Mineralogy and In Situ S Isotope Systematics of Replacement-Type Sulphides from the Wolverine Volcanogenic Massive Sulphide (VMS) Deposit, Yukon, Canada

The sediment-rich Wolverine volcanogenic massive sulphide (VMS) deposit, Yukon, Canada, shows evidence of both exhalative and replacement-type mineralization. Locally, replacement-type sulphides are exquisitely preserved, replacing hanging wall shales in a bed-by-bed manner and exhibiting well-developed mineralogical, textural, mineral assemblage, and sulphur isotope zonation. At the top of mineralization, replacement-type sulphides are predominantly framboidal to colloform pyrite-sphalerite-galena and partly replace framboidal pyrite in hanging wall shales. With depth in the massive sulphides pyrite becomes more recrystallized, with pyrite changing from colloform to spongy and sheet like to euhedral to rounded. Furthermore, there is a decrease in sphalerite and galena coupled with an increase in pyrite, chalcopyrite, and pyrrhotite towards the base of massive sulphide. Sulphur isotopes range from delta S-34(V-CDT) =-27.4 to +14.3 per mil, but are generally more negative near the top of mineralization in replacement-type sulphides, and are more positive and have restricted ranges near the base of mineralization (e.g., delta S-34(V-CDT) = +10.6 to +14.3 per mil). These ranges in delta S-34(V-CDT) are consistent with sulphur derived from both bacterial sulphate reduction (BSR) and thermochemical sulphate reduction (TSR) of seawater sulphate. Paragenetic and spatial relationships argue that early mineralization was dominated by mixing of hydrothermal fluids with BSR-derived sulphur, whereas later (higher temperature) sulphides were dominated by sulphur derived from TSR.