Sources of ore-forming fluid related to uranium mineralization in the Jahaz deposit, North Delhi Fold Belt, India: Inferences from carbon and oxygen isotopic studies

The Jahaz uranium deposit is one of the several uranium occurrences along the “albitite line” of the North Delhi Fold Belt, India. U-mineralization in the Jahaz area is metasomatic-type, medium-tonnage, low-grade, and occurs as veins and dissemination in the intensely altered rocks. Detailed petrographic studies of the mineralized zones indicate a close association of calcite and metallic minerals. Hence, carbon and oxygen isotopic analyses of calcites were carried out to decipher the sources of hydrothermal fluids related to U-mineralization. The calcites of the Jahaz area are categorized into three types (calcite-1, calcite-2, and calcite-3) based on their mode of occurrences in host rocks. Calcite-2 and calcite-3, occurring in cavities and fractured portions of the rocks are linked to uranium-sulfide mineralization. The results of carbon and oxygen isotope analyses of calcite-2 and calcite-3 indicate that the hydrothermal fluids were derived from a magmatic source. The δ 18 O values align with metamorphic fluids, while the slight positive correlation in the δ 13 C–δ 18 O implies fluid mixing during calcite precipitation at a lower temperature. The isotopic signatures of δ 18 O strongly suggest a mixing of fluids derived from granitic magmatism, metamorphism and meteoric nature. The close association of uranium and metasomatic mineral phases in intensely altered rocks indicates that fluid induced rock alterations played an important role to form enriched zones of uranium in Jahaz deposit.