Airborne magnetic, radiometric and satellite imagery for regolith mapping in the Yilgarn Craton of Western Australia

Abstract

The integrated use of airborne magnetic and radiometric data, and SPOT Panchromatic and LANDSAT Thematic Mapper satellite data has proved effective for regolith mapping in the Yilgarn Craton of Western Australia. They can form the basis for designing appropriate soil sampling and regional exploration drilling in gold exploration programs. Horizontal derivative filters have been applied to airborne magnetic line data to enhance short wavelength magnetic responses of maghemite-rich lateritic weathering products within the regolith profile. Magnetised maghemite-rich pisolites often occur in buried Tertiary palaeo-drainage channels or within residual laterite horizons, and their distribution can be delineated with these filters. A new filter for magnetic data (REGMAG) is described that maps the distribution of short-wavelength responses and has proved effective in mapping magnetic structures in the regolith. Ratios of airborne radiometric potassium and thorium channels, and ternary images of potassium, thorium and uranium, are useful in highlighting the radiometric signatures of various weathering products in the regolith. A new ratio normalisation algorithm improves the resolution of ratioed data. Combined SPOT Panchromatic and LANDSAT Thematic Mapper satellite data are useful for landform mapping. Ratios of LANDSAT Thematic Mapper bands provide discrimination of various weathering products such as saprolite, pisolitic/nodular goethite and hematite-rich laterite, quartz and kaolinite rich alluvial cover, and red-earth calcareous clays. Examples from the Archaean Yilgarn Craton of Western Australia show how these processing techniques can reveal valuable information from remotely sensed data which can assist with regolith mapping.