Oxygen isotope mapping in the Panorama VMS district, Pilbara Craton, Western Australia: applications to estimating temperatures of alteration and to exploration

Whole rock oxygen isotope data are presented for the Panorama district, in the Archean Pilbara Craton of Western Australia, where near-perfect exposur e reveals a cross section through a complete volcanogenic massive sulfide ( VMS) hydrothermal alteration system. The delta O-18 values decrease with de pth in the volcanic pile, across semi-conformable alteration zones, to valu es below 6 parts per thousand immediately above a large (180 km(2)) subvolc anic intrusion have lower delta O-18 values (6-8 parts per thousand) than l east altered granite (8 parts per thousand), apart from sericite-quartz alt ered zones, which are slightly higher (8-10 parts per thousand). Corridors of low delta O-18 values crosscut this regional zonation, and are coinciden t with transgressive feldspar-destructive alteration zones, which underlie VMS mineralization. The whole rock oxygen isotope distribution patterns are interpreted to represent alteration temperature, where high delta O-18 val ues correspond to low temperature alteration and low delta O-18 values corr espond to high temperature alteration. Alteration temperatures, which were calculated using modal alteration mineral abundances and an assumed fluid d elta O-18, are consistent with this interpretation. Increasing temperatures with depth in the volcanic pile and high temperatures in transgressive cor ridors leading up to VMS deposits, are consistent with a convective hydroth ermal model, in which heat from the subvolcanic intrusion drove seawater th rough the volcanic pile Granite-hosted sericite-quartz alteration zones are O-18-enriched. and are tentatively interpreted to have formed from a mixed magmatic-evolved seawater fluid.