Increasing prospectivity in a covered terrain – the southern Thomson Orogen, northwestern NSW

Abstract

The Southern Thomson Project aims to advance understanding of tectonic history and mineral prospectivity of basement rocks of the southern Thomson Orogen beneath extensive Mesozoic and Cenozoic cover. The project area in northwestern New South Wales (NSW) and western Queensland is considered underexplored, with poor definition of structural corridors and mineral systems in the Palaeozoic rocks. This collaborative project between Geoscience Australia, the Geological Survey of New South Wales (GSNSW) and the Geological Survey of Queensland is acquiring and interpreting new geoscience data, including geophysical, geochemical, and isotopic investigations. Geophysical data interpretations and models have been tested through a program of stratigraphic drilling to provide basement cores for studies of petrology, geochronology, geochemistry, petrophysics and mineral systems. Downhole geophysical logging of the drillholes also aims to characterise the cover sequences and define depth to basement. Interpretation of regional aeromagnetic and gravity data and synthesis of existing mineral, water-bore and petroleum drillholes created a geological map of basement lithologies and structures. Stratigraphic drilling has targeted areas with no data to constrain lithologies or their ages, with four key areas selected for drilling in far northwestern NSW. Information on the thickness of cover sequences over resistive basement interpreted from AEM inversion models has proven useful during the selection of drilling locations. Seven stratigraphic drillholes were completed within NSW using a combination of mud rotary and diamond drilling. All holes penetrated surface regolith, as well as sedimentary rocks of the Eromanga Basin, to achieve approximately 50 metres of basement core for analyses. Resulting improvements to geological understanding and development of exploration techniques will be a keystone to progress future investigations in the southern Thomson Orogen.