Stable isotope and geochemical evidence for genesis of secondary copper deposits at Girilambone, New South Wales, Australia

Abstract The Girilambone copper deposit of New South Wales, Australia, serves as an end-member model for development a classic oxidation-zone profile in environment virtually free both the effects active tectonics and significant fluctuation local water table. oxidation zone other deposits may be interpreted history recently tectonics, palaeoclimate, water-table stability by comparison to deposit. Unlike profiles porphyry western North America, which have been overprinted many fluctuations produced appears little modification original profile. Oxidation primary sulfides at was exothermic process facilitated chemolithotrophic bacteria, recorded malachite oxygen isotope thermometry estimates up 52°C, very light carbon values. bacteria generated CO 2 migrated upwards react with rich meteoric fluids vadose precipitate malachite. America experienced recent tectonic activity, secondary minerals (clays, iron oxides carbonates) were not repeatedly fractured offset during re-establish permeability. This reduced permeability slowed release from system, producing significantly elevated partial pressure , sufficient azurite formation dominate. Azurite values indicate lower temperatures 32°C, less bacterial activity than sulfide-digesting relatively seasonal swings population, does interbanded typical episodic populations triggered precipitation. Thus absence Cu-carbonate banding palaeoclimate indicator. Deeper zone, native cuprite dominate, whereas chalcocite formed enrichment blanket just above modern Oxygen pseudomorphs after that these retrograde reaction when production digestion waned near ambient. In post mining environment, chloride-rich groundwater seeps actively atacamite, while exposed remnants sulfide masses form outer rind porous Exceptions this sequence occur due localised fluid channelisation perched lenses mineralogical overprints.