Proterozoic tectonic framework and metal deposits of southwestern Australia

Abstract

Abstract The Proterozoic tectonic evolution and metal deposits of southwestern Australia reflect a dynamic history of repeated aggregation and dispersal of continental fragments. This contrasts with previous interpretations that much of Australia was part of a Proterozoic supercontinent in which all orogenic activity and metallogenesis was ensialic. Southwestern Australia contains a wide range of sedimentary and intrusive rocks that span the whole of Proterozoic time. They occur in four Proterozoic orogens and as cover sequences on one of the orogens and on an adjacent Archaean craton. Each Proterozoic orogen formed during one of three episodes of continental collision, which occurred in the Early, Middle and Late Proterozoic. The oldest deposits (Hamersley Group) occur on the Archaean Pilbara Craton and are dominated by banded iron formations containing major supergene enriched hematite-goethite ores. Following Early Proterozoic rifting, the Archaean Pilbara and Yilgarn cratons collided and amalgamated forming the intervening Capricorn Orogen between 2.0 and 1.6 Ga. Granite with associated minor Mo, W, Bi, Pb and U mineralisation is abundant in the vicinity of the suture. Sedimentary rocks from passive continental margins and foreland basins, together with basalt, gabbro and serpentinite from oceanic or arc environments were folded and thrust outwards onto the margins of the adjacent cratons, and locally contain prominent Au, Cu and Pb mineralisation. Middle Proterozoic sedimentary rocks (Bangemall Group) that unconformably overlie the Capricorn Orogen contain significant deposits of PbCuAg and Mn. The Middle Proterozoic Albany-Fraser Orogen is dominated by huge thrust sheets of high-grade gneiss and granite reflecting another episode of continental collision along the southern margin of Western Australia. Exposed Proterozoic rocks of the Pinjarra Orogen are high-grade gneiss and granite that appear to have been involved in Late Proterozoic continental collision. The Paterson Orogen comprises Early, Middle and Late Proterozoic components that were also involved in Late Proterozoic continental collision. It contains major deposits of AuCu, CuPbZn and U.