Re-Os DATING OF SULFIDES ASSOCIATED WITH GOLD MINERALIZATION IN CENTRAL VICTORIA, AUSTRALIA

We report Re-Os isotope ages that are the first for sulfides closely associated with gold mineralization at the Bendigo and Maldon goldfields in central Victoria. Two arsenopyrite samples from Bendigo contain 11 ppb Re and 0.08 ppb highly radiogenic Os (LLHR samples; Stein et al., 2000) and have model ages of 444 ± 7 and 447 ± 7 Ma, with a mean model age of 446 ± 5 Ma. A five-point isochron based on these arsenopyrite analyses plus three pyrite analyses, including one replicate, gives an age of 438 ± 6 Ma. Molybdenite associated with Au, Te, Cu, and Sb mineralization at Maldon gives an Re-Os age of 376 ± 2 Ma, similar to the age of the nearby Har-court Granite. These results support previous 40 Ar/ 39 Ar data indicating that initial emplacement of gold mineralization in central Victoria occurred in the Late Ordovician, during the earliest stages of accretionary development of the southern Lachlan fold belt. The molybdenite data are also consistent with the mobilization and/or introduction of gold during Late Devonian magmatism.