GENESIS OF URANIUM MINERALIZATION IN JAHAZ, KHETRI BELT, ARAVALLI CRATON, INDIA

Abstract

Jahaz, a uranium deposit along the "albitite line" of Rajasthan, India, is hosted within the Meso-Proterozoic metamorphic rocks of the Delhi Supergroup. The mineralization is confined to brecciated and sheared metasediments and extends over a ~ 2 km strike length with an average thickness of 3.78 meters. The Jahaz deposit is medium tonnage (3570 tons) with a 0.01 cut-off grade of U3O8. The principal metallic minerals in the mineralized zones are uraninite, molybdenite, pyrrhotite, pyrite, chalcopyrite, and minor brannerite. Quartzite, amphibolite, garnetiferous quartz biotite schist, and graphite schist are the major rock types in this area. The garnetiferous quartz biotite schist and amphibolites are sheared/albitized, and U-mineralization is mostly confined to the albitized zones. The metamorphic mineral assemblage found in host rocks are annitemagnesiohornblende- ferrohornblende-bytownite-quartz-anorthite with almandine-staurolitecorundum- ilmenite. Four hydrothermal-metasomatic stages have been established: (i) early hydrothermal, (ii) Na±K, (iii) Na-Ca-Mg, and (iv) late hydrothermal. The study area experienced a ductile, ductile-brittle transition to a brittle shear deformation, where the early hydrothermal and Na±K metasomatic alteration stage is correlated to ductile deformation (700 °C-500 °C), Na- Ca-Mg metasomatic stage is with ductile-brittle transition to brittle deformation (500-280 °C) and late hydrothermal stage with brittle deformation (≤ 280 °C). The quartzo-feldspathic, milky quartz and gray quartz veins developed during early hydrothermal stages and are unrelated to mineralization. The fluid responsible for the first (Na±K) metasomatic stage was rich in Cl, and albite-1, amphibole-1, chlorite-1, calcite-1, biotite-1, quartz-1, and sericite formed due to the replacement of the parent metamorphic minerals. The occurrence of albite-2, amphibole-2, chlorite-2, calcite-2, titanite-2, quartz-2, and apatite along veinlets/cavities due to the precipitation of dissolved components from F-rich fluids related to second (Na-Ca-Mg) metasomatic stage. The quartz-3, calcite-3, and muscovite-1 veinlets represent the last hydrothermal activity and overprinted the earlier hydrothermal-metasomatic stages. The Na+, Cl- , H2O, CO2, Mg2+, S2-, F-, and PO4 3- bearing hydrothermal fluids were responsible for different stages of metasomatic-hydrothermal alteration and associated U-mineralization. The Na-Ca-Mg metasomatic stage is considered the main mineralization stage and is controlled by the ductilebrittle shear regime.