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-Arehean (3.6-3.2 Ga) Panorama volcanic-hosted massive sulfide district of Western Australla provide compelling evidence that metals were leached from the hase of the volcanic pile and redeposited at its top in volcanic-hosted massive sulfide deposits. This leaching provided more than enough metal to form known deposits, implying 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 sulfur isotope data, indicate that seawater sulfate reduction was facilitated by the olddation of rock FeO to hematite at high temperature in the H2S stability 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 pah-Archean seawater to be sufate bearing.