Metal leaching and inorganic sulfate reduction in volcanic-hosted massive sulfide mineral systems: Evidence from the paleo-Archean Panorama district,Western Australia

Comprehensive studies of the well-preserved, paleo-Archean (3.6-3.2 Ga) Pan orama volcanic-hosted massive sulfide district of Western Australia provide compelling evidence that metals were leached from the base of the volcanic pile and redeposited at its top in volcanic-hosted massive sulfide deposit s. This leaching provided more than enough metal to form known deposits, im plying that direct magmatic input of metal is not required. Sulfur depletion from the base of the volcanic pile was associated with an increase in Fe2O3/FeO and hematitic alteration. These data, combined with s ulfur isotope data, indicate that seawater sulfate reduction was facilitate d by the oxidation of rock FeO to hematite at high temperature in the H2S s tability field. This is the first time that seawater sulfate reduction has been demonstrated regionally in an ancient volcanic-hosted massive sulfide mineral system. The data presented here require paleo-Archean seawater to b e sulfate bearing.