The Radiometric Map of Australia

Geoscience Australia and the Australian State and Territory Geological Surveys have systematically surveyed most of the Australian continent over the past 40 years using airborne gamma- ray spectrometry to map potassium, uranium and thorium elemental concentrations at the Earth's surface. However, the individual surveys that comprise the national gamma- ray spectrometric radioelement database are not all registered to the same datum. This limits the usefulness of the database as it is not possible to easily combine surveys into regional compilations or make accurate comparisons between radiometric signatures in different survey areas. To solve these problems, Geoscience Australia has undertaken an AustraliaWide Airborne Geophysical Survey (AWAGS), funded under the Australian Government's Onshore Energy Security Program, to serve as a radioelement baseline for all current and future airborne gamma- ray spectrometric surveys in Australia. The AWAGS survey has been back-calibrated to the International Atomic Energy Agency's (IAEA) radioelement datum. Wehave used theAWAGSdata to level the national radioelement database by estimating survey correction factors that, once applied, minimise both the differences in radioelement estimates between surveys (where these surveys overlap) and the differences between the surveys and theAWAGStraverses. The database is thus effectively levelled to the IAEA datum. The levelled database has been used to produce the first 'Radiometric Map of Australia' - levelled and merged composite potassium (% K), uranium (ppm eU) and thorium (ppm eTh) grids over Australia at 100m resolution. Interpreters can use the map to reliably compare the radiometric signatures observed over different parts of Australia. This enables the assessment of key mineralogical and geochemical properties of bedrock and regolith materials from different geological provinces and regions with contrasting landscape histories.