Geochemical and stable isotope studies of the No. 4 lode, Kalgoorlie, Western Australia

The no. 4 lode is a silicified, pyritic shear zone with gold telluride mineralization which is located in the Golden Mile dolerite along the western limb of the Kalgoorlie syncline. Wallrocks in this zone have undergone a series of metamorphic and metasomatic events. This alteration is characterized by an increase in the KO/NaO ratio, introduction of CO and S, and significant enrichment of Au, Ag, Te and other ore-forming constituents. Major- and trace-element and isotopic data are presented (40 chemical analyses). Ore mineralization is thought to have formed by reaction of chloritic host rocks with a moderately-reduced, near-neutral hydrothermal fluid at T 250 + or - 50oC. Isotope and geochemical data suggest that these ore fluids were of metamorphic derivation and may have incorporated magmatic C, S, and possibly precious metals at deeper levels in the crust.- J.E.S.