A regional scale Fixed-Wing TDEM survey of the Palaeo-Proterozoic Bryah Basin, Western Australia: Providing insights into a setting highly prospective for VMS Cu-Au and mesothermal Au Systems

Abstract

The Bryah Basin is part of the Capricorn Orogen, a collision zone between the Archaean Pilbara and Yilgarn Cratons in western Australia . It was formed during back-arc sea-floor spreading and rifting on the northern margin of the Yilgarn Craton, and contains a succession of mafic and ultramafic rocks of mid-oceanic ridge basalt to oceanic plateau affinity, overlain by clastic and chemical sedimentary rocks. The Basin is host to significant mineralisation, including mesothermal orogenic gold, coppergold volcanogenic massive sulphides (e. g. DeGrussa). The regolith of the region is complex and varied, and although well mapped, a more complete understanding of this variability has remained undetermined except at very local scales. In June 2012, CSIRO in collaboration with GSWA, flew a reconnaissance, regional scale, airborne SPECTREM AEM survey over the Bryah Basin at a line spacing of 5500 m. The data were inverted using a smooth model layered earth inversion, with the GA-LEI algorithm. The data show that the Basin is characterised by a regolith that exceeds 150m in depth in places. The most dominant regolith features are associated with sediment filled palaeovalleys, valleys that underlie the current track of the Murchison and Gascoyne Rivers and their tributaries. The orientation of the palaeovalleys are show indicates a strong lithostructural control. The regional regolith framework defined from the AEM data provides a basis for better understanding and interpreting the regolith geochemistry that has been acquired across the Basin. The AEM data also indicate the presence of several strong basement conductors that lithologically related. The survey further demonstrates the value of regional AEM surveys in the pre-competative data suite.