Date of Award
Master of Science
Geological and Atmospheric Sciences
Paul G. Spry
Multiply deformed sediments of the Cambrian Kanmantoo Group, which were metamorphosed to the amphibolite facies, host numerous Cu-Au, Fe-S, and Pb-Zn-Ag deposits, of which the largest is the Kanmantoo Cu-Au deposit (34.5 Mt @ 0.6% Cu and 0.1 g/t Au). Mineralization at Kanmantoo is characterized by discordant and pipe-like orebodies (Kavanagh and Emily Star) along with mineralization concordant to bedding (Nugent) that is spatially related to meta-exhalative rocks. Previous studies have suggested a syngenetic origin for the Pb-Zn-Ag and Fe-S deposits, whereas the Kanmantoo deposit remains controversial, with syngenetic, metamorphogenic, and post-peak metamorphic models being applied. The stratiform nature of the Nugent orebody at Kanmantoo, along with the recognition of a zone of chalcopyrite-magnetite-rich rocks at the syngenetic Wheal Ellen Pb-Zn-Ag deposit, which shows a metallic mineral assemblage almost identical to the most common assemblage at Kanmantoo, supports a genetic link between the Pb-Zn-Ag deposits and Cu-Au mineralization, and is consistent with a metamorphosed syngenetic model for Cu-Au mineralization. The discordant nature of most orebodies at Kanmantoo is the result of varying degrees of syndeformational remobilization that is associated with syn- to post-peak metamorphism. Major and trace element compositions, coupled with principal component analysis, show that the compositions of garnet, biotite, staurolite, chlorite, muscovite, and magnetite in metamorphosed altered rocks at Kanmantoo can be distinguished from those, where present, in metamorphosed country rocks (i.e., metapsammites and metapelites). Garnet, chlorite, biotite, and muscovite in quartz garnetite within quartz mica schist associated with the Nugent orebody are elevated in Mn (up to 19.5 wt. % MnO - garnet, 2825 ppm - chlorite, 3206 ppm - biotite, and 108 ppm - muscovite) and Zn (up to 170 ppm - garnet, 1602 ppm - chlorite, 1592 ppm - biotite, and 108 ppm - muscovite) relative to samples in other orebodies and in unmineralized rocks elsewhere in the Kanmantoo Group. Such enrichments in these elements mimic similar enrichments in the same minerals in metamorphosed altered rocks associated with Pb-Zn-Ag deposits in the Kanmantoo Group. Biotite in metamorphosed altered rocks at Kanmantoo contains elevated concentrations of Pb (up to 110 ppm), and, in general, Zn (up to 841 ppm), whereas muscovite is also elevated in Pb, Zn, and Cu (up to 272 ppm Pb, 77.6 ppm Zn, and 173 ppm Cu). Staurolite in these same rocks contains up to 1.6 wt. % ZnO and is considerably more enriched in Zn than in unaltered country rocks (~0.1 wt. % Zn). The trace element enrichments in silicates studied here constitutes a potential pathfinder to metamorphosed Cu-Au mineralization in the Kanmantoo Group and emphasizes the geochemical and genetic links between the Pb-Zn-Ag and Cu-Au deposits.
Meaghan Victoria MacPherson
MacPherson, Meaghan Victoria, "The origin of the sediment-hosted Kanmantoo Cu-Au deposit, South Australia: Mineralogical considerations" (2017). Graduate Theses and Dissertations. 17736.