TRACE ELEMENT CHEMISTRY OF SILICATES AND OXIDES AS VECTORS TO METAMORPHOSED SEDIMENT-HOSTED PB-ZN-AG AND CU-AU DEPOSITS IN THE CAMBRIAN KANMANTOO GROUP, SOUTH AUSTRALIA

The stratiform and syngenetic Wheal Ellen, Angas, Scott’s Creek, Aclare, Strathalbyn, and St. Ives Pb-Zn-Ag deposits, and the enigmatic Kanmantoo Cu-Au deposit, occur in metamorphosed (amphibolite facies) siliciclastic sedimentary rocks of the Tapanappa Formation in the Kanmantoo Group. These deposits are hosted in a regional, stratabound, metamorphosed hydrothermal alteration zone consisting of garnet-andalusite-biotite±staurolite schist. Metallic minerals in the Pb-Zn-Ag deposits consist of sphalerite, pyrite, galena, chalcopyrite, pyrrhotite, arsenopyrite, and sulfosalts. The Kanmantoo deposit is characterized by discordant and pipe-like orebodies (Kavanagh and Spitfire), and concordant mineralization (Nugent) spatially associated with meta-exhalative rocks. The metallic minerals consist of chalcopyrite, pyrrhotite, magnetite, Bi minerals, and pyrite.

Although Fe-rich garnet is common in country rock mica schists in the Kanmantoo Group and in altered rocks spatially associated with most Cu-Au deposits at Kanmantoo, the composition of garnet is more Mn-rich with proximity to Pb-Zn-Ag mineralization, and the Nugent orebody. Furthermore, the Zn concentration of garnet associated with Zn-Pb-Ag mineralization is high (100 to 252 ppm Zn) relative to that spatially associated with the Kanmantoo Cu-Au deposit and the country rocks (<26 ppm Zn). The Zn and Mn contents of staurolite are also high (up to 5.6 wt. % ZnO and up to ~5,000 ppm Mn) relative to those associated with staurolite in the Kanmantoo deposit (up to 1.3 wt. % ZnO and 600 ppm Mn). Biotite in Pb-Zn-Ag deposits occurrences are enriched in various elements including up to 2,600 ppm Mn, 6,400 ppm Cu, and 1,200 ppm Zn in the St. Ives deposit, and up to 1,200 ppm Zn, 5,400 ppm Mn, and 5 wt. % Tl in the Angas deposit. These elemental concentrations are in contrast to those associated with biotite in the Kanmantoo deposit (< 200 ppm MnO and ZnO, and <2 ppm Tl). Like staurolite and gahnite, ilmenite at St. Ives is Zn-rich and contains up to 22.9 wt. % ZnO. The enrichment of certain metals in oxides and silicates in Pb-Zn-Ag and Cu-Au deposits relative to those found in the same minerals in unaltered country rocks, and positive Eu anomalies for garnet in ore, constitute potential pathfinders to base metal deposits in the Kanmantoo Group.