In the St. Ives gold camp in the Yilgarn Craton of Western Australia, several stages of hydrothermal alteration are pre-dating (epidote-calcite-magnetite 1-pyrite 1-chalcopyrite-quartz), synchronous with (plagioclase-carbonate-pyrite 1±Au±magnetite 2±hematite) and post-dating (quartz vein system-pyrite 2-chlorite) gold mineralization. Hydrothermal fluids are characterized throughout the alteration history to gain an in depth understanding of chemical processes which controlled gold precipitation and the site of gold ore bodies.
Hydrothermal fluids in the camp evolve over time from low salinity aqueous, to low salinity a queous-carbonic to carbonic followed by late stage saline aqueous-carbonic. The fluids show broadly and increase in CO
, salinity and decrease in temperature with time. Importantly, during gold mineralization, hydrothermal fluids show rapid salinity decrease and CO
increase as monitored in syn-gold, growth-zoned carbonate grains.