This section provides a brief overview of the earth resources of the Tasman Fold Belt System in Victoria. Metallic mineralisation is subdivided into eight styles based on genesis and setting. Nonmetallics form a large part of the Palaeozoic earth resources of Victoria. The following summary is given in chronological order except for orogenic gold and magmatic– hydrothermal deposits which are grouped.
Cambrian tholeiite–boninite volcanism
Boninite is thought to be the source of metal for Victoria's main orogenic gold deposits, while sulphide-rich seafloor volcanic-associated mineralisation in tholeiitic sequences may have been critical in preconcentrating gold. The richest of these subeconomic deposits, Mount Ararat south of Stawell, contains 1 Mt @ 2.7% copper, 9 g/t silver and 0.6 g/t gold.
Cambrian calc-alkaline volcanism
A few base and precious metal deposits occur within calc-alkaline volcanic sequences—possible equivalents of Tasmania's Mount Read Volcanics. Preliminary studies indicate a spectrum of deposit styles ranging from seafloor volcanic-associated to magmatic–hydrothermal.
Cambrian Moralana Supergroup
Small gossans in the Moralana Supergroup containing silver–lead ± gold ± copper were worked in the late 1800s on Nolan Creek. Like many deposits in the Kanmantoo Group, mineralisation appears to have early stratabound elements related to lithological boundaries which have been modified by metamorphism and deformation.
Orogenic gold
Most of Victoria's gold has come from orogenic gold deposits in the Lachlan Fold Belt. Total production to June 1998 is about 2500 t. Mineralisation is chiefly associated with structurally controlled quartz veins in deformed lower Palaeozoic sedimentary rocks. Gold production is unevenly distributed and deposits tend to change in structural character and/or mineral assemblage from one zone to the next.
Three main periods of mineralisation have been defined by radiometric dating and geological relationships, broadly correlating with the late stages of the three orogenies—Benambran, Bindian and Tabberabberan. The Bindian Orogeny has not been recognised in western Victoria but mineralisation of this age is present.
Cambrian tholeiite–boninite volcanism
Boninite is thought to be the source of metal for Victoria's main orogenic gold deposits, while sulphide-rich seafloor volcanic-associated mineralisation in tholeiitic sequences may have been critical in preconcentrating gold. The richest of these subeconomic deposits, Mount Ararat south of Stawell, contains 1 Mt @ 2.7% copper, 9 g/t silver and 0.6 g/t gold.
Cambrian calc-alkaline volcanism
A few base and precious metal deposits occur within calc-alkaline volcanic sequences—possible equivalents of Tasmania's Mount Read Volcanics. Preliminary studies indicate a spectrum of deposit styles ranging from seafloor volcanic-associated to magmatic–hydrothermal.
Cambrian Moralana Supergroup
Small gossans in the Moralana Supergroup containing silver–lead ± gold ± copper were worked in the late 1800s on Nolan Creek. Like many deposits in the Kanmantoo Group, mineralisation appears to have early stratabound elements related to lithological boundaries which have been modified by metamorphism and deformation.
Orogenic gold
Most of Victoria's gold has come from orogenic gold deposits in the Lachlan Fold Belt. Total production to June 1998 is about 2500 t. Mineralisation is chiefly associated with structurally controlled quartz veins in deformed lower Palaeozoic sedimentary rocks. Gold production is unevenly distributed and deposits tend to change in structural character and/or mineral assemblage from one zone to the next.
Three main periods of mineralisation have been defined by radiometric dating and geological relationships, broadly correlating with the late stages of the three orogenies—Benambran, Bindian and Tabberabberan. The Bindian Orogeny has not been recognised in western Victoria but mineralisation of this age is present.
Auriferous qtz-vein (crack-seal) from Bendigo. Approximately 7cm thick. Picture courtesy of S.A. Vollgger
Late Silurian Cowombat Rift
The Cowombat Rift contains a complex suite of (poly-)metallic deposits. The most important are the Wilga and Currawong seafloor volcanic-associated deposits hosted by the Gibson Folly Formation of the Limestone Creek Graben. Mining of the Wilga deposit produced 34 037 t copper, 16 894 t zinc and 10 136 kg silver between 1992 and 1995.
The Cowombat Rift contains a complex suite of (poly-)metallic deposits. The most important are the Wilga and Currawong seafloor volcanic-associated deposits hosted by the Gibson Folly Formation of the Limestone Creek Graben. Mining of the Wilga deposit produced 34 037 t copper, 16 894 t zinc and 10 136 kg silver between 1992 and 1995.
Early Devonian rifts, basins and cauldrons
Early Devonian extensional tectonic settings in the Benambra Terrane contain the Stateís most diverse suite of syngenetic and epigenetic deposits, although these are mostly small. Intermittent base and precious metal production commenced in 1865. The most important setting is the Buchan Rift where deposits show a strong relationship with extensional faults which appear to have acted as conduits for ore fluids.
Late Devonian Mansfield Group and Combyingbar Formation
The Upper Devonian Mansfield Group and Combyingbar Formation contain small amounts of red-bed copper, uranium, vanadium and silver concentrated at redox and pH boundaries.
Magmatism
While there is no current mining, modest amounts of tin, gold, molybdenum and tungsten have been mined from magmatic–hydrothermal deposits dating back to the late 1800s. Noteworthy molybdenum deposits occur in all zones except the Deddick Zone and the Central Victorian Magmatic Province. Major tin ± gold-bearing granites and dykes are confined to the Tabberabbera and Omeo zones. Granites with tungsten ± molybdenum ± tin mineralisation are widespread, occurring in all Lachlan Fold Belt basement terranes. Small amounts of gold were mined from porphyry deposits in Boggy Plain Supersuite granite in the Benambra Terrane, while porphyry copper ± molybdenum deposits fringing Lower Devonian extensional settings are subeconomic. Granite mineralisation is strongly linked with magma chemistry; and hence composition of the crust and tectonic setting. Minor gold–antimony mineralisation accompanies Middle to Late Devonian high-level magmatism.
Early Devonian extensional tectonic settings in the Benambra Terrane contain the Stateís most diverse suite of syngenetic and epigenetic deposits, although these are mostly small. Intermittent base and precious metal production commenced in 1865. The most important setting is the Buchan Rift where deposits show a strong relationship with extensional faults which appear to have acted as conduits for ore fluids.
Late Devonian Mansfield Group and Combyingbar Formation
The Upper Devonian Mansfield Group and Combyingbar Formation contain small amounts of red-bed copper, uranium, vanadium and silver concentrated at redox and pH boundaries.
Magmatism
While there is no current mining, modest amounts of tin, gold, molybdenum and tungsten have been mined from magmatic–hydrothermal deposits dating back to the late 1800s. Noteworthy molybdenum deposits occur in all zones except the Deddick Zone and the Central Victorian Magmatic Province. Major tin ± gold-bearing granites and dykes are confined to the Tabberabbera and Omeo zones. Granites with tungsten ± molybdenum ± tin mineralisation are widespread, occurring in all Lachlan Fold Belt basement terranes. Small amounts of gold were mined from porphyry deposits in Boggy Plain Supersuite granite in the Benambra Terrane, while porphyry copper ± molybdenum deposits fringing Lower Devonian extensional settings are subeconomic. Granite mineralisation is strongly linked with magma chemistry; and hence composition of the crust and tectonic setting. Minor gold–antimony mineralisation accompanies Middle to Late Devonian high-level magmatism.
