Petromineralogical aspects of uranium mineralisation at Deshnur, in Kaladgi - Badami basin Belgaum district, Karnataka

This paper discusses the petromineralogical aspects of uranium mineralization at Deshnur in the Kaladgi-Badami Basin, Belgaum district, Karnataka. The mineralization occurs as veins and veinlets along fractures in Badami arenites of Kerur formation. Alteration features like kaolinisation of feldspars is pronounced in the area. The sediments display deformational features like pulverization, fracturing, elongation and undulose extinction. Boehm twin lamellae are observed in quartz grains. The basement rocks of Deshnur display intense shearing and brecciation. Seven radioactive phases have been identified from petromineralogical studies. They are pitted uraninite, pitchblende, secondary uranium minerals along fracture planes and intergranular spaces, labile uranium present along grain boundaries, adsorbed uranium in kaolinite and substitution in refractory minerals like zircon. The presence of pyrite and pitchblende along fractures and intergranular spaces indicates that the mineralization at Deshnur is hydrothermal epigenetic type. From the mineral assemblage and textural associations, it is inferred that the temperature of mineralization is epi-to mesothermal in the range of 1000 to 3000 deg C and is fracture controlled. From the textural relationships an attempt has been made to understand the paragenetic sequence of the minerals. (author)