SHRIMP S-isotope evidence for fluid mixing during gold mineralization in a slate-belt gold deposit (Hill End, New South Wales, Australia)

Sensitive high-resolution ion microprobe (SHRIMP) sulfur isotope data show that pyrrhotite, pyrite, galena and chalcopyrite in syntectonic auriferous quartz veins at the Hill End goldfield are characterized by two populations, with δ34Sfluid-values of ∼ +7 and ∼0%. These two populations are accounted for by fluid mixing involving two sources of sulfur during evolution of the vein systems. A local sulfur source and reduced fluids derived from trough-fill Siluro-Devonian sedimentary and volcano-sedimentary sequences are responsible for the first two gold-bearing events, whereas a more oxidized fluid and a sulfur source from turbidites and volcanics in deeper parts of the crustal sequences appear responsible for gold deposition late in the second gold-forming event and are the dominant influences in the final gold-forming stage. For fine-grained mixtures, where mineral separation is difficult, the SHRIMP analyses are particularly useful for tracing detailed δ34S variations of sulfides precipitated in different paragenetic stages.