Major's Creek,N.S.W., Australia — A Devonian epithermal gold deposit

Mineralized veins at Major's Creek consist of preponderant quartz and carbonate gangue with gold, Au-Ag tellurides and base metal sulphides within silicified and sericitized dykes or granodiorite of the Braidwood Granite. Fluid inclusion studies indicate deposition throughout the range 350–80°C by low salinity fluids. Significant Au-Ag telluride mineralization took place at a temperature of about 155°C. Mineral deposition was due to the separation of a liquid CO₂ phase from an originally CO₂-rich aqueous fluid. Observed argillic alteration is a consequence of acid leaching above the boiling zone. Mineralization is epithermal in character and probably formed during the existence of a hydrothermal convective system. A relationship with similar epithermal gold deposits in the adjacent Eden-Yalwal Rift zone is inferred.