Abstract
The Kaladgi Basin of the Dharwar Craton, southeast India, hosts Proterozoic unconformity-related uranium (U) mineralization controlled by faulted contacts between Archean basement and Proterozoic cover sediments. To understand the ore-forming processes, 25 core samples from the Cave Temple Arenite were analyzed using whole-rock geochemistry and fluid inclusion microthermometry. U concentrations reach up to 0.13% U3O8 in the basal arenite and lower conglomerate, whereas the basement schist records only 0.0017% U. Whole-rock data reveal high SiO2 contents (72–97 wt.%), variable Al2O3 (0.4–12.9 wt.%), and enrichments in U (0.38–6.63 ppm), Th (1.5–13.7 ppm), and trace elements such as Cu, Pb, and Ni relative to average sandstones. ΣREE values vary from 36.9 to 404.6 ppm, with LREE-enriched patterns [(La/Sm)Cn = 2.3–19.7)] and flat HREE [(Gd/Yb)Cn = 0.65–3.1)]. Fluid inclusions are predominantly aqueous biphase, with homogenization temperatures of 78–227 °C and salinities of 0.2–23.2 wt.% NaCl equivalent. The coexistence of liquid- and vapor-rich inclusions with identical temperature ranges but contrasting salinities indicates fluid boiling, which destabilized U-bearing complexes and promoted precipitation of pitchblende and coffinite. These results suggest that U was leached from fertile granitoids and transported by oxidized brines along reactivated faults, with boiling and fluid–rock interaction at the unconformity surface, which becomes a U deposition environment. This study provides the first evidence of fluid boiling as a mechanism for U mineralization in the Kaladgi Basin. By integrating fluid inclusion microthermometry with whole-rock geochemistry, it establishes a fluid evolution, geochemical alteration, and fault reactivation for U deposition.