The Wilga base-precious metals deposit, Benambra, Victoria, Australia |
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| Authors: | R Cox GB Ebsworth DL Forsythe |
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| Institution: | Roy Cox &Associates, Westleigh, NSW 2120, Australia |
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| Abstract: | Wilga is one of several Au-bearing volcanogenic massive sulphide deposits localized within Silurian felsic volcanics of the Lachlan Fold Belt of NE Victoria. Exploration has delineated a resource of 3.7 Mt averaging 3.4% Cu, 5.5% Zn, 0.4% Pb, 31 g/t Ag and 0.5 g/t Au within a lensoid-shaped sulphide body which strikes NE, dips NW and occurs at a depth of 50–160 m below surface. This body has maximum dimensions of 470 m strike, 350 m down-dip and 37 m true width delineated by 59 surface diamond drill holes and an exploration adit with 40 underground diamond drill holes. There are two main types of mineralization: Stratiform massive sulphides , (mainly pyrite, low-Fe sphalerite, variable chalcopyrite and minor galena with very minor silica/dolomite gangue) and Stratiform chloritic sulphides (mainly chalcopyrite, with subordinate pyrite and sphalerite, in a gangue of chlorite and minor dolomite). The deposit is layered with at least 6 distinct stratigraphic horizons/cycles of mineralization each characterized by a Cu-rich base and Pb-(Zn)-Au-As-rich top. Facies variations are locally rapid. Economically the deposit consists of 3 sub-lenses of roughly equal tonnage: a Cu-rich central lens of Chloritic Sulphides (av. 5.9% Cu, 3.6% Zn, 0.3% Pb, 32 g/t Ag and 0.2 g/t Au) between upper and lower lenses of Zn-rich Massive Sulphides (av. 1.8% Cu, 6.7% Zn, 0.5% Pb, 31 g/t Ag and 0.7 g/t Au). Gold mineralization, locally up to 7 g/t over 6 m, shows a strong spatial association with Pb, (Zn) and As in pyritic massive sulphides. |
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