Gamma ray spectrometry proves it worth as a mapping tool in granite-rich terrain

Geological map meridional portion ribeira belt

In areas with limited accessibility and/or a scarcity of outcrop, airborne geophysical techniques can sometimes be used to map geology. Gamma-ray spectrometry, for instance, works well in granitic areas because granites tend to have relatively high levels of gamma radiation from the decay of potassium, uranium and thorium.

Researchers at the University of Paraná in Brazil recently tested the application of gamma-ray spectrometry for geological mapping in an area of southern Brazil that contains a variety of granitic rocks. At the same time, they evaluated how topography changes and landslides affect the mobility of radionuclides in rugged or mountainous regions.

The researchers used a geophysical survey over the area flown by CPRM, the Geological Survey of Brazil, using a line spacing of 500 metres and a mean clearance of 100 metres. They transformed the data to apparent concentrations of potassium (K, %), equivalent in thorium (eTh, ppm), and equivalent in uranium (eU, ppm). Readings were taken every second, representing sampling intervals of about 75 metres. Geosoft Oasis montaj was used to process and analyze the resulting gamma-ray spectrometry data.

Read the full story on Earth Explorer, to learn more about the data and techniques used in the study.

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