Oxidized gold deposits and Cu-Au skarns in the Eastern Goldfields Superterrane, Western Australia: Structural setting and space-time relations to I-type intrusions

Hematite-bearing biotite/sericite gold deposits and epidote skarns in greenstones of the 2.7 Ga Eastern Goldfields Superterrane are associated with monzodiorite-tonalite and monzonite-syenite intrusions. Older thrust and strike-slip faults were reactivated and mineralised during late-orogenic magmatic activity. At Granny Smith (37 t Au) in the Laverton district, a monzodiorite stock (2665 +/- 3 Ma) cuts across D1 folds and D1 thrusts in greywacke. Biotite-sericite lodes formed at 2660 +/- 5 Ma when renewed reverse faulting (D3) fractured the stock. At the nearby Wallaby deposit (180 t Au), monzonite-syenite dykes intruded a 600m-wide pipe of conglomerate-hosted epidote Fe skarn (2662 +/- 3 Ma). Intrusion-related Au-Ag veins cut the skarn at dike contacts. Reverse faults (D3) cut the skarn and veins and contain sericite lodes dated at 2650 +/- 6 Ma. Deposits in the Kalgoorlie district are controlled by strike-slip faults. The Golden Mile (1500 t Au) comprises D2 sinistral shear zones and minor D3 thrusts displacing D1 folds in meta-dolerite. Porphyry emplacement and sericitic alteration occurred during the transition from D2 to D3. At Mt Charlotte (125 t Au), D3 thrusts are offset by D4 dextral strike-slip faults controlling quartz-veined ore (2655 +/- 13 Ma) in meta-dolerite. Epidote Fe-Cu-Au skarns and associated sericite Cu-Au lodes occur at Mt Shea near Kalgoorlie, where D3 thrusts displace monzodiorites (2658 +/- 3 Ma) of an unroofed intrusive complex.