The giant Kalgoorlie Gold Field revisited

The Neoarchaean Kalgoorlie Gold Field contains the giant Golden Mile and world-class Mt Charlotte deposits, which have been the subject of much research for over 100 years. The Golden Mile deposit is a complex array of ductile to brittle vein and breccia lodes that are predominantly hosted in the highly-fractionated Golden Mile Dolerite sill. The Fimiston lodes comprise an array of narrow lodes that evolved broadly syn- to late-formation of the regional D2 NW-trending foliation. The lodes are characterized by pyrite veinlets and disseminations, quartz veinlets and breccias, and banded quartz-carbonate veins with sericite, carbonate, and pyrite-dominated alteration. Bonanza Green-Leader, or Oroya-style, lodes, with grades in excess of 1000 g/t Au, are similar to the Fimiston-style lodes, but are characterized by abundant visible gold, native tellurium and more abundant telluride minerals within roscoelite-bearing alteration zones. The arguably structurally younger Mt Charlotte-style lodes are characterized by a pipe-shaped, coarse-grained quartz, carbonate and scheelite vein-stockwork with distinct vertically-zoned, carbonate-sericite-albite-pyrite ± pyrrhotite dominant alteration assemblages around veins within Unit 8 of the Golden Mile dolerite and porphyry dykes. The network of steep- and gently-dipping extension and shear fracture-fill veins are associated with NE-trending fault sets that cross cut the regional NW-trend. The deposit area is intruded by swarms of porphyry dykes, including syn-volcanic mafic dykes, early and volumetrically most significant c. 2.67 Ga feldspar-phyric porphyry dykes, as well as later c. 2.66‒2.65 Ga calc-alkaline hornblende-phyric dykes associated with younger c. 2.65‒2.64 Ga lamprophyre dykes. All post-volcanic dykes have similar orientations to the Fimiston lodes. The feldspar dykes are clearly overprinted by all styles of mineralization, although the relationship between hornblende-phyric and lamprophyre dykes and gold mineralization is more ambiguous. Most agree that gold mineralization was post-peak regional metamorphism of host rocks, although its relative structural timing is controversial.