Mineralisation, alteration assemblages, geochemistry and stable isotopes of the low-sulfidation epithermal Strauss deposit, Drake Goldfield, north-eastern NSW, Australia

Abstract

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