URANIFEROUS CALCRETE MAPPING USING HYPERSPECTRAL REMOTE SENSING

Calcrete, the calcium carbonate duricrust generally occurs in arid/semiarid region. Globally, it has been used as a non-traditional constructional material. The recent discovery of calcrete hosted secondary uranium deposits in Australia and Namibia has kindled interest in exploration of calcretes in many parts of the world. In this study, palaeochannel related calcretes of the Thar desert, India is explored as a possible source for uranium mineralization. The adopted exploration strategy includes mapping of calcretes using hyperspectral satellite data, in-situ radiometric survey, analyses of field collected samples for mineralogy and geochemistry. Calcretes along palaeochannels were mapped using Hyperion data, field spectra and Spectral Angle Mapper (SAM) technique. It was found that the adopted technique could also differentiate high-, and low-Mg calcretes with 72% accuracy. Mineralogy of calcrete includes calcite (40-60%), quartz (30-45%) and feldspar (10-15%) with minor amount of clay minerals (montmorillonite, kaolinite, illite, goethite). In in-situ radiometric survey, the range of uranium, thorium and potassium in the calcretes varies from 2.4-1 1 ppm, 5 -2 8.2ppm, and 0.8-4.2% respectively.