The Radiometric Map of Australia*Brian Minty 1 2 Ross Franklin 1 Peter Milligan 1 Murray Richardson 1 John Wilford 1
1 Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia.
2 Corresponding author. Email: Brian.Minty@ga.gov.au
Exploration Geophysics 40(4) 325-333 https://doi.org/10.1071/EG09025
Submitted: 21 April 2009 Accepted: 13 September 2009 Published: 7 December 2009
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 Australia-Wide 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.
Key words: gamma-ray baseline, gamma-ray spectrometry, grid merging, radioelement datum.
Peter Percival (Geoscience Australia) assisted with the preparation of survey data before grid merging. His assistance is gratefully acknowledged. The AWAGS survey was flown by UTS Geophysics Pty Ltd, and funded under the Australian Government’s Onshore Energy Security Program. This paper is published with the permission of the CEO, Geoscience Australia.
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* *Presented at the 20th ASEG Geophysical Conference and Exhibition, February 2009.