Radiometrics

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Radiometrics is a measure of the natural radiation in the earth's surface, which can tell us about the distribution of certain soils and rocks. Geologists and geophysicists routinely use it as a geological mapping tool to tell them where certain rock types change. Radiometrics is also useful for the study of geomorphology and soils.

Radiometrics is also known as Gamma-Ray Spectrometry. A radiometric survey measures the spatial distribution of three radioactive elements (potassium-K, thorium-Th and uranium-U) in the top 30-45 cm of the earth's crust. These three elements are the 'biggest peaks' on a much broader spectrum of natural radioactivity. The abundances of K, Th and U are measured by detecting the gamma-rays produced during the natural radioactive decay of these elements. Further information on radiometrics.

North Central Radiometrics

Airborne geophysical surveys, including the measurement of radiometrics, were collected during the early 1990's as part of the National Geoscience Mapping Accord with the then Australian Geological Survey Organisation (formerly BMR, and now Geoscience Australia) (external link). The lower part of the image is part of the Ballarat 1:250 000 mapsheet with a flight line spacing of 400 metres and a sensor height of 80 metres. The northern part is from the St Arnaud 1:250 000 mapsheet, which was collected in association with CRA Exploration. Lighter/whiter areas on this image generally reflects a deeply weathered, though outcropping, region of sedimentary bedrock, which has a higher response of K, medium response of Th, and a lower response of U. Green areas indicate higher Th relative to K and U, particularly in the basaltic area along the Avoca and Loddon rivers. Very high K derived from the breakdown of K rich minerals in granites reflect that rock type in the areas shown as magenta west and south west of Lexton, west of Clunes and around Dunluce in the north. Along stream and river channels, the colours often reflect the source of the alluvial materials.