Mineralization, alteration assemblages and stable isotopes of the intermediate-sulfidation epithermal Strauss Deposit, Drake Goldfield, North-Eastern NSW, Australia

The intermediate-sulfidation epithermal Strauss deposit is part of the Drake Goldfield of north-eastern NSW, Australia. The mineralization is gold dominant with minor silver and significant zinc, copper and lead. Strauss has a combined total resource of 2.66 Mt @ 1.5 g/T Au and 1.9 g/T Ag. Petrographic analysis has shown the deposit to be hosted by varying layers of dacitic ash flow tuffs and a cross-cutting lamprophyre dyke though previous authors classified some of the tuffs as intrusive andesites. Mineralization mainly occurs in the form of vein stockworks of three main orientations. Structural analysis indicates that these resulted from two fault system events and one conjugate fault system. Petrographic and SEM analysis shows that there are two different mineralization styles, a pyrite dominant and chalcopyrite dominant assemblage, with three main mineralization events. Correlation analysis for the assay data indicates that Au has a strong relationship with Ag and a moderate correlation with Pb. XRD analysis indicates widespread argillic-phyllic and propylitic alteration. Silver tellurides have been found as late-stage grains associated with the chalcopyrite mineralization assemblage. Sr shows a significant depletion due to the intense and pervasive alteration at Strauss. The carbon and oxygen isotopes of the vein carbonates suggests that the carbon from the late-stage carbonates was derived from a magmatic source with a significant input of low temperature meteoric water, while the sulfur isotopes indicate a magmatic sulfur source.