Camp- to deposit-scale zonation of hydrothermal alteration in the St Ives gold camp, Yilgam Craton, Western Australia: evidence for two fluid systems?

摘要

Hydrothermal sulphide-oxide-gold mineral assemblages in gold deposits in the Archean St. Ives gold camp in the Norseman-Wiluna greenstone belt in Western Australia indicate extremely variable re-dox conditions during hydrothermal alteration and gold mineralization. Reduced alteration assemblages occur in deposits in the southwest of the camp (e.g., Argo, Junction), and moderately oxidized to oxidized assemblages occur in the northeast (e.g., North Orchin, Revenge). Hydrothermal magnetite, which is spatially associated with distinct lows in detailed gravity, pre-dates gold-associated chlorite-carbonate-biotite-pyrite alteration. The spatial distribution and temporal sequence of sulphide-oxide-gold assemblages indicate either a progressive change in redox conditions of one hydrothermal fluid, or more likely, the presence of two spatially restricted hydrothermal fluids with variable redox states.