Mapping of a granite batholith using geological and remotely sensed data: the Mount Edgar Batholith, Pilbara Craton

Abstract

The gamma-ray spectrometric data over an exposed granite batholith contains detailed information on its structure and composition. The information is poorly displayed in the conventional red-green-blue or hui-saturation-intensity colour-space images. Variation diagrams can be prepared showing the relationship between K, Th and U, and the data can be displayed as a map of distance along the average variation path, and deviation of the observed concentrations from this average variation path. Alternatively, the rocks can be separated into subdivisions of granite types, and these types mapped using separate classification layers. For the Mount Edgar Batholith, gamma-ray spectrometry results are compared with the results from other techniques ? rock sample geochemistry, petrography, air photo interpretation, field observations, structural studies, magnetic anomalies, and Landsat-5 Thematic Mapper data enhanced for geology. In this outcropping batholith the spectrometric data are thought to be superior technique in determining batholith structure and compositional variation, because of it has greater resolution than field mapping and rock sample geochemistry, and because of its tie to rock geochemistry that is lacking in magnetic anomalies.