Granite core samples (n=14) from the Gogi-Kurlagere fault zone in the central part of the Bhima basin were studied in terms of LREE, Y and Zr mobility during uranium mineralization. LREE, Zr and Y along with LILE (Ba, Rb) and P show behavioral differences in the mineralised and the non-mineralised samples. Average ∑LREE in mineralised granite (240 ppm) is higher than in non-mineralised samples (157 ppm). The average Zr and Y in the mineralised granite are 193 ppm and 17 ppm, while the corresponding abundances of these elements in non-mineralised portion are 148 ppm and 11 ppm respectively. Besides enrichment of U, Th, Ba, Pb and Rb and depletion of Sr are observed in mineralized granite in comparison to non-mineralized granite. Hydrothermal alteration has led to the mobility of these elements, which again dependent on the overall geochemical behavior of the migrating fluid. REE and Y in association with uranyl [(UO 2)2+] ion were transported as carbonate complexes like [UO2 (CO3)3]4- and [REE (CO3)3]3- and were later incorporated into favourable structural loci by precipitating minerals like pitchblende and coffinite.

Uranium deposit at Gogi area is located along the E-W Gundahalli-Gogi-Kurlegere (GK) fault, in the brecciated impure limestone of Shahabad Formation of the Bhima Group of sediments and the basement granite in the central part of the Meso-Neoproterozoic Bhima basin. Uranium mineralisation is associated mainly with sulphide bearing minerals and secondary calcite. Ore microscopic studies indicate that among the sulphide minerals pyrite is predominant (about 98%) with subordinate amounts of chalcopyrite, chalcocite, marcasite, arsenopyrite and galena. Megascopically, three different varieties of pyrite viz., euhedral, lumpy and vein types are identified in the limestone and siltstone. Ore microscopic studies reveal that vein type pyrite and lumpy pyrite are fractured and crushed. Euhedral pyrite is idiomorphic and devoid of any fractures. The pyrite samples were analysed for δ34S sulphur isotopes. The δ34S values show a wide range from −30.51 to +20.77‰ (Canyon Diablo Troilite, CDT). δ34S values of pyrite can be classified into three groups depending on the values. High values of +17.73 to +20.77 ‰ (CDT) of euhedral pyrite (Py-I) indicate sedimentary pyrite formed due to bacterial reduction of sea water sulphate in relatively closed system, while pyrite (Py-II) having negative values of δ34S imply bacterial reduction of sea water sulphate in open system. The third group (Py-III) of pyrite have δ34S values of −0.51‰ (CDT) and 7.38‰(CDT), indicating their magmatic/ hydrothermal origin. Sulphides in the deformed sediments acted as reducing agent for uranium precipitation.