Date of Award
Master of Science
Geological and Atmospheric Sciences
The synsedimentary Wheal Ellen, Angas, Scotts Creek, Aclare, Strathalbyn, and St. Ives Pb-Zn-Ag-(Cu-Au) deposits occur in metamorphosed (amphibolite facies) siliciclastic sedimentary rocks of the Tapanappa Formation in the Kanmantoo Group, South Australia. These deposits are hosted in a regional, stratabound, metamorphosed hydrothermal alteration zone consisting of garnet-andalusite-biotite±staurolite schist. This alteration zone and meta-exhalative rocks, consisting mainly of iron formation, spessartine garnet-quartz rocks, quartz-magnetite rocks, and quartz-gahnite rocks, serve as the major pathfinders to Pb-Zn-Ag-(Cu-Au) deposits, which consist of sphalerite, pyrite, galena, chalcopyrite, and pyrrhotite, with minor arsenopyrite and sulfosalts. Compositional variations in ferromagnesian silicates and oxides can also be used as guides to ore on a more local scale. Although Fe-rich garnet is common in country rock mica schists in the Kanmantoo Group, the composition of garnet is more Mn-rich with proximity to Pb-Zn-Ag-(Cu-Au) mineralization. Furthermore, the Zn concentration of garnet associated with Pb-Zn-Ag-(Cu-Au) mineralization is high (100 to 535 ppm Zn) relative to the country rocks (<26 ppm Zn), and to that spatially associated with the Kanmantoo Cu-Au deposit, which is the largest Cu-Au deposit in the Tapanappa Formation. The Zn and Mn contents of staurolite associated with Pb-Zn-Ag-(Cu-Au) mineralization 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) and in quartz-mica schists. Biotite in the Pb-Zn-Ag-(Cu-Au) deposits 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, up to 4,079 ppm Zn, and 6,687 ppm Mn in the Wheal Ellen deposit, and up to 1,200 ppm Zn, 5,400 ppm Mn, and 3.9 wt% Tl in the Angas deposit. These elemental concentrations are more elevated than those in biotite associated with the Kanmantoo deposit (< 200 ppm MnO and ZnO, and <6 ppm Tl) and in country rock quartz-mica schists. Like staurolite and gahnite, Mn-bearing ilmenite at St. Ives is Zn-rich and contains up to 23 wt% ZnO. The enrichment of certain metals in oxides and silicates in Pb-Zn-Ag-(Cu-Au) deposits relative to those found in the same minerals in unaltered country rocks constitute potential pathfinders to base metal deposits in the Kanmantoo Group, and to metamorphosed SEDEX deposits elsewhere.
Tott, Katherine, "Ferromagnesian silicates and oxides as vectors to metamorphosed sediment-hosted Pb-Zn-Ag-(Cu-Au) deposits in the Cambrian Kanmantoo Group, South Australia" (2018). Graduate Theses and Dissertations. 17338.