Role of Provenance Composition in Uranium Mineralization in the Srisailam Sub-Basin, India: An Insight from Ree Modeling

Unconformity-related uranium deposits occur in close proximity to the unconformity between the Mesoprotero oic Srisailam Formation and the underlying Neoarchaean to Palaeoprotero oic granitoids along the northern part of Srisailam Sub-basin, Cuddapah Basin, India. The uranium in these deposits is presumed to have been sourced from the basement granitic rocks and/or the overlying sedimentary cover rocks. In the latter case, the provenance composition has played a critical role in controlling the intrinsic uranium content in the cover sedimentary rocks. However, to date, no systematic study has been undertaken to evaluate the influence of provenance composition on uranium budget of these cover sediments. In this study REE geochemical modelling has been employed to character! e the provenance in the Srisailam Formation and to assess its implications for uranium mineral! ation in the Srisailam Sub-basin. Considering the established stratigraphic relationships, spatial disposition of geological units, and available geochronological constraints, three potential provenance terranes, vi . the Eastern Dharwar Craton, the Nallamalai Fold Belt and the Krishna Province in the Eastern Ghats Mobile Belt (EGMB), were evaluated as possible source regions for the sediments of the Srisailam Formation. Rare Earth Element (REE) mixing calculations indicate that the Srisailam sediments, particularly those exposed along the northern margin of Srisailam Sub-basin, were predominantly derived from Eastern Dharwar Craton. The inferred source terrane comprises dominantly of tonalite granodiorite adamellite (TGA; 58%), with subordinate contributions from basalt (25%) and rhyolite (5%) from the greenstone belt, and a minor proportion of granite (12%). The felsic provenance rocks, namely tonalite granodiorite adamellite (TGA; U/Th = 0.33), granite (0.80) and rhyolite (0.40), are character! ed by higher U/Th ratios than the Upper Continental Crust (UCC; 0.26). The grey to dark-grey shales of Srisailam Formation exhibit a U/Th ratio of 0.35, comparable to the weighted U/Th ratio (0.38) average of the inferred provenance lithologies. In contrast, the sandstones of the Srisailam Formation display significantly lower U/Th ratio (0.17), interpreted to reflect uranium leaching by circulating, oxidi ing, basinal fluids during minerali ation. These relationships indicate that, in addition to the basement granitoids, the cover sediments of Srisailam Formation had acted as an important source of uranium during the formation of unconformity-related uranium deposits (e.g., Chitrial, Lambapur and Peddagattu) along the northern margin of the Srisailam Sub-basin.