which did not follow the Bendigo was the presence of the Chinese miners who pattern. Quartz mining continued through the commonly persevered with mining of low grade late 1800s and early 1900s with varying fortunes, but was adversely affected during GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 29

periods of recession and war. Most reef gold a series of rich finds. Interestingly, most production came from a long narrow belt of successful mining was being conducted on country extending for more than 9 km from the private land, but only after careful negotiation northern end of the Chewton field south to with landowners. Both types of mining Fryerstown (Whiting & Bowen, 1976). This belt remained reasonably buoyant until the late contains several mines which produced more 1880s however they were not without lean than 500 kg of gold each, including the Francis periods and were partly characterised by non- Ormond, Rowe Brothers, New Era, Spring genuine speculative ventures. The Lauriston Gully Co. and Wattle Gully Gold Mine. Gold field had collapsed by the mid 1870s leaving the mining ceased at Fryerstown before 1890. The Taradale field as the only major centre of Wattle Gully Mine at Chewton has been activity in the Division. Since 1888, mining has outstanding in terms of its productive life, total only been conducted on a small scale. The last gold yield and history of modern exploration serious mining took place at the Phoenix mine with over 10,400 kg of gold produced from 1935 on the northern end of the Old Hughes line of to 1993. There has been little reef gold reef at Taradale, and closed down in 1957. production from the Castlemaine goldfield in Production from major reef mines is shown in recent years, despite a series of exploration Table 5. programs since 1965. Most of the recent programs have focussed either on the main Daylesford Goldfield Chewton-Fryerstown mineralised zone, including the Wattle Gully mine, or the Eureka- This field, originally known as the Jim Crow Spring Gully zone to the west (Willman, 1995). diggings, was discovered in 1852, and proved to be exceptionally rich in alluvial gold (Whitelaw Taradale - Malmsbury, Drummond North, & Baragwanath, 1923). Gold was found in high Lauriston Goldfields level alluvium on ridge crests and spurs; in deep leads beneath basalts; and in present day Alluvial gold was discovered along the Coliban stream alluvium. By the mid 1850s gold River near Lauriston in 1851, closely followed mining was well established at Daylesford and by discoveries along Back Creek at Taradale several outlying fields were also being (Bannear, 1993). Compared to the prospected, including Yandoit and Coomoora exceptionally rich shallow alluvial ground (Bannear, 1996). Most of the mining population worked in the neighbouring Castlemaine field was engaged in shallow alluvial mining from during the 1850s, that of the Taradale Mining the late 1850s to mid 1860s. Following Division proved to be very poor. In 1856 some exploitation of the near-surface alluvium by shallow alluvials along Back Creek were shafts and drives, races were constructed for followed to the east and into deep leads beneath widespread puddling and sluicing operations. a basalt cover. These deep leads, which were Near Daylesford, the deep leads lie above creek not highly productive, include the Belltopper - level and were accessed by tunnels. Many Ironstone, Scorpion, Cambrian and Talbot kilometres of lead were worked by driving and leads. Auriferous quartz reefs were discovered shaft sinking, particularly to the north-east, and worked along with alluvial deposits during with gold grade decreasing away from the the mid to late 1850s. By 1855 several claims auriferous belt. Shaft sinking through basalt on Hughes or Achilles Reef at Taradale were commenced in the early 1860s, and the most producing high returns. Most of the major reef successful deep lead mining commenced on the lines in the Division had been discovered by the Township Lead at the Italian Hill workings, end of the 1850s. Gold grades were found to be following to the north east towards Coomoora. rich near surface but declined markedly with By 1864 deep lead mining was buoyant, having depth towards the water table at around 30 m. been supported by large company capital which financed equipment such as drills and steam Reef mining in the 1860s failed to attract engines. Activity declined after 1865, with sufficient company investment to allow major minor revivals including those at Mount development below water level, and so alluvial Franklin (late 1870s), Rocky Lead near mining, partly by the Chinese, continued to Smeaton (early 1880s), and Yandoit (1930s, dominate during this period. Sluicing was the 1964-69). favoured method for working the poor alluvial flats. Deep lead and quartz mining only gathered momentum after the mid 1860s, with 30 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Table 5 Production from major reef mines, Taradale - Malmsbury, Drummond North, Lauriston Goldfields (after John Taylor & Sons, 1967)

Region Mine Ore Gold Grade Sulphide minerals treated (t) production (kg) (g/t)

Taradale Fenton 35 000 560 16 United Kingdom 50 675 653 13 Nelson 28 000 218 8 Adventure 4 000 93 23 pyrite Plutus 20 000 498 25 pyrite North Phoenix 1 800 56 31 Drummond North Queens Birthday 40 000 1209 30 stibnite, pyrite O'Connors Freehold 43 322 1207 28 stibnite, pyrite, sphalerite Egyptian 15 000 280 19 Lauriston Glengonner 15 000 187 12 Central Energetic 16 000 253 16 Energetic 251 North Star 10 000 161 16 North Energetic 2 000 31 16 pyrite Russells Reef 75 000 1432 19 stibnite, pyrite Amalgamated No.1 South Russells 15 000 236 16 pyrite, galena South Russells 171 stibnite, galena, pyrite

Reef mining commenced early in 1854 on the Blackwood - Trentham Goldfield Mauritius line and shortly after on the Cornish reef. By 1856, a belt of auriferous reefs A rush to the alluvial riches of the Lerderderg between Daylesford and Yandoit had been River and its tributaries began in mid 1855. prospected, but the most successful early mines One of the mining villages, at Golden Point, were those at Wombat Hill (now Cornish or was later to become the township of Blackwood. Argus Hill) overlooking Daylesford. The rich The easily won gold was soon depleted, and Specimen Hill, Ajax and Nuggety reefs were miners struggled to make a profit after 1856. opened in about 1857. The Specimen Hill Q. M. The river bed was worked repeatedly, using Co. mined profitably between 1862 and 1877, sluice boxes, pumps and water wheels, but and the reorganised Cornish Co. dominated reef puddling was a rare practice, (Bannear, 1996). mining in the 1870s and 1880s. Both By the 1870s sluicing was mainly performed by companies employed massive mining and the Chinese, whose persistence enabled many processing equipment, the former operating 17 to return to their homeland with considerable heads of stampers, Hungarian and Chilean wealth. In the early 1870s, two companies also mills and a roasting furnace. During the 1870s crushed cemented gravels at Golden Point, to companies also commenced using the release the contained gold. chlorination process to treat sulphide ores. Little profitable mining took place in the 1890s. At the end of the alluvial rush, miners A revival occurred in the early 1900s, commenced reef mining on two lines, Barrys particularly on the Ajax line, but was halted by and Yankee, and later on Simmons and World War 1. Subsequent bursts of activity in Johnstons. Initially, small parties worked the the mid 1930s and 1947 produced only minor reefs from adits driven into the hillsides, with returns. Production from the major reef mines internal shafts which rarely extended far below is shown in Table 6. water level. Steam and water power were both used for crushing. Major company investment GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 31

Table 6 Production from major reef mines, Daylesford Goldfield (after Baragwanath, 1953)

Mine Period Ore treated Gold Grade (t) production (g/t) (kg)

Cornish Co. 1856-1889 178 825 1 606 9 North Cornish 1886-1891 139 722 1 708 12 New Cornish 1903-1911 53 322 861 16 Rising Star 1877-1890 233 692 2 386 10 Ajax North 1910-1926 126 702 1 456 11 Ajax 1905-1928 178 648 3 835 21 Ajax Central 1910-1918 89 797 1 638 18 North Nuggety Ajax 1910-1919 77 195 1 537 20 Nuggety Ajax 1905-1919 62 019 894 14 Frenchmans Reef 1906-1916 31 343 329 10 began in 1868 with mixed fortunes and it was from which about 800 t of concentrate and hand the small cooperatives who maintained the picked ore averaging about 50% antimony were industry. However the Sultan Company mined obtained (Bowen, 1970). Gold was also successfully on Barrys Reef for ten years and obtained from the concentrates. The mine is produced over 2,000 kg of gold. In the early the third largest producer of antimony in the 1870s, several new reefs were discovered, State, after Costerfield and Ringwood. Small including Browns, about 13 km southwest of mine workings have been developed on stibnite Blackwood, where the town of Blakeville was deposits near Blackwood and Malmsbury, but established. By the late 1870s, production in with no recorded production. the district was in decline with several companies, including the Sultan, closing down Iron ore was mined in the 1870s from a and selling off machinery. A few new ferruginised Tertiary sediment at Lal Lal, with companies purchased plant and attempted to ore grading up to 49% iron. The ore was revive mining in the 1880s but only the New smelted on site in a blast furnace, the remains North Britain Company achieved real success. of which are still standing. Large scale reef mining in the district ceased with the closure of its mine in 1889. During the Industrial minerals 1880s attempts were made at deep lead mining beneath basalt in the Trentham area, but Kaolin deposits of various types occur in apparently with little success. Production from MELBOURNE and have a long history of major reef mines is shown in Table 7. development. Some of the oldest workings are the underground mines developed in very pure Other metals kaolin derived from dyke rocks. They include the Egerton mines which date back to the last Antimony was one of the first base metals to be century and the Lal Lal mine which was first discovered in Victoria, perhaps due to the worked in 1936 and which is active at present. proximity of several deposits to Melbourne. Weathered granite on the margin of the Lal Lal The Coimadai antimony deposits, located about swamp has been mined from open pits for 15 km north northeast of Bacchus Marsh, were kaolin intermittently since late last century for discovered in 1887 and were worked use in manufacture of paper and ceramic intermittently until 1915 (Fisher, 1953). From products. Sedimentary kaolinitic clays of the 1942 to 1944 the mine was operated by the Parwan Valley, in particular the Darley and Lal Commonwealth Government to help meet the Lal areas also have a long history of use in wartime demand for antimony. Total mine manufacture of refractory bricks and ceramic production is probably around 6,000 t of ore products. The Darley Fire-brick Co. Pty Ltd, 32 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Table 7 Production from major reef mines, Blackwood - Trentham Goldfield (after John Taylor & Sons, 1967).

Region Mine Ore Gold Grade treated (t) production (kg) (g/t)

Sultan Group Sultan 82 000 2 051 25 Mounters 308 Amelia 5 070 158 31 Sultana 48 Golden Hope 2 925 43 15 North Sultan 31 Other mines 93 Simmons Reef Group Cornish 120 Big Hill 99 Crown 3 340 80 24 Imperial 64 Other mines 4 500 87 19 Briton Group Red, White & Blue 333 New (North) Briton 22 800 155 7 Old (North) Briton 47 Easter Monday Group Easter Monday 6 921 222 32 True Blue 97 Grace Egerton 10 000 80 8 Yankee Group Morning Star 16 000 498 31 Yankee 7 860 135 17 Victoria 154 Miscellaneous New Sultan 6 166 134 22 Rip van Winkle 21 000 240 11

established in 1902, extracted clay initially from a large pit in the hillside adjacent to its Diatomite deposits lying beneath basalt at plant. Excessive overburden thickness forced Redesdale, Newham and Moranding have been the company to develop the clay seams from mined mainly during the 1940s by means of underground. Mining operations here ceased adits, for use in insulation, and as a filler in many years ago, but open cuts still remain paint and rubber. active in the Parwan Valley. The area has a long extractive industry history, Granite has been quarried for dimension stone with approximately 7.5 million tonnes per year continuously in the Harcourt / Mount of construction materials including hard rock Alexander area since 1859. It was used widely (mostly basalt), clay, sand and gravel worth for structural and decorative purposes in about $100 million quarried from Melbourne buildings from the 1880s onwards, MELBOURNE. and has maintained a strong presence in monumental stonework for much of this century. Current production is of the order of 5,000 tonnes per year (King & Weston, 1997). Other traditional sources of building and paving stone are basalts at Malmsbury, sandstone at Bald Hill near Bacchus Marsh, and slates near Castlemaine. GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 33

3.2 Gold occurred during or immediately following major periods of compressional deformation, including The history of alluvial and primary gold mining the Late Ordovician - Early Silurian in Victoria has demonstrated a strong (Benambran) and Middle Devonian spatial/genetic association between these two (Tabberrabberan) Deformations. In central main types of occurrence. Areas of high yield Victoria, marked changes in mineralisation for alluvial gold lie in close proximity to those styles are observed in passing from early- for primary gold. In the goldfields of formed deposits in the west to later ones in the MELBOURNE, as for other fields, alluvial gold east. Most primary deposits in the Stawell and discoveries and early workings preceded and Bendigo zones formed during regional led to primary gold discoveries. For most fields, metamorphism and thrusting, between 450 and gold production records for the early years of 420 Ma (Foster et al., 1996). In both the mining, and particularly for alluvial gold, are Melbourne and Bendigo zones, gold very poor. However it is clear that the relative mineralisation of lesser intensity occurred contributions of shallow alluvial, deep lead around 380 and 370 Ma, during or following alluvial and reef mining to total historical intrusion of felsic plutons and dykes (Arne et production, varies considerably between al., 1996). goldfields, partly a reflection of the quite variable pattern of Cainozoic erosion/deposition On a regional scale, auriferous quartz veins across the area. For example Maldon was tend to be clustered within belts or “fields” essentially a reef field, while shallow alluvial which are typically a few kilometres wide, may workings produced the greatest yields in the be several kilometres long, and which are neighbouring Castlemaine field (Table 2). elongated parallel to the regional fold and fault Significant alluvial mining, which extended into trend. The reasons for this clustering are not high level and deep lead gravels, occurred at clear. Cox et al., (1991) have suggested that the Daylesford and Taradale - Malmsbury, in morphology of the fields, together with the fault addition to the reef mining. Most of the other controls on individual deposits and groups of fields are characterised by reef and subordinate deposits, point to a relationship with major nearby shallow alluvial workings. fault zones that have tapped auriferous fluids from deeper crustal levels. The development of The general characteristics of primary and hydraulic fracture vein arrays that host alluvial gold occurrences are discussed below, mineralisation indicate that the enclosing rocks followed by more detailed descriptions of were subject to anomalously high fluid pressure goldfields. The latter descriptions relate mainly and high fluid flux during mineralisation and to primary gold, for which the future fault movement. A clear spatial relationship exploration potential is perhaps greatest. between mineralised zones and major faults has not been established, although in the Bendigo Primary gold - general occurrence Zone, goldfields tend to occur at or near the hanging wall of major faults. Refolding or interference folding may also have produced All significant primary gold occurrences in favourable sites for gold deposition. Victoria appear to be structurally controlled. Most deposits worked to date have been fissure The major high angle, west dipping reverse fillings of auriferous quartz, emplaced within faults presently exposed at surface are thought faults, tension gashes and fold hinges. Within to level out and splay from subhorizontal MELBOURNE they are hosted in the turbiditic detachments at shallow crustal levels (Fig. 7). sandstone and shale sequences or If such faults formed channelways for metasediments of the Lachlan Fold Belt. mineralising solutions, the deep sources for the Several of the goldfields in the west, hosted in gold are likely to have been removed laterally to Lower Ordovician rocks (Castlemaine the west of the final depositional sites. The Supergroup) of the Bendigo Zone, rank amongst primary source of gold and associated the highest producers in the State. The major mineralisation is highly conjectural. Some of host rock lithologies are sandstone, mudstone the more recent theories suggest that gold may (now slate), and black shale. To the east, gold have been scavenged from an extensive sheet of mineralisation of much lesser intensity, occurs mafic volcanics underlying the sediments, or within Siluro-Devonian rocks, primarily alternatively from deeper crustal material. siltstones, of the Melbourne Zone. Gold- Granitic magma has also been suggested as a sulphide mineralisation appears to have 34 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 35

possible source for gold and various other faults may host “neck” reefs lying above the metals which may have been concentrated in, saddles, with associated extension vein arrays and transported by hydrothermal fluids evolved or “spurs”. “Leg” reefs are the bedded from the granitic melt. There is little evidence extensions of the saddle reefs, down the limbs for a direct, genetic association between gold of the folds. “Trough” reefs are inverted saddles deposition and granite emplacement. However occurring in synclinal hinges, and are less some granite intrusions may have acted as heat common than anticlinal saddles. Vein sources which mobilised mineralising fluids and microstructures, particularly crack-seal directed them into favourable depositional sites. features, provide evidence that the quartz in Alternatively, mineralisation and magmatism some of the major laminated fault-fill lodes and may have an indirect link through a major extension veins was introduced incrementally, thermal event which influenced each activity with numerous accretion events. Furthermore, independently. Some of the stibnite-gold relationships between minerals in such veins occurrences of the Melbourne Zone appear to show that gold has been introduced throughout have at least a temporal association with Late most of the vein growth history. Individual Devonian felsic magmatism. A few of them, deposits may have their own characteristic including the Clonbinane deposits, have been combinations of structural settings, and few emplaced within fractures in diorite and deposits display only one style. porphyry dykes. Alteration around veins is widespread but It has been suggested (Cox et al., 1991, Cayley subtle, common phases being white micas, & McDonald, 1995) that for the west-central carbonates and sulphides (Phillips and Hughes, goldfields of Victoria, gold and associated base 1996). Muscovite, ankerite, pyrite, metals may have been transported by silica- arsenopyrite, chlorite and albite are common, rich, low salinity metamorphic fluids in a and calcite, siderite, magnesite, pyrrhotite, mesothermal environment. Precipitation of the galena, sphalerite and chalcopyrite occur at metals and silica may have been caused by some localities. Vein minerals are dominated small changes in fluid chemistry, resulting from by quartz which usually constitutes over 95% of a drop in pressure, temperature, or most veins. Carbonates such as ankerite, fluid/wallrock interactions. The latter may calcite and dolomite are common in veins, with account for the close association in some micas, including chlorite, as accessories. The goldfields, between high gold concentrations major sulphide phases are pyrite and and the presence of black graphitic and pyritic arsenopyrite. Gold in quartz is commonly slates, or “indicator” type slates. In this type of coarse, occurring in scattered, isolated grains or occurrence, gold may occur without any obvious filaments, and it also occurs as inclusions in sign of introduced quartz mineralisation. sulphides. Coarse, free gold is commonly found in veins near their intersection with pyritic- The most important structural sites for carbonaceous slates. Silver is a minor auriferous quartz veins appear to be dilatant component of most gold deposits, and bismuth jogs on reverse faults, extension fracture arrays and tungsten minerals are restricted to deposits near faults, and structures near fold hinges, within the contact aureoles of granite plutons, including saddle reefs. Quartz reefs within e.g. Maldon. Significant antimony bedding concordant, high angle reverse faults concentrations are restricted to ores containing rarely have major extension vein arrays or stibnite which mainly occur in the Melbourne “spurs” in the hangingwall or footwall (Cox et Zone (Hughes et al., 1997), and which are not al., 1991). Bedding discordant fault segments present in the major gold producing areas. are normally accompanied by vein arrays in Arsenopyrite is commonly associated with both walls, and faults with major reverse auriferous quartz at Bendigo, Maldon and displacements host some of the largest gold many other goldfields; and primary arsenic deposits in the Bendigo Zone. Simple saddle anomalies may extend up to 100 m around structures form when flexural slip along mineralisation. bedding planes during fold tightening produces dilation at the hinge zones, and therefore depositional sites for quartz. Saddle structures are usually more complex than this, and commonly, with the progression of folding, bedding plane slips have fractured across the fold hinges to form discordant faults. Such 36 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Secondary (alluvial) gold deposits - 2. Shallow to deep lead deposits formed during general occurrence the Cainozoic in ancient drainage systems, and later buried by basalt and/or alluvium. Prolonged erosion during the Upper Palaeozoic and Mesozoic times had exposed vast areas of The deep lead deposits have conventionally auriferous bedrock by the Tertiary period. been assigned to the Calivil Formation of Continued erosion, and concentration by fluvial Late Miocene to Early Pliocene age. This processes up to the present day, have acted to formation outcrops over large areas near produce the alluvial gold deposits, generally in Castlemaine (Willman, 1995), Campbells close proximity to the primary sources. The Creek, Guildford and Newstead. In these Cainozoic stratigraphy of auriferous sediments areas the highest gold grades were has not been clearly elucidated, due to a lack of encountered in the coarse gravels at the base age fixing data and difficulty in correlation of the deposits. The gravels were mined between discontinuous patches of sediments. initially by means of shallow shafts and Primary gold sources which remain exposed for tunnels, and later by large scale sluicing and a considerable time can produce secondary dredging. Valley-fill deposits extend for concentrations of gold in diachronous units, many kilometres beneath basalt in the given favourable erosional/depositional north-western part of MELBOURNE. They conditions. Thus in the Loddon Lead System represent tributaries within both the Loddon for example, the headwaters may contain gold and Campaspe lead systems. Bedrock bearing alluvium at shallow depth in youthful hosted gold from both the Castlemaine and gullies, which passes downstream into older Daylesford goldfields was shed into alluvium beneath an ever-increasing thickness tributaries of the Loddon System, and of sediment cover (Canavan, 1988). Further similarly gold from the Taradale, Lauriston down the lead may pass beneath a cover of Plio- and northern part of the Trentham fields Pleistocene basalt and remain auriferous until was shed into the Coliban - Campaspe Lead. eventually it widens and gold grades diminish, Although the deep leads extend well but its course may still be traced further, downstream from these goldfields, no beneath Miocene marine sediments. Despite significant underground mines were the continuity of some lead systems through developed in the leads, beyond the time, gold bearing alluvial deposits are immediate vicinity of the primary sources. commonly placed in categories as follows, for The last underground deep lead mine in ease of description: Victoria was the Lady Jennifer near Yandoit. 1. High-level gravel deposits formed in early Cainozoic drainage systems, but later 3. Shallow alluvial and eluvial deposits uplifted and eroded, leaving them as isolated relating to modern drainage systems. remnants above present stream levels. The present drainage system was Deposits of “high-level” alluvial gravel and established in the Plio-Pleistocene period. sand with occasional kaolinitic clay lenses Mining of reef gold in almost all goldfields are found scattered across the highlands in was preceded by the discovery and mining of north-central Victoria and extend subsurface shallow alluvial gold. Eluvial deposits at the into deep lead systems. They belong to the base of outcropping reefs commonly carried White Hills Gravel of possible Palaeocene rich gold, and merged with auriferous age (Cherry & Wilkinson, 1994), and are colluvium, which in turn merged with the commonly auriferous. The type locality is at alluvium. In some areas, notably White Hills north of Bendigo, where cross Castlemaine, the Quaternary gravels have bedded quartz conglomerate up to 20 m been at least partly sourced from nearby thick occurs as a valley fill deposit Tertiary (Calivil Formation) gravels, with (Wilkinson, 1988). They are very restricted the contained gold having the same source. in MELBOURNE but notable occurrences In major valleys the thickness of Quaternary are the Belltopper Lead in the Malmsbury alluvium in Shepparton Formation Goldfield and hill crest alluvium at equivalents reaches up to 15 m. Some of the Daylesford. larger streams carried gold well downstream from the sources. Within the Castlemaine - Chewton and Fryers Creek fields, virtually the whole area of the late Cainozoic alluvial GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 37

deposits was mined for gold. The auriferous important part of the ore mined by Triad gravels of Forest Creek were present in two Minerals N.L. from the Union Hill open cut layers; an upper one consisting of hard mine between 1988 and 1992. According to conglomerate or "cement" with slate, Phillips and Hughes (1996), most ore shoots sandstone and quartz pebbles, and a lower occur in relatively thick bodies of quartz within quartz gravel in contact with weathered dilatant jogs. Mining widths were typically bedrock or "pipeclay" (Willman, 1995). The between 1 and 3 m. Maldon was noted for its lower zone was commonly very rich at its exceptional gold grades (averaging 28 g/t base, and the gold penetrated up to 60 cm between the 1860s and 1926), and repetition of into bedrock crevices. vein structures. The Muckleford reefs lie mainly about 2 km west of the Muckleford Bendigo Zone Fault which is apparently unmineralised. They are generally controlled by steeply west dipping Only the major goldfields with relatively high faults (Willman, 1986) and consist of both historical production are described here. More laminated and massive quartz. detailed site by site data for the other goldfields is presented in the database that accompanies Alteration surrounding the veins appears as a this report. narrow selvage rich in biotite and/or muscovite, and as extensive carbonate and pyrite spotting. Maldon and Muckleford Goldfields Biotite selvages occur at the expense of muscovite, around veins which are close to the Mineralisation at Maldon is hosted in Early granite contact. The texture of quartz within Ordovician metasedimentary rocks which are the mineralised veins varies with distance from folded along parallel N-S axes. The folds are the contact. The truncation of veins and their upright and slightly overturned to the west, metamorphism by the granite, indicate that the with half wavelengths of about 230 m. The formation of auriferous veins predated the field is bounded to the north and west by the Upper Devonian granite intrusion. Vein Middle Devonian Harcourt Granite, which has minerals are unusually complex at Maldon, and metamorphosed the surrounding rocks to include pyrite, arsenopyrite, pyrrhotite, siliceous and aluminous hornfelses and rare loellingite, chalcopyrite, sphalerite, galena, calc-silicate rocks; and recrystallised vein molybdenite, scheelite, bismuth, rare quartz close to its contact with the granite. The bismuthinite, maldonite (Au3Bi), native Muckleford Fault, a major reverse fault with antimony and stibnite. Maldonite and the Bi, steep westerly dip, lies about 3-4 km east of the Mo and W bearing minerals only occur in the main reefs, with minor reefs (Muckleford auriferous quartz veins close to the granite Goldfield) lying between. (Hughes et al., 1997). It appears that mineralising fluids emanating from the The broad structural setting of the Maldon field intrusion have added these latter phases to the is similar to that of Bendigo. Shears with preexisting, regionally distributed, gold plus laminated quartz commonly lie sub-parallel to low sulphide mineralisation. bedding on the overturned western limbs of anticlines, and therefore dip steeply to the east Castlemaine-Chewton and Fryerstown (Ramsay & Willman, 1988; Morgan & Goldfields Woodland, 1990). The shears may cross the axial plane into the eastern limbs of the The geology and economic geology of the most anticlines, and there is maximum development productive parts of the Castlemaine and Fryers of quartz where the reefs transgress the Creek mining divisions have been thoroughly bedding ( Whiting & Bowen, 1976). The other described by Willman (1995). The following is a major type of reefs are “spurs” which dip east at brief summary of gold mineralisation in the 0-50° and commonly appear to be bedded. Castlemaine and nearby goldfield areas, which However, some spurs displace the vertical reefs, draws heavily on Willman's work. Rocks of the and they probably occupy faults lying sub- Castlemaine Supergoup are the host rocks for parallel to bedding. Ore is commonly found at the primary gold-quartz veins. They comprise points of flexure, or flattening of the dip. In turbiditic sandstone, siltstone, mudstone and places small, impersistent quartz veins or black carbonaceous shales which belong to a “spurries”, extend several metres outwards turbidite sequence of Lower Ordovician age. from the major shear-hosted veins. Spurries During the Benambran Deformation these associated with the Eaglehawk Reef formed an rocks were folded into a set of north-south 38 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

trending chevron folds with strong cleavage The Wattle Gully mine provides an excellent development and weak greenschist facies example of the interplay between strike metamorphism. The strongest gold-quartz faulting and folding; and associated mineralisation occurs in the eastern part of a mineralisation. Within the mined section, and regional anticlinorium with relatively at the lower levels, the west dipping Wattle symmetrical folds, which is bounded on the east Gully Fault zone runs parallel to bedding on the side by the major Shicer Gully Fault. This is western limb of an anticline. At higher levels, one of several unmineralised west-dipping it propagates across bedding on the eastern crustal scale faults in the Bendigo Zone, of limb (dilatant jog), but towards the surface and which the larger ones are presumed to extend near the axis of an adjacent syncline, it again at depth into a detachment zone beneath the becomes bedding-parallel (Fig. 8). The dilatant Ordovician rocks. Most of the gold deposits zone actually contains numerous, partly en occur within four narrow north-south trending echelon faults, commonly with associated zones (Willman, 1995) following the traces of extension veins. The faults contain laminated subsidiary faults, which may splay from the and massive quartz up to 2 m thick. Three Shicer Gully Fault at depth (Fig. 7). Gold separate dilatant jog complexes have been production was greatest in the easternmost observed to lie in an en echelon pattern with Chewton-Fryerstown zone and decreased in a increasing depth northwards. The structural westerly direction. controls on mineralisation at Wattle Gully have been studied in detail by Willman (1995) and Quartz veins formed progressively through Cox et al. (1995). various stages of deformation. In the early stages, flexural slip along bedding planes was Taradale - Malmsbury, Drummond North, accompanied by deposition of laminated quartz. Lauriston Goldfields Strike faults, which cross cut bedding, formed at a late stage as compressional structures with Reef mining in this area is characterised by reverse sense of slip, and are host to both workings on saddle reefs, and significant laminated and massive quartz. Sets of flat production came from inverted saddle or trough lying quartz veins ("spurs") formed in reefs. The reefs are hosted in tightly folded extensional fractures associated with the slates, sandstones and lesser siltstones of Lower development of strike faults. Strike fault and Ordovician age. Between 1860 and 1890, about extension veins are observed to cross cut the 50 individual mines were developed along four earlier bedding parallel veins. Most gold ore at main axial lines between Taradale and Castlemaine was located in west dipping strike Lauriston. The most productive zone was that faults and in "spurs". Bedding parallel veins held by the Russells group of companies, and saddle reefs were less important. Vein covering the north plunging part of Russells mineralogy is dominated by quartz, with minor Syncline, the adjacent anticline to the east, and carbonates, chlorite, white mica, albite and the Energetic Anticline to the west, near apatite. The major sulphide phases are pyrite Lauriston. In the Russells Reef Amalgamated and arsenopyrite, but sphalerite, galena, mine, six trough reefs were worked, the lowest chalcopyrite and pyrrhotite are also present. at a depth of about 378 m, and the longest was Wallrock alteration is typically weak. Chlorite proved for over 600 m along strike (John Taylor is present within 20 m of major veins, and & Sons, 1967). Notable occurrences of carbonate occurs within and immediately sulphides other than pyrite, are stibnite in the surrounding some veins. According to Cox et al. lower levels of the No.1 South Russells Mine, (1995) the highest gold grades at the Wattle and stibnite, sphalerite and galena in Gully mine tend to be localised in vein systems O'Connors Reef. that lie close to carbonaceous slates. They believe that a major factor in gold deposition To the west of the saddle reef belt, near has been mixing between metamorphic fluids Drummond North, is a group of "fissure" or from a deep source, and more reduced methane fault controlled reefs, which dip east at about bearing fluids produced during fluid reaction 60°-70° and which occur on the western limb of with black slates in the alteration zone. a north pitching anticline (Whiting & Bowen, 1976). The most important mines here were the O'Connors and Queens Birthday. Wallrock alteration extends up to a few metres on each GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 39

Figure 8 Cross section of Wattle Gully mine. 40 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

side of the veins and is reported in some cases Blackwood - Trentham Goldfield to have carried low grade gold mineralisation. The host rock lithology and structure for this Daylesford Goldfield area is similar to that for other goldfields to the north. Most of the auriferous reefs of Reef gold deposits at Daylesford are hosted in Blackwood are described as fissure reefs, but tightly folded Lower Ordovician slates and their characteristics in many mines, including sandstones with general NNW strike and fold the major Sultan, are poorly documented. wavelength ranging mainly from 60 to 400 m. These reefs strike approximately north-south, The controlling structures are predominantly sub parallel to the country rock. They appear west dipping reverse faults ("verticals") with to follow mainly west dipping reverse faults reef development restricted to the eastern limbs with major quartz development where the of the main anticlines (Baragwanath, 1953). faults transgress bedding. Spur veins, The most productive zones have been the presumably extensional vein arrays, are eastern limbs of three folds: the Ajax anticline prominent in these situations, for example on to the west of the field; the Rising Sun anticline the Annie Laurie and Grace Egerton Reefs. near the centre; and the Cornish anticline to The mineralised faults are displaced by east- the east. The fault reefs are comparable in southeast trending faults or "crosscourses" style to the "leather jacket" formations of (Ferguson, 1906). Ballarat East, or to the strike fault reefs of Wattle Gully. At Daylesford the faults strike at Most of the larger mines were confined to a about 330° (slightly oblique to bedding), dip at north-south belt about 5 km long and 2.5 km 50° to 70°W, and show dip slips up to 30 m. wide. The Sultan Reef line was the largest Several such faults were encountered in the producer, with mines extending to a depth of deeper workings, such as those of the Ajax about 270 m but averaging only about 60 m. mine, which reached a depth of 370 m. On Six parallel reefs were worked in the Sultan crossing from the eastern limbs of the anticlines Mine mainly above 230 m at which depth to the western limbs, the faults become bedded, mining was hindered by faults. Several with little or no quartz. Thus the major quartz companies worked profitably on the westerly growth has occurred within dilational jogs dipping fault-controlled Simmons Reef, mainly where the faults cut across bedding. In these above 76 m depth (Ramsay & Willman, 1988). zones the reefs may be up to 12 m thick, the A feature of the Yankee Reef line was the more massive ones comprising laminated to presence of saddle reefs, however most gold was massive quartz on one or both walls, enclosing a won from the legs of the uppermost saddle. mass of veined and brecciated country rock Stibnite has been recorded in several of the (Baragwanath, 1953). Favourable slate beds, mines in this district. like those of Ballarat East, appear to have had some influence on gold deposition. Mount Egerton - Gordon Goldfields

Flat reefs or spurs which formed in extensional These goldfields occupy a 12 km north-south arrays, were also a major source of gold at trending belt, with additional, isolated mines to Daylesford. They are sub-horizontal reefs the north of Gordon towards Bolwarrah which extend outwards from both the hanging (Roberts, 1984). The major mines of the Mount and footwalls of the "verticals". They are up to Egerton field, the Blackhorse, Egerton, Sister 2 m thick, and where well developed, as in the Rose and Rose all lie on the Egerton line of reef. Nuggety and North Nuggety Ajax mines, could This reef runs parallel to the strike of the be followed for 100 m across strike and 300 m enclosing Lower Ordovician rocks, has a steep along it. In addition to the Ajax line, large flat westerly to vertical dip, and is up to 20 m thick. reefs were present on Frenchmans and Its precise relationship to bedrock structure is Specimen Hill lines. Saddle reefs, although poorly documented, however subhorizontal numerous, were small and mostly quartz spurs (extensional veins?) intersect it, unproductive. "Counter reefs", which strike at suggesting that it may be controlled by a typical about 320° and dip at about 70° SW, commonly west dipping thrust. In places the spurs displaced the other reefs and formed the provided significant amounts of low grade ore boundaries to ore shoots. They were poorly (Bradford, 1903), and the main reef and auriferous, but some contained basic dyke rock. associated spurry quartz veins are exposed in open cuts south of Mount Egerton. A series of GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 41

Table 8 Major gold producers within the Melbourne Zone goldfields

Reef/mine Goldfield Production Grade (kg) (g/t)

Golden Dyke (Clonbinane) Sunday Creek 448 15 Doyles Reef Reedy Creek 356 125 Langridge Reef Reedy Creek 299 55 Providence Reef Yea 143 43 Ryans Reef Sunday Creek 118 24 Mundy Gully Reef Heathcote 65 11 Kilroys Reef Donnybrook 47 156 Welcome Reef Tea-Tree Creek 38 45 Empress of India Reef Reedy Creek 37 58 Balmers Reef Reedy Creek 33 41

(after Quarterly Reports of the Mining Surveyors and Registrars and Mines Department Annual Reports, 1864-1996 and Kenny, 1937a & b). east dipping faults have displaced the reef and were worked for gold in the late 1850s to the divided it into several south plunging blocks. A 1860s. Working was initially by means of feature of the goldfield is the presence of shafts up to 10 m deep, and later by large scale steeply dipping dykes, some of which are sluicing. associated with quartz reefs. The greatest producing mines at Mount Egerton were the Melbourne Zone Black Horse which produced 4,780 kg to a depth of 610 m, and the Egerton which A total of 1,863 kg of gold has been produced produced 5,680 kg to 534 m (Bowen, 1974). from the goldfields in the Melbourne Zone, with the bulk of gold derived from primary (reef) Several near vertical auriferous quartz reefs sources. Although recorded alluvial production occur near Gordon township, where the most was low, this is likely due to lack of records important mine, the Klondyke, reached a depth from the earliest period when much of the of about 128 m (Roberts, 1984). The Gordon surface gold was mined. Production from major Gold reef to the north was discovered in 1933 reef mines in these goldfields is shown in and yielded 937 kg of gold from a narrow, east Table 8. dipping reef (Ramsay & Willman, 1988). Total reef gold production from Mount Egerton- The history and geology of the goldfields within Gordon is estimated by Whiting & Bowen MELBOURNE are described below in order (1976) at 15,550 kg. Total reef and alluvial from west to east. production are estimated by Bradford (1903) at 22,400 kg from Mount Egerton and 4,600 kg Heathcote Goldfield from Gordon. Most of this goldfield, with the exceptions of the Other goldfields Mundy Gully and Tooborac areas, lies to the north of MELBOURNE, in HEATHCOTE Other, relatively minor goldfields lying to the (Edwards et al., in prep). The first gold south of Mount Egerton are the Mount Doran- discoveries in the area were made in 1853, with Elaine field and the Dollys Creek field. In the the original alluvial workings proving to be former area reefs follow a similar pattern to exceptionally rich (Flett, 1979). those further north, but most mines were less than 30 m deep. Gullies in the Mount Doran Gold was first found at Tooborac in the late Ranges were intensively worked for shallow 1850s (Flett, 1979) and the area saw alluvial gold (Roberts, 1984). At the Dollys intermittent activity into the 1890s, with a Creek Goldfield, high level Tertiary gravels minor revival in the 1930s (Howitt, 1933). A 42 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

1.3 kg nugget was found in Hayes Gully in 1870 quartz veins within the Cobaw granite (Kenny, and reefs graded over 150 g/t (Mundy Gully 1931). Goldfield Records in Garratt, 1990). Many reefs in the area contain abundant manganese Kilmore Goldfield oxide (Garratt, 1989). Gold was first discovered at Boundary Flat, The Mundy Gully area was worked from the Kilmore, in 1851. A subsequent discovery, at late 1850s through to the early years of the Prices Creek, about 7 km west-northwest of twentieth century and the reefs yielded an Kilmore, was worked from 1855 to the early average of over 13 g/t, presumably from hand- 1860s, producing gold from both alluvial and picked ore. The Mundy Gully Mine is located reef deposits (Flett, 1979). It is likely that the about 10 km south-southeast of Heathcote, with alluvial gold was derived from the Larry the associated alluvial workings further to the Bourkes Reef area to the south. Workings on south. Reef workings exceeded 70 m in depth Larry Bourkes Reef, which were active between and averaged over 10 g/t during production in 1864 and 1869, extended to a depth of 30 m and the early 1890s (Dunn, 1907d). Other mines a large area north of the reef was worked by between one and two km south of the Mundy open cut for detrital gold, presumably derived Gully Mine were worked to depths of up to from the reef (Flett, 1979; Dunn, 1907a). 30 m, and yielded gold at grades of up to 12 g/t. North-east of the reef a 40 m deep shaft was The reefs ranged in thickness from about 0.5 to sunk through basalt to access alluvial gold, and 1.2 m. alluvial gold with grades of up to 4 g/t was found in a palaeochannel of Kurkurac Creek The Mundy Gully workings are confined to the (Swensson, 1982). Other reefs in the area were immediate vicinity of the Mundy Gully worked to the mid 1900s (Dunn, 1907a). Anticline, with the main mineralisation being hosted by thick saddle reefs. Gold Larry Bourkes Reef, about 8 km west-northwest mineralisation is reported to increase to the of Kilmore, consists of a cemented sandstone/ north, and extend over a strike length of over mudstone fault breccia containing fine quartz 11 km. veins (Kenny, 1937d). The workings appear to be hosted by a bulge in the breccia zone, which A series of reefs striking approximately parallel ranges in width from 20 m to 50 m in the area to, and to the west of the Mundy Gully Reef between Rules Shaft and Hunts Shaft (Planet were also worked (Dunn, 1888; Garratt, 1990). Resources Group, 1976). Although old data indicated a grade of about 6 g/t gold, this Gold was also mined from quartz reefs in probably applied to selective rather than bulk granite (the Cobaw Granite), about 2.5 km mining grades, and more recent work suggests southwest of Tooborac. The main reef worked that the bulk grade is probably less than 0.2 g/t was the Sugar Loaf Reef, which had a strike of (Planet Resources Group, 1976). The area was 350°, dipped at 35° to the west, had a thickness apparently worked in the 1930s, but no of between 10 cm and 60 cm and was traced at production records for this period are available surface for over 400 m. The gold was reported (VandenBerg, 1992). to be very fine to subvisible, with a yield of about 30 g/t. Other quartz reefs hosted by The Goldie gold mine is located about 10 km granite were also worked in this area, including west of Kilmore and the mineralisation appears one thin reef which had grades of about 250 g/t to be associated with the axis of a minor gold. Reefs were worked to a depth of about anticline. The host rock is either a sandstone 25 m, which was the approximate depth to the (Dunn, 1907b) or mudstone (VandenBerg, 1992) watertable (Dunn, 1888). containing disseminated arsenopyrite. Gold occurs both in quartz veins and in the A quartz reef hosted by the Cobaw granite arsenopyrite, with concentrates of the latter about 5 km north of Lancefield was reported to grading at over 14 g/t gold (Dunn, 1907b). have yielded up to 125 g/t gold although later Workings extended to about 40 m depth and assays of this reef gave values of around 5 g/t, 100 m horizontally, with work in the 1930s which was more likely to have been typical. giving yields of over 13 g/t gold (Dunn, 1907b; Again, the gold from this reef was reported to VandenBerg, 1992). have been of very fine grain size. Similar fine gold was mined from alluvial deposits to the An occurrence of gold was reported from north, also presumed to have derived from Leydens Paddock Reef, about 2.5 km south of GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 43

Bylands. This occurrence was reported to have in a quartz reef which was worked to a depth of graded a few grams per tonne, and appeared to about 15 m. Exploration along the strike of the be associated with a minor anticline. The reef gave indications of gold mineralisation, but ferruginised quartz reef varied in thickness the quartz reef appeared to pinch out, being from a few centimetres to 0.6 m (Dunn, 1909). replaced by a narrow haematite vein. There is There is no record of gold production from this no record of production from this area (Stirling, site (VandenBerg, 1992). 1898)

An occurrence of gold was reported from Olivers Mt Piper Paddock, in the vicinity of the Kilmore diggings. The mineralisation appeared to be associated Mt. Piper and its vicinity does not have a with a fault traced over a distance of 60 m and history of gold production, and indications of striking 065°. The fault hosts a thin quartz past gold prospecting is restricted to a number reef, and a series of quartz stringers on its of shafts and adits in the area. However, there western side, both of which were auriferous, is a reported occurrence of stibnite from a vein although the mineralised zone did not appear to 30 cm wide southeast of Mt Piper and about extend to depth (Dunn, 1907c). The fault zone 1.5 km southwest of Broadford (Nicholas, 1884), consists of a strongly contorted and brecciated a location which lies on-trend with the Reedy sandstone with a quartz and limonite matrix Creek Anticline. (VandenBerg, 1992). The mineralisation at Mt Piper is hosted by Donnybrook Goldfield brecciated sandstone in a quartz veined matrix. The main breccia body trends parallel to the Gold was first discovered in this area in 1848, regional strike and is about 200 m long and with the first crushing yielding nearly 50 g/t 100 m wide. The breccia is extensively gold (Kenny, 1926). fractured, with most of the fractures trending parallel to strike, and dipping vertically to sub- A long, north-south striking quartz reef to the vertically. The mineralisation consists of west of Old Sydney Road, about 9 km north of pyrite, arsenopyrite, scorodite, cervantite and Mickleham was worked from 1852, in part by oxidised stibnite. Other breccia bodies in the open cut, and yielded over 120 g/t gold (Taylor, immediate vicinity show mineralisation 1862; Lidgey, 1897; Flett, 1979). A diorite dyke including arsenopyrite/scorodite and was reported to be associated with this line of berthierite, bismuthinite, silver-bearing reef (Kenny, 1930). This area was again tetrahedrite, gold, native bismuth and worked during the 1920s (Kenny, 1937a) which aurostibnite. Some minor tungsten appears to be the period of the most intense mineralisation was also noted. One diamond activity. The goldfield extends south into the drill hole in the breccia body averaged 48 m at Melbourne 1:100 000 map sheet area. 0.88 g/t Au, 11 ppm Ag, 3.0% As and 0.39% Sb from 184 m, including 7 m at 1.39 g/t Au from Workings at Woolfs and Kilroys mines on the 198 m. The highest gold assay was 1 m at 1.96 Kalkallo Reef extended to over 50 m depth and g/t Au from 243 m and the highest antimony horizontally over 120 m, with yields averaging assay was 1 m at 1.5% Sb from 172 m (BHP over 150 g/t gold, presumably from hand-picked Minerals Exploration, 1981). ore. The reefs ranged in thickness from 5 cm to 60 cm, dipped steeply to the east and were Sunday Creek Goldfield worked over a strike length of about 3.5 km. A second line of reef running parallel and to the Alluvial gold was found in Sunday Creek and east of the Kalkallo reef was also auriferous but the surrounding area prior to 1860. A gold- was not fully developed (Kenny, 1930, 1937a, bearing quartz reef was also found during this b & c). period but economic reef deposits were not developed until 1865 (Flett, 1979). Although A gold occurrence was reported from an area most of the activity in this goldfield was about 5 km north of Darraweit Guim, along confined to the previous century, there was strike and about half way between the some minor activity to the 1920s, with the Donnybrook and Kilmore Goldfields, apparently discovery of a 1.2 m wide zone of gold-bearing hosted by Deep Creek Siltstone (Stirling, 1898; quartz stringer in black slate in the bed of VandenBerg, 1992). Here gold was found in Stony Creek, about 3 km east of the Clonbinane small quantities in the nearby creeks, as well as mine (Kenny, 1928). 44 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

yielded several nuggets, the largest weighing Most of the gold workings on this field were over 4 kg (Murray, 1896; Meagher, 1864b). confined to mineralised quartz reefs within quartz porphyry dykes (Whitelaw, 1899a; The first quartz reef discovered, Langridge Zimmerman, 1967; Thomas, 1983). The main Reef, was worked from 1858 and was one of the dyke had a width of up to 25 m, and extended richest reefs in the area (Murray, 1884), over a length of about 5 km (Whitelaw, 1899a). producing over 340 kg of gold between 1859 and Originally considered to be a continuous body 1890 (Rech, 1986). Additional reefs were striking 080° (Whitelaw, 1899a), more recent quickly discovered (Flett, 1979), and were work has identified sections of the dyke which worked to the turn of the century. Reefs ranged appear to have been displaced due to faulting in thickness from about 10 to 30 cm with some between the Christina Mine at the western end exceeding 1.5 m, and grades ranged from 30 g/t of the dyke (Jenkins, 1900) and the Golden to 300 g/t (Murray, 1884; Kenny, 1932a) and Dyke and Apollo Mines in the east. A second occasionally exceeded 500 g/t (Rech, 1986). dyke striking parallel to and northeast of the Some of the 'reefs' on the Prince of Wales (also main dyke was also worked in the past known as the Golden Gate) line did not have (Thomas, 1981). extensive quartz vein development, but instead were characterised by local silicification and The dyke has undergone significant alteration, haematite veins (Kenny, 1932b). In some cases with alteration products including chlorite, country rock containing thin quartz stringers pyrite, leucoxene, calcite and epidote, and has around significant quartz reefs formed an been intensely weathered (Zimmerman, 1967). important component of the bulk ore. Gold mineralisation in carbonaceous shales was also The economically important mineralisation was reported (Forbes, 1898; Rech, 1986). confined to a series of 'pinch and swell' quartz reefs which strike perpendicular to the dyke Most mines were restricted to the shallow, high and occur at intervals of a few metres. The grade, oxidised zone above the local watertable, 'swell' portions of these reefs reach thicknesses but a few extended to depths of 150 to 180 m. of over 3.5 m and tend to be dominated by Thompsons Reef was accessed by a tunnel (the quartz, while the 'pinch' sections which narrow Long Tunnel Mine) over 200 m long (Forbes, to under 5 cm, tend to be dominated by stibnite, 1898; Rech, 1986). although the main reef in the Apollo Mine had large pods of stibnite ore within the 'swell' The reefs were mostly confined to the sections of the reef (Whitelaw, 1899a). The immediate vicinity of the Reedy Creek body of the dyke also contained disseminated Anticline, and most had a strike parallel to the sulphides including pyrite, arsenopyrite and anticline axis. This association of gold stibnite (Whitelaw, 1899a). Workings on this mineralisation and the axes of major anticlines dyke exceeded 100 m depth at the Apollo main in this area has been recognised since very shaft and horizontal workings reached 490 m in early times (Williams, 1964; Murray, 1884). the Golden Dyke mine (Baragwanath, 1939; O'Shea et al., 1992). In the southern part of this goldfield, quartz diorite dykes containing gold-bearing quartz Gold grades within the quartz veins ranged to veins were mined at the Aftermath gold mine 120 g/t and stibnite concentrations reached over on the Aftermath Dyke, and the Consols, 50%, while the dyke rock within zones of strong Leviathan, Golden Dyke and other mines on the alteration had gold grades of up to 6 g/t and Consols Dyke, with grades up to 31 g/t (Kenny, pyrite and stibnite were noted within sediments 1935; Rich, 1936; O'Shea et al., 1992; Rech, adjacent to the dyke (Zimmerman, 1967; Rech, 1986). 1986). Reedy Creek Goldfield Whittlesea Goldfield

Alluvial gold was discovered in Reedy Creek Gold was mined on the Whittlesea Goldfield, sometime after 1856 (Flett, 1979). Alluvial gold which extends from Glenvale to Morang, in the was mined actively to about 1860 but alluvial Melbourne 1:100 000 map sheet area, in 1860 mining went into decline until a revival in the (Flett, 1979). late 1860s (Meagher, 1866; Osborne, 1868). Nuggety Gully was particularly rich and Near the northern part of the goldfield, about 1 km northeast of what is now Eden Park, GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 45

Timms Reef yielded gold at grades of up to 90 g/t from a laminated quartz reef about 20 cm The Triangles Goldfield wide. The workings extended to 18 m depth and were active prior to 1899. The reef had a The first recorded gold workings on this field strike of 040° and a dip of 60° S (Whitelaw, was at the Triangle Lead on King Parrot Creek, 1899b; Bowen, 1959). This prospect appears to although gold was known from this area since have been worked in the 1930s (Bowen, 1959) 1851 (Flett, 1979). The Triangle Reef system, although grades for this latter period of activity also known as the King Parrot reefs, consisted are unknown. of three lines of reef which had been abandoned by 1864 (Meagher, 1864a). The Alluvial deposits from many of the creeks from mineralisation in the Triangles area is confined this area, especially Jacks Creek, produced gold to the crest and eastern limb of an anticline between the 1860s and the turn of the century, striking about 000°, and associated with a although some prospective areas could not be coarse sandstone unit 100 to 200 m thick, with developed fully due to their alienation during a stockwork quartz mineralisation in the lower period where property rights superseded those 4 m of this unit (Takoradi Gold NL, 1987). of miners (Whitelaw, 1899b). The alluvial deposits in creeks to the west of Yarra Creek, in About 6 km east of this area, around the vicinity of Mt Phillipa also produced gold Homewood, a number of workings were noted that may have been sourced from Timms Reef (Prowse & Finlay, 1988) which could not be and other quartz reefs in the vicinity traced in the historical record. The (Whitelaw, 1899b). mineralisation is confined to shears with a north-northwest trend, and recent channel and The mineralisation on this goldfield may be grab sampling showed grades of over 17 g/t related to the structurally favourable presence gold. Samples of a ferruginous sandstone at of the Whittlesea Anticline (Williams, 1964). Homewood Central gave grades of up to 1.4 g/t gold. Workings on the western flank of Strath Creek Goldfield Mt Charlotte extended over a strike length of 375 m, with mineralisation hosted by shear Reef mining commenced at Strath Creek in zones within interbedded sandstone and 1859 and an alluvial lead at a depth of 21 m siltstone. Samples of mullock gave grades of up was being mined towards the end of 1860 (Flett, to 0.52 g/t gold. Other workings were noted on 1979; Hill, 1860b). By the mid 1860s, reef Box Hill (Prowse & Finlay, 1988). mining was well established, with a tunnel of almost 100 m having been driven to access a Mt Robertson reef of up to 0.45 m thick, with grades approaching 200 g/t, by the Hayes Hill Gold This area contains a number of old workings, Mining Company, and other, shorter tunnels the most prominent of which is the Big Ben having been driven in the area to access reefs of Mine. This mine was established in 1946-47, similar dimensions (Meagher, 1866). and had significant development work, including a shaft and a 120 m adit. However, An investigation at the Don Maurice Mine (Bell, following the theft and destuction of mining 1965) described three gold-bearing reefs with equipment, the operation ceased. grades of up to 180 g/t. These reefs had been Mineralisation consists of subvisible to fine gold mined in the past, with workings probably and sulphides in a quartz veined fissure within exceeding 100 m horizontally, and around 15 m brecciated siltstone intruded by felsic dykes. in depth. The reefs strike 285°-290°, which is There is intense sericite alteration associated subparallel to bedding, and dip at 45°S to 52° S. with the best gold mineralisation, and The reefs are associated with north-dipping, carbonate (siderite) alteration and disseminated strike-parallel faults. The reefs contained pyrite in the general vicinity. Gold grades from stibnite, as well as pyrite and marcasite and rock chip samples in this area exceeded 12 g/t. were less than 10 cm wide. A concentrate of pyrite derived from slate near the reefs yielded About 800 m north of the Big Ben Mine, in an a grade of over 570 g/t gold. area known as Harrys Dyke, is a group of workings in a weathered felsic dyke several The mineralisation in this goldfield appears to metres wide. Average gold content was be related to the axes of the Strath Creek and estimated to be about 1 g/t, with mullock from Reedy Creek Anticlines (Williams, 1964). 46 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

the pits grading over 3 g/t (BHP Minerals matrix and appears to be most intense where Exploration, 1986). the quartz reefs intersect graphitic shales (Bessiere, 1971). This gold occurrence lies just to the east of the axis of the Reedy Creek Anticline (Williams, Ghin Ghin Goldfield 1964). The Ghin Ghin (Palestine Creek) Goldfield was King Parrot Creek Goldfield opened in 1867 (Flett, 1979).

Gold was known from the King Parrot Creek The field consists of a number of reefs and a since 1851, although official workings were not narrow alluvial deposit, over 1000 m long and opened until the late 1850s (Flett, 1979). up to 100 m wide (Cozens, 1985). The gold- bearing alluvium occurs along the course of Gold grades from reefs in this field tended to be Ghin Ghin Creek, just above its junction with low, generally less than 3 g/t, although grades the Goulburn River, about 8 km NW of Yea. of over 30 g/t were reported for individual The reefs from which the alluvial gold probably crushings (Kenny, 1921; Osborne, 1868; O'Shea originated (at least in part) are at the head of, et al., 1992). and to the east of Ghin Ghin Creek (Stirling, 1895), near the axis of the Yea Anticline. The mineralisation is confined to small Inconsistency between the size and grade of the horizontal quartz veins and stringers (Kenny, Ghin Ghin alluvial deposits and the relatively 1921) and appears to be associated with the modest reef deposits may indicate that axis of Strath Creek Anticline (Williams, 1964). additional gold may have been shed by a large, low grade zone of mineralisation in the area Tea Tree Creek Goldfield (Takoradi Gold NL, 1987).

Reef mining began at Junction Hill, at the head The alluvial deposits typically yielded from less of Tea Tree Creek in 1859, and alluvial gold than 1 g/t to around 30 g/t, although some rich was discovered elsewhere in Tea Tree Creek in patches were occasionally encountered 1860 (Flett, 1979), with grades of around 3.5 g/t (Stirling, 1895). (Hill, 1860a), although alluvial mining had ceased by the end of the year. A number of thin quartz reefs were also worked, including the City of Melbourne Reef Significant efforts went into the development of which was about 10 cm wide, had a strike underground workings on this goldfield, with a length of 1,600 m, dipped to the east and was tunnel being driven for a distance of over 230 m worked to a depth of 30 m. The gold from the in an attempt to intersect the Enniskillen Reef, reefs was very fine grained (Stirling, 1895; and workings reached depths of over 70 m Patterson, 1979). (Meagher, 1866). The Welcome Reef, southeast of Junction Hill, was also extensively The Providence and Red reefs are located less developed, with workings reaching a depth of than 100 m southwest of the City of Melbourne over 240 m (Lanzer, 1986; O'Shea et al., 1992). Reef and all strike about 140° (Whitelaw, The Old Mans Hope Reef, which averaged 1899c). McLeishs Reef, possibly an extension of about 15 g/t gold but had grades of 150 g/t at the City of Melbourne Reef yielded 23 g/t Au in the surface, contained significant accessory tests and shoots in the other reefs yielded up to stibnite (a vein up to 15 cm thick) which was 90 g/t Au (O'Shea et al., 1992; Stirling, 1895; regarded as an impediment to the effective Whitelaw, 1899c). recovery of gold (Whitelaw, 1899a). Grades approaching 300 g/t were recorded for this field, Gold has been found in thin ferruginous beds with quartz reef widths up to 4 m (Meagher, interbedded with black shales in the vicinity of 1866; O'Shea et al., 1992). the Ghin Ghin reefs. Samples of weathered bedrock in the area have been assayed, with the Mineralisation in this area appears to be highest grade recorded being 0.55 g/t Au related to proximity to strike faults (as at Old (Patterson, 1979). Mine Hill; Patterson, 1979) and is concentrated in the core of an anticlinal axis (O'Shea et al., Additional workings have been reported from 1992). Mineralisation consists of gold, stibnite, Quarry Hill, between the Ghin Ghin Goldfield cervantite and minor pyrite in quartz-shale and the Goulburn River, with channel and grab GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 47

sampling of the previously worked area yielding The most important occurrence of antimony in grades of up to 50 g/t gold (Prowse & Finlay, MELBOURNE is the Coimadai Antimony Mine, 1988). located about 15 km north-northeast of Bacchus Marsh. The deposit, first discovered in 1887, Yea Goldfield was initially described as a quartz reef ranging in thickness from a few centimetres up to 2.5 m, Gold was discovered at Yea in 1851, but the containing both disseminated and massive results of the early alluvial mining were stibnite from which some ore had been mined disappointing. There was a resurgence of (Murray, 1891). Subsequent work identified activity in the area about a decade later two separate reefs, Bodinsons Reef and (Flett, 1979). Drapers Reef. Bodinsons Reef which was on the north bank of Pyrites Creek and about 150 The largest mine on the Yea Goldfield was on m north of Drapers Reef, had a strike the Providence Reef, on the north side of the approximately 090° and dipped 60° north and Yea River, immediately north of Yea (Stirling, had an average stibnite content of 25%. 1947; O'Shea et al., 1992; Prowse & Finlay, Drapers Reef had a strike of 020° and dipped at 1988). This reef and associated structures 35° to the north and contained massive stibnite yielded an aggregate of over 930 kg of gold, with a thickness of between 45 cm and 75 cm. about two thirds of which came from the Feldspar porphyry dykes are associated with Providence lode. Workings on this deposit the deposit (Whitelaw, 1899a; Kenny, 1948; exceeded 100 m in depth and over 240 m Fisher, 1953; Bowen, 1970). The mine was horizontally (Wilson, undated; Sargant, 1934), operated by the Commonwealth Government and ceased due to inability to control inflow of during the 1940s. During this period a total of groundwater (Wilson, 1895; Bass, 1889). 4,300 t of low grade ore averaging 7.5% antimony was mined, whereas during the first Gold mineralisation is associated with shear period of activity between 1887 and 1915 over zones and breccia bodies near the axis of the 400 t of picked ore was produced (McLeod, Yea Anticline. The shear zones are sub-parallel 1966). to bedding and vary in thickness up to 0.6 m (O'Shea et al., 1992). The breccia zones consist Another major series of antimony deposits is of angular fragments of siltstone and weathered found at Clonbinane, about 13 km east of and/or rounded sandstone cobbles cemented by Kilmore, on the Sunday Creek Goldfield (see limonite, as in the Crystal breccia zone about p. 43). The stibnite is hosted by quartz reefs 1.5 km northwest of Yea (Kilpatrick, 1987). within two quartz porphyry dykes which strike This zone was previously described by Murray in parallel at 080°, and cut across the regional (1893) as an 'auriferous breccia' with grades of structural grain. The main dyke, which has a up to 20 g/t Au. The unit, which strikes width of up to 25 m, and extends over a strike northwest and is approximately 30 m wide, has length of about 5 km, is faulted in places and been traced along strike for 70 m (Takoradi discontinuous in outcrop. Gold NL, 1987) and is cut by occasional quartz veins. The Providence Reef itself was worked to Although most of the mining activity at these a depth of over 100 m and had grades of up to dykes was centred around gold, and the 180 g/t Au, but typically around 30 g/t Au presence of antimony was generally regarded as (Stirling, 1947; O'Shea et al., 1992). an impediment to its efficient extraction, the 3.3 Other metals Golden Dyke company crushed and sold small amounts of concentrates for their antimony Antimony content. Bulk stibnite concentrations of up to 25% were recorded during feasibility tests Antimony sulphide ores are prominent in the during the 1930s, although in places the Melbourne Zone and occur within quartz veins stibnite dominated portions of the host quartz and shear zones, as well as in disseminated reefs and probably approached 100% at these form in a number of dykes. These ores are localities. The body of the main dyke also regarded as epithermal (Hill, 1976) and form a contained disseminated stibnite, as well as distinct gold-antimony metallogenic province. other sulphides including pyrite and Antimony sulphide ores are also present to a arsenopyrite. (Baragwanath, 1939 & 1946; lesser degree within the Bendigo Zone, which Whitelaw, 1899a, Spencer-Jones, 1969). occupies the western portion of MELBOURNE. 48 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

Antimony ore grading 60% stibnite was reported about 3 km from Kilmore. No further Iron information is available on this occurrence (Baragwanath, 1946). Iron ore was mined and smelted at Lal Lal during the 1870s and 1880s. Production was North of Tyaak a stibnite dominated quartz reef low by modern standards (less than 2 tonnes (Cunninghams Lode) was worked for gold. iron per day), but satisfied local requirements Samples of the reef taken on the surface had during the period. The iron ore (buckshot stibnite concentrations of up to 10%. Most of gravel and tabular layers of limonite less than the stibnite was restricted to the footwall of the 2 m thick) was mined by open cut and reserves reef, with the antimony-rich section ranging in were estimated at 750,000 tonnes at 68% - 70% thickness from 10 - 15 cm. It was observed that iron oxide (Krause, 1877; Baragwanath, 1910a). the gold content increased with stibnite content A similar, but lower grade, deposit was mined at the western end of the reef, while the inverse by open cut at the Whipstick Scrub, about 5 km relationship was noted at the eastern end of the east of Mt Egerton (Baragwanath, 1910b; reef (Howitt, 1908; Hunter, 1908). Thomas, 1951). Other small, sub-economic deposits of limonite were reported near At Antimony Hill (Doogalook), about 10 km Coimadai (Jenkins, 1900) and near southwest of Yea, the Old Mans Hope Reef Barongarook (Kitson, 1906). contained stibnite veins up to 15 cm wide. The reef is very discontinuous and appears to be 3.4 Brown coal and peat mineralised only when cutting through graphitic shales. The nearby Welcome Reef was Coal also reported to contain stibnite, and copper and manganese minerals were reported as Brown coal (lignite) was discovered at Lal Lal accessories (Whitelaw, 1899; Bessiere, 1971; in 1857, during shaft sinking for gold Baragwanath, 1946). There is no record of exploration. Several additional shafts were stibnite production from this area. sunk, and the coal produced was shipped to Ballarat, Geelong and Melbourne. Minor Stibnite was reported from a vein about 20 km exploration and coal production continued southwest of Yea, but no additional details of sporadically in this area to 1919 (Preston, 1979; this occurrence were available (Bain & Ripper, 1975). Medwell, 1956). Brown coal was first discovered in the vicinity Stibnite was reported from an area about 6 km of Bacchus Marsh in 1884 during the south of Blackwood. This occurrence, the Black construction of a viaduct across the Werribee Hill antimony lode (also known as Murphys River. Sporadic exploration led to the Reef), consisted of a vein grading over 16% establishment of a short lived operation during stibnite, and ranging in thickness from 10 - the 1930s and to the establishment of the first 15 cm (Ferguson, 1906). economically viable operation, the Maddingley Brown Coal Mine, in 1944. This mine started Stibnite has also been mined from Belltopper as an underground operation and was later Hill, about 5 km west of Malmsbury, and the converted to open cut. Other brown coal mines Dry Diggings, Daylesford (Baragwanath, 1946). established in the general vicinity during this An occurrence was also reported from North period were ultimately acquired by the Drummond, southeast of Malmsbury (Kenny, Maddingley Company, which still operates a 1937e). major coal mine producing about 40,000 tpa of lignite which is used for fuel and as a soil Manganese conditioner. The mine is located on the southern outskirts of Bacchus Marsh (Ripper, Manganese mineralisation was noted about 3 1975; Edwards, 1990). km south of Mt William, within the Heathcote greenstone belt. The deposit consisted of two The brown coal unit at Bacchus Marsh is of parallel seams of manganese ore probably Early Miocene age and is a member of the hosted by the Mt William Metabasalt (Kenny, Werribee Formation. The thickness of the 1941; VandenBerg, 1992). The seams were Maddingley seam ranges from a few metres to between 30 cm and 60 cm thick and graded over 50 m, and it is very similar in its calorific value 40% Mn (Kenny, 1941). and other properties to the brown coal of the GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 49

Latrobe Valley. Recent production from this Buckley, 1995). A similar deposit was mine has been approximately 40,000 tpa. previously mined near Pyalong, although it Currently it is believed that there is may have been of lesser quality. This deposit approximately 60 million tonnes of consisted of a deeply weathered granite which economically winnable brown coal in the has been protected from erosion by a cover of vicinity of Bacchus Marsh, although other basalt and gravel (Keble & Watson, 1952). estimates using different parameters have given values for inferred reserves of up to 400 Secondary (transported) kaolin or ball clay has million tonnes of coal for the district (Edwards, been produced from the Lal Lal area prior to 1990). 1870, and from the Parwan Valley (Rowsley) and Darley areas since the turn of the century, Peat primarily from Werribee Formation sediments. Some of this material was used to produce A peat occurrence has been reported from a site firebricks for use in foundries, boilers and other 3 km east of Macedon, along Riddells Creek industrial applications although production (McHaffie & Buckley, 1995). geared to this industry declined with the decline of heavy industry and technological 3.5 Industrial minerals change. The quality of firebricks produced was regarded as superior to imported material, both Kaolin in durability and cost. Considerable quantities (of the order of 50,000 to 100,000 tpa) of clay, MELBOURNE has been an important source of mainly semi-ballclay, are still produced for high quality, primary (residual) kaolin since the brick and ceramic manufacture. There are turn of the century. Most of this has come from large potential reserves of this material, some the area between Gordon and Lal Lal, and of which is associated with fine-grained, high includes the major, but now closed operation at quality silica and minor lignite (Kitson, 1910; Mt Egerton. Most of the residual kaolin is Bell, 1959; McHaffie & Buckley, 1995; Olshina derived from deeply weathered, highly & Hiew, 1995). feldspathic dykes which are characterised by their low iron and low free silica content in the Diatomite weathered zone. The dykes are of variable thickness up to 4.5 m wide, and extend over Diatomite is a lightweight, friable sedimentary considerable distances - over 2,500 m at rock composed of siliceous shells of algae-like Mt Egerton. The clay is generally of very high organism called diatoms. It is used mostly as a quality, and consists of 98% kaolin. The only filter or filler and occurs most commonly in current operation in the area is the Stielow Victoria as thin interbeds with interflow Kaolin Mine (previously known as the Ceramic sediments associated with multiple flows of Kaolin Mine) at Lal Lal, which was first worked Newer Volcanic basalt. The basalt flows often in 1936, with reserves of over 500,000 tonnes. dammed the rivers, forming lakes suitable for The clay is suitable for various ceramic diatom growth. applications and as a filler (Kitson, 1905; Bain A deposit of diatomite was worked during the & Spencer-Jones, 1953; Bain & Knight, 1953; 1940s in Wedge Gully, west of Redesdale. The Kenny, 1942 & 1947; M. Stielow, pers. comm). diatomite was mined over an area of about 150 m by 50 m and had an average thickness of In addition to the kaolin derived from about 2 m. A total of about 400 tons was mined weathered dykes, a substantial resource of to 1950, with a maximum grade of 80% silica. kaolin has been identified in the weathered The workings were predominantly underground zone of a granodiorite body located a few and the diatomite was mined using room and kilometres north and west of Lal Lal and pillar methods. The deposit is sandwiched extending into BALLARAT to the west. The between two basalt flows and probably weathered zone averages over 5 m thick in the accumulated in a lake formed by the damming economically important areas. This deposit has of local drainage by the upper basalt flow been mined in the past, and has a proved and (Thomas, 1948; Crohn, 1952). probable reserve of over 3 million tonnes. The clay is exceptionally white, and is considered to Diatomite was mined near Newham, northeast be of high grade, suitable for paper filler, china of Woodend, from the 1920s to the 1950s, with a clay, refractory manufacture and general total of about 3,500 t produced during this ceramics applications (Ware, 1985; McHaffie & period. The grade ranged from 50% to over 80% 50 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

free silica. The diatomite was mined by lying beneath a cover of Newer Basalt, and is underground (room and pillar) methods over an probably derived from the weathering of the area of about 200 m by 60 m, and consisted of a basalt (Ferguson, 1920; Bain & Medwell, 1956). number of distinct seams of variable quality, with an aggregate thickness of about 7 m. As A minor occurrence of magnesite was reported with the deposit at Redesdale, this deposit is from a site about 3 km southwest of Maldon, also sandwiched between two basalt flows, and with 11 tonnes mined in the 1960s. Here the also probably formed by the damming of local magnesite forms a stockwork of nodular veins drainage by the upper flow (Howitt, 1925; in granodiorite (Nott, 1978). Crohn, 1952). Alunite The diatomite deposit at Moranding, about

10 km north-northwest of Kilmore, was also Alunite, K2Al6(OH)12(SO4)4, has been reported sandwiched between two basalt flows and as small nodules and mamillary crusts from produced 3,500 t during its period of activity Magnet Hill, about 1 km north of Gisborne over several decades to the 1950s. The deposit (Brough-Smyth, 1869). was worked using a combination of open cut and underground methods, with the thickness Phosphate of the diatomite varying up to about 7 m. Inferred resources at this site (as of 1950) were Phosphate minerals have been recorded in approximately 12,000 t (Crohn, 1952; McHaffie Ordovician black shale, slate and chert about & Buckley, 1995). 5 km east-northeast of Romsey (McHaffie & Buckley, 1995). Other minor diatomite occurrences have been reported from the vicinity of Lancefield, Gemstones Bacchus Marsh (underlying the basalts of the Bullengarook plateau and outcropping in the Gemstones, including agate, amethyst, valleys of Goodmans and Coimadai Creeks), emerald, garnet, peridot, quartz crystal, ruby, Daylesford and Broadford (Mahony, 1912; sapphire, topaz and zircon have been reported Crohn, 1952; Harris & Thomas, 1948; Crawford, from the Daylesford and Blackwood-Trentham 1940; Dickers Mining Record, 1864). areas. Many were found in both modern and ancient (deep lead) alluvial systems during gold Magnesite mining, and were collected from the mine dumps in the area. It is likely that the sources Magnesite has been found 5 km northwest of of the sapphire, ruby, peridot and zircon are Redesdale (Weston, 1992; Whitelaw, 1917; local basalts, while garnet, topaz, amethyst and Spencer-Jones, 1952). This occurrence has been other coloured quartz species derive from local known since the 1880s, but only two attempts granites and pegmatites (Stone, 1967; McHaffie at exploiting the deposit were made - the first & Buckley, 1995). There has been no prior to 1917 when 30 t of magnesite was mined commercial gemstone production from from an open cut about 3 km north of MELBOURNE. Redesdale, and the second in the early 1950s. At this location, the magnesite occurs as Feldspar lenticular bodies within a 400 m wide belt of slate and sandstone, approximately parallel to Feldspar was apparently quarried (prior to the strike, and not exceeding 3 to 5 m thickness. 1950s) from a small pegmatite body at a site The magnesite is exposed in gullies where the now flooded by the Lal Lal reservoir (Yates, Kimbolton Basalt overlying the Ordovician 1954; Roberts, 1984). Some coarse grained basement has been eroded. Its mode of origin is feldspar has been removed from a pegmatite unclear, but is possibly related to the vein about 6 km west of Maldon but the weathering of either the overlying basalt or occurrence was not regarded as economic basaltic dykes. (Nott, 1978).

Another occurrence of magnesite has been Limestone reported as outcropping on the east side of the Lerdederg River, north of Bacchus Marsh. This Magnesian limestone of Miocene-Pliocene age deposit consists of nodules of magnesite and was quarried from the Coimadai area, 8 km fine sand containing disseminated magnesite north-northeast of Bacchus Marsh. The GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 51

deposits, which consist of 45%-60% CaCO3 and Dimension Stone

30%-40% MgCO3, are up to 20 m thick and were used in the production of agricultural lime Dimension stone, including granite, sandstone, between 1875 and the 1980s. Most of the area basalt and slate, has been produced in is now inaccessible, following the flooding of MELBOURNE from the 1950s to the present Lake Merrimu (McHaffie & Buckley, 1995; day. Most of the material produced was used in Roberts, 1984; Officer & Hogg, 1897). Melbourne, although significant amounts were also used in other regional centres. Monazite The Harcourt Granite is one of the most Scattered occurrences of monazite were important and well-known sources of dimension recorded from a number of locations about 5 km stone in MELBOURNE. This granite has been northeast of Elphinstone, within the catchment quarried continuously since 1859, and has been of Granite Creek. The monazite was probably used extensively as a structural base for derived from the local granodiorite (McHaffie, buildings and as cladding. The granite is grey 1975). in colour and contains characteristic dark xenoliths. Grey granite from the southern part Extractive Industries of the Harcourt Batholith near Elphinstone has also been used in the past. The exact location of Extractive industries form the most the latter workings is unknown (Anon, 1937; economically important group of mineral King & Weston, 1997). Other dimension stone commodities produced in MELBOURNE, with operations utilising the Harcourt Granite are between 6.5 and 8.5 million tonnes quarried located in BENDIGO to the north. annually in recent years, and annual sales approaching $100 million, far in excess of all Granite from the Trawool Granite, about 10 km other commodities combined. Extractive southeast of Seymour, was used for ornamental industry resources include clay, sand, gravel work in the early 1990s. The rock did not take and hard rock consumed by the regional civil a durable polish, and has not been used since engineering and construction industries. Part this early period (King & Weston, 1997; of MELBOURNE falls within the Melbourne McHaffie & Buckley, 1995). Supply Area ( the major consumer of quarry products) and a detailed discussion of the Soft, fine-grained buff coloured sandstone of extractive industry and resources in this area is Permian age from Darley, north of Bacchus presented in Olshina & Jiricek, 1996. Marsh, and from Bald Hill, 3.5 km northwest of Bacchus Marsh was used to a minor extent in the past. It did not weather well, becoming soft and crumbly with time (O'Shea, 1978). Permian sandstone was also quarried from a site about 6 km west of Kyneton. The stone at this site was more durable than that from around Bacchus Marsh, but the quarries were flooded during the construction of the Lauriston Reservoir, and are no longer accessible.

A dark grey, porous, olivine basalt from a number of locations around Malmsbury was used extensively in the past for base courses of many Melbourne buildings, as well as in the vicinity of Kyneton. Material from this area was used to the late 1970s (King & Weston, 1997; Mines Department, 1937).

The best known variety of slate produced in MELBOURNE ("Castlemaine Stone") comes from an area about 5 km east of Castlemaine where it has been quarried from the 1850s to the present day. The slate is multicoloured, ranging from shades of orange and yellow, to 52 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

light and dark grey. It is mainly used for paving and cladding.

A quarry producing slate for minor domestic uses has recently opened near Ghin Ghin, about 9 km north of Yea. The slate ranges in colour from dark grey to dark green, with some red staining on the cleavage faces (King & Weston, 1997). Slate was quarried from several operations located about 9 km north of Bacchus Marsh. One operation in this area, near Coimadai, still produces small quantities of slate which is used for paving (King & Weston, 1997; K. Inan, pers comm). A number of slate quarries operated at Bullengarook, about 5 km west of Gisborne, from the late 1860s to the 1920s producing material for paving, roofing and other uses. Almost identical material was also quarried from an area about 6 km northwest of Gisborne between 1870 and the 1890s. This slate was dark grey, with pyrite mottling (King & Weston, 1997). GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 53

4 Geophysics magnetic but with underlying magnetic rocks probably greenstones.

4.1 Data The southern extent of the greenstones is overlain by Newer Volcanics. However, it can Detailed airborne magnetic, radiometric data be traced in the magnetic data to the southwest and digital terrain data are now available for to an isolated outcrop near Monegeeta. From the Castlemaine, Woodend, Yea and northern here it appears to swing around to the SSW half of the Bacchus Marsh 1:100 000 mapsheet towards Clarkefield. areas in central Victoria (Fig. 9). The data were obtained from two surveys flown during 1997 as In the central segment of the belt, immediately part of the Victorian Initiative for Minerals and north of the Cobaw Batholith, the greenstone Petroleum (VIMP). The Castlemaine, Woodend, belt is much narrower and mapped as andesites and northern half of the Bacchus Marsh area is and interbedded sediments (Edwards et al., covered by a fixed wing survey flown by World 1997) and has a weaker magnetic response. Geoscience. The Yea survey was flown by Geo Instruments using a helicopter with a boom Castlemaine Supergroup mounted magnetometer. The surveys have east-west flight lines with 200 m spacing and The Ordovician sediments are generally non- flying height of 80 m. magnetic but display narrow, linear (5-10 km strike length), weakly magnetic bands, assumed Willocks (1997) and McDonald (1997) have to be parallel to bedding but possibly parallel to prepared appraisal reports that provide a first cleavage. These linear units may be due to look at these surveys. The reports outline the pyrrhotite rich shales or previously survey operations, present images of the data at unrecognised volcanic units within the 1:250 000 scale and provide a discussion of the turbidites. regional geological features identified from the surveys. The Deep Creek Siltstone and Springfield Sandstone generally have a low magnetic Gravity data with a nominal station spacing response. The Calton Hill Sandstone Member 1.5 km is available over the Castlemaine and and Lintons Creek Conglomerate Member of north Bacchus Marsh 1:100 000 sheets (Steele the Springfield Sandstone have a distinctive et al, 1997a) and Woodend 1:100 000 sheet low radiometric response and a weak magnetic (Steele et al., 1997b). response and appear as long (5-20 km), thin, linear units which can be used as marker 4.2 Geological features horizons.

The intention of this section is to briefly The Muckleford Fault is apparent in the highlight the main features in the TMI image of radiometric and DTM data and also has a the new magnetic data (Fig. 9). The location of subtle expression in the magnetic data (Fig. 9). mineral occurrences is also shown on this Using the airborne data it can be extended figure. The previously listed reports provide a southward along strike from its currently more detailed appraisal of the geophysical data mapped position. The extension of the sets. Whitelaw Fault, mapped on the Bendigo 1:100 000 sheet to the north (Cherry and Heathcote Greenstone Belt Wilkinson 1994), cuts the southern margin of the Harcourt Granodiorite and extends to the The Heathcote Greenstone Belt has magnetic south. basalts, mapped as tholeiitic basalt, and interbedded non-magnetic volcanogenic Other discontinuities are evident in the sediments. Individual volcanic units can be magnetic data and are interpreted as faults. identified in the Mt William Volcanics, south of These faults have subtle magnetic responses the Cobaw Granite. Similar magnetic and are difficult to identify as they juxtapose responses on BENDIGO have been interpreted rocks with similar magnetic character. in Edwards et al. (1997) as a series of stacked Northwest and northeast trending faults are thrust sheets. The Knowsley East Formation also present. North-south strike ridges and and the Goldie Chert appear non- to weakly pervasive north-east and north-west fracture patterns can be identified in the DTM. 54 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

The Harcourt Granodiorite, Flowerdale Melbourne Zone Granodiorite and Mount Disappointment Granodiorite have a low magnetic responses The Kilmore Siltstone, Dargile Formation and and distinct contact metamorphic aureoles. The Melbourne Formation sediments are typically Mt Egerton Granite, Black Range Granodiorite non- to weakly magnetic with weakly to and Ingliston Granite are non magnetic. moderately magnetic NW trending marker beds. The Dargile Formation, north and east of Rhyodacite at Mt Macedon is mapped as one Kilmore, has a distinctive radiometric unit. However banding in the magnetic data signature, higher than that of the Deep Creek suggests that there may be several separate Siltstone and Springfield Sandstone. A flows. radiometric marker horizon is interpreted to show open folds and refolded folds. This folding Older Volcanics and Newer Volcanics cannot be seen in the magnetic data. Thin moderately magnetic units can be seen on the The Older Volcanics near Bacchus Marsh have limbs of the Limestone Creek Anticline. These a high magnetic (positive or negative) response. are either a basal unit in the Humevale Siltstone or an upper unit of the Melbourne The Newer Volcanics are complex features with Formation. high frequency and high positive or negative amplitudes. The basalts and the trachytic The Humevale Siltstone is the most extensive basalts have different radiometric responses. sedimentary unit in central YEA. These Some valley flows are evident. Individual flows sediments are generally northwest trending, can be distinguished from the radiometric data. weakly magnetic units and have high radiometric responses. Dendritic patterns in The source of the high amplitude magnetic the magnetic data, particularly well developed anomalies and coincident gravity high in this unit, possibly result from maghemite responses, north of Bacchus Marsh, is developed in palaeo or present drainage. unresolved. The trend direction is similar to trends on the northern margin of the Otway Folding and faulting can be identified in the Basin which were attributed by Pettifer et al. geophysical data. The most obvious fault occurs (1991) to be related to Australia- Antarctica in central YEA, along an axial trace, and has a rifting. It is suggested that these are basic low magnetic (where possible magnetite volcanics possibly associated with an aborted destruction has occurred) and a low radiometric rift. response. This fault trends northwest for approximately 17 km and deviates from the mapped axial trace only in the north. Other faults coincident with axial traces are also apparent on YEA (McDonald, 1997).

Granites

The Strathbogie Batholith has a low magnetic response with a distinct change of magnetic character between the granite the adjacent sediments. A separate, deep, highly magnetic intrusion is interpreted to lie beneath the Strathbogie Batholith. This high magnetic response does not correlate with the mapped Strathbogie Batholith.

The Cobaw Granite has a low magnetic response and is clearly defined by the change of magnetic character between the granite and its contact metamorphic aureole. Zoning in the granite is very obvious in the radiometric data (Willocks, 1997). GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 55

5 Mineral resource potential successful in many cases. Examples in and around MELBOURNE are the Bendigo , and prospectivity Maldon, Fosterville, Heathcote and Bailieston goldfields. Gold mineralisation in complex 5.1 Gold networks of subsidiary veins, breccia zones and in sedimentary host rocks, together with that along major, well defined reef lines, is capable Historically, gold has been the most important of sustaining large scale, open pit mining. metallic mineral commodity of interest to Significantly, this situation applies to the explorers in central Victoria, however target western part of the Melbourne Zone, with types have changed somewhat over the years. relatively low historical gold production, as well Prior to the 1980s, the search for primary gold as to the Bendigo Zone. It applies both to was mainly focused upon the well known relatively late stage gold mineralisation (with narrow vein styles of mineralisation, which stibnite association, and possibly linked to felsic were only amenable to mining by underground magmatism and the Tabberabbera methods. During the 1980s, large tonnage, low Deformation) and to older gold mineralisation grade deposits which could be mined by open (with typical pyrite, arsenopyrite, galena, cut as well as underground methods, became sphalerite association, and possibly linked to attractive targets. This was due mainly to the Benambran Deformation). increases in gold prices, and advances in mining and metallurgical processing Gold deposits of the two zones have been techniques. Thus the target types were characterised by Gao and Kwak (1995) who extended to include gold in complex quartz vein suggest that the following features would be systems, in places along major shears; useful in exploration: disseminated gold hosted in sedimentary rock, in places associated with mafic to intermediate Au-As type deposits (Bendigo Zone) volcanic rock; and gold in porphyry/epithermal systems associated with granitoids. 1. domal structures of the Early Ordovician Investigations of alluvial gold prospects have turbidites - the first order control in locating continued throughout the period of modern ore deposits; exploration, with a recent resurgence of interest in deep lead gold, and in primary gold lying 2. reverse faults in domes, particularly the beneath the lead systems. connections of concordant and discordant faults that created dilation jogs; Vein systems of the Bendigo Goldfield type, 3. bedding concordant and discordant particularly those incorporating saddle and structures in the domal crests that hosted associated leg reefs, remain as attractive, large saddle veins; scale targets (Sharpe & MacGeehan, 1990). This is due to the great continuity of reefs (up 4. brecciation of large veins and occurrence of to several kilometres) along anticlinal axes, the recrystallised clear quartz in association repetition of saddles with depth in anticlinal with arsenopyrite, pyrite, galena and axes, and the relatively high grade of the reefs. sphalerite; There is clearly scope for discovery of gold 5. veins that have a contact with carbonaceous orebodies of this, and other styles, not only in slates; areas of high historical production, but in other areas where similar structural and geochemical 6. arsenopyrite alteration and carbonate conditions have prevailed. Exploration would spotting in wall rock; benefit from an enhanced understanding of the 7. haloes of Au, As, S, and CO in slates; and types of fold and fault geometry, operative 2 stress regimes and ore fluid-wallrock 8. low Sb/As ratio in arsenopyrite. interactions that are conducive to gold deposition. On a regional scale, airborne Au-Sb type deposits (Melbourne Zone) magnetometry can assist in the search for favourable structural settings, both in areas of 1. N-S or E-W domal structures of the Silurian- Palaeozoic outcrop and beneath shallow cover. Devonian turbidites;

The reassessment of historical mining centres 2. reverse faults and quartz veins in the domes; in recent years, as possible hosts for bulk faults not necessarily parallel to axial tonnage, low grade gold orebodies has been planes; 56 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

3. brecciation of sandstones by hydraulic BENDIGO) is of this type. The mineralisation, fracturing, and quartz vein stockworks in which in the sulphide zone may include the domes; carbonates, sericite, pyrite, arsenopyrite and stibnite in addition to the gold, occurs between 4. carbonate spotting, silicification, and argillic sedimentary quartz grains at the expense of alteration; plagioclase and other matrix materials. 5. occurrence of stibnite in veins and in Alteration is intense near faults and shear wallrocks; zones where gold grades tend to be higher, and may form haloes up to 150 m from major 6. haloes of Au, Sb, S, and CO ; 2 structures (Kwak & Roberts, 1996). It typically 7. Au-Sb correlation in rocks and soils; and includes carbonates (calcite, siderite, sideroplesite and ankerite), sericite, chlorite 8. high Sb/As ratio in arsenopyrite. and sulphides (pyrite, chalcopyrite and sphalerite). Silicification is generally absent. Although clearly defined, broad domal In the oxide zone, gold has commonly been structures are not as common in the Melbourne remobilised and dispersed into zones that are Zone in the eastern portion of MELBOURNE as wider than those containing the original they are in BENDIGO to the north, there may sulphide mineralisation. Carbonate contents be a weak association between known gold may be depressed by weathering, and the gold deposits and domal culminations. There is a is associated with limonite. Apart from much stronger association between proximity to favourable structure and lithology, recognition anticlinal axes in general and gold deposits, of characteristic alteration minerals and with most of the known deposits occurring on or bedrock geochemistry may be useful exploration near anticlinal axes. In addition to the above, tools. Elevated values for gold (Au>100 ppb) there also appears to be an association between and arsenic (As>100 ppm) in bedrock may be gold mineralisation and the following features: indicators of this type of mineralisation. Infrared spectrometry shows promise as a tool 1. in tense limonitisation; for mapping alteration haloes around gold 2. carbonaceous shales, especially where these orebodies of the above type. Use of a Portable are intesected by faults; and Infrared Mineral Analyser (PIMA) on samples from across the alteration zone of the 3. the presence of dykes, usually feldspar Fosterville orebody in BENDIGO has shown a porphyry. very good correlation between the distribution of gold and alteration-related illite (Merry & It is not clear whether the latter is a function of Pontual, 1996). direct association between the presence of dykes and mineralisation, or whether such Modern geophysical techniques may also be dykes are ubiquitous through the area, and are used in identifying areas of enhanced only remarked upon where noted near gold prospectivity. deposits. The presence of dissemniated sulphides in the large dykes of the Sunday The goldmines in the Castlemaine goldfield Creek Goldfield would make such dykes a good plotted over the first vertical derivative and exploration target using geophysical methods, automatic gain control images of the TMI data since their surface expression is generally poor. show some weak north-south trends (<2 nT) coincident with the mines. It is likely that this The association of massive, brittle sandstones association is a combination of geological and carbonaceous shales in close proximity to information and artifacts produced from the anticlinal axes would also make an attractive gridding of the magnetic data. target, with fractures within such sandstones providing loci for concentrations of gold For instance, shallow workings on the east side mineralisation. of the Irish Anticline are coincident with a weak magnetic high (<2 nT). Whereas 400 m to Fine grained gold hosted in sandstone, siltstone the west, the mines along the mapped Eureka or greywacke has been highlighted as a Fault and Emu Fault (Willman, 1995) have no relatively new type of exploration target by distinct magnetic expression, and if anything Kwak & Roberts (1996) and Hughes et al. appear to be coincident with magnetic lows. (1997). A proportion of the ore at Fosterville, The weak trends may be due to pyrrhotite in Nagambie, Bailieston and Bendigo (all in shales. Forward modelling by Whitehead GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH 57

(1996), for Ordovician rocks in the Ballarat traverses or a high resolution airborne survey area, found that a susceptibility contrast of (eg. line spacing 50 m) is required for detailed 10 x 10-5 SI was sufficient to produce a 2-3 nT prospect exploration and evaluation. anomaly. Data from detailed gravity traverses (50 m In contrast, data aliasing is introduced into the stations) across deep leads are being used in the data during the gridding process. These are Ballarat, Creswick and Clunes areas to model perpendicular to the flight lines, trending the basement topography and map the deep north-south, i.e. the same as the strike leads beneath basalt or Tertiary cover. This direction. Clearly, the trends from geological technique could be applied to map the deep sources need to be separated and the aliasing leads around Daylesford, and Malmsbury and minimised. the Goulburn River.

The goldfields on YEA generally occur on or 5.2 Non metallics near anticlinal axes. Folds, anticlinal axes and faulted anticlinal axes are clearly seen in the The basalts and the trachytic basalts have magnetic and radiometric data which may be different radiometric responses. The responses, used to determine along-strike extensions of the which are a useful geological and regolith goldfields. mapping tool, can be used to distinguish individual flows. It may be possible to establish Porphyry dykes, possibly originating from a correlation between the radiometric signature magnetic granites and associated with gold and basalts with a preferred composition. This mineralisation, are noted on YEA. process may be useful to highlight areas to target for quarry materials. Exploration approaches using these data for gold might include

· enhancing the magnetic data using 1VD, AGC and other filters to identify associations between the magnetic responses of rock units and structures in mineralised areas and use them to target areas along strike

· identifying dilation jogs possibly favourable for mineralisation

· analysis of the located profile data as part of detailed geological interpretation

· designing a filter for the magnetic data to determine areas of thinner basalt and focus on underlying prospective areas within the bedrock

· a program to measure rock susceptibilities from fresh rock to determine the magnetic contrasts between the target units and use these data to model magnetic responses from detailed ground traverses

· map 'favourable' rock units using the radiometric data, for example, altered dykes · analysis of the digital terrain model to identify cross cutting structures

The new VIMP data are best used for regional exploration and prospect generation. Prior to drilling, more detailed data either from ground 58 GEOLOGY AND PROSPECTIVITY - CASTLEMAINE, WOODEND, YEA, BACCHUS MARSH

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