Calibration and modelling of airborne gamma-ray data with surface geochemistry, catchment boundaries and geological units - providing new insights into the distribution of K, Th and U across the Australian continent  

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Abstract

Two major geochemical datasets recently compiled are the National Geochemical Survey of Australia (NGSA) and the Radiometric Map of Australia. The geochemical survey of Australia measures floodplain sediments from 1186 catchments, covering ~80% of the country (average sample density 1 sample per 5500 km2). Samples were collected at two depths: 0-10 cm below the surface and between on average 60 and 80 cm depth. Samples were dried and sieved to either <2 mm (coarse) or <75 mm (fine) fractions, yielding four samples per site. The Radiometric Map has been generated by merging all available gamma-ray surveys into one seamless and levelled dataset with a consistent radioelement datum. The new map enables quantitative assessment of the distribution of potassium (%K), uranium (equivalent ppm U) and thorium (equivalent ppm Th) over about 80% of the Australian landmass. These datasets, together with geochemical assays of rock and regolith materials from the national OZCHEM databases, have been integrated and analysed at a national scales to better understand the distribution of K, Th and U. Surface concentration of these elements are associated with primary and secondary factors. Primary factors relate to the lithology and mineralogy of the parent material, whereas, secondary factors relate to low pressure and temperature hydrothermal alteration processes and weathering. To increase the utility of these data for mineral exploration we have calibrated the airborne radioelement grids using rock and sediment geochemistry to generate surface geochemical maps of K, Th and U in rocks and regolith materials. These datasets and thematic maps derived from modelling provide a broad framework in which to interpret more localised mineral systems. Systematic differences between the measured geochemistry and radioelement estimates derived from gamma-ray spectrometry provide new insights into the limitations of the gamma-ray spectrometric method for radioelement mapping.

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nonGeographicDataset

eCat Id

71477

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Keywords

• External Publication

( Theme )

• geochemistry

( Theme )

• gamma spectroscopy

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2011-01-01T00:00:00

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Creative Commons Attribution 4.0 International Licence    

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