The Radiometric Map of Australia

Abstract

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. We have used the AWAGS data 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 the AWAGS traverses. 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 100 m 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.

A map of radon flux at the Australian land surface

“…For Cowra and Mary River these were point measurements made using a hand-held gamma spectrometer, for the Tasmmanian survey these were determined from soil samples analysed with a germanium gamma detector and then adjusted to match aerial survey data on average. Other data are taken from airborne measurements (Minty et al, 2009 Schery et al (1989).…”

A weathering intensity index for the Australian continent using airborne gamma-ray spectrometry and digital terrain analysis

“…Australia is fortunate to have an extensive and well calibrated gamma-ray coverage at moderate to high resolution (Minty et al, 2009), without which this type of continental-scale analysis would not have been possible. Data acquisition in Australia was driven initially for mineral exploration, particularly U and more generally for geological mapping.…”

“…To honour the data recorded along the flightline, most surveys are only gridded to one fifth the flightline spacing. Flight line spacing for the national radiometric grid mainly included 400 m surveys but surveys with 1.5 km flight spacing were also used in places (Minty et al, 2009). Therefore the resolution of the airborne data is variable despite all the surveys being gridded to 100 m and consequently the accuracy of the weathering prediction will vary accordingly.…”

“…4a), which integrates over 540 surveys at a 100 m resolution (Minty et al, 2009). Potassium is expressed in percent and Th and U in parts per million.…”

Modelling the abundance of soil calcium carbonate across Australia using geochemical survey data and environmental predictors

“…The distribution of these elements varies in response to bedrock type, secondary weathering processes and soil formation (Wilford, 2012). Individual and ratio grids for K, eTh and eU were compiled from the radiometric map of Australia (Minty et al, 2009). Gaps in the radiometric map were filled by inclusion of gridded data from the Australia-Wide Airborne Geophysical Survey (AWAGS; http://www.ga.gov.au/ausgeonews/ausgeonews200812/ radiometrics.jsp).…”