An appraisal of uranium deposits of India and their style of deposition with reference to the Paleoproterozoic great oxidation event

Abstract

ABSTRACT Evolving atmospheric oxygen levels during the early Earth history had a profound impact on Earth’s surface processes, especially on the mineralization of redox-sensitive elements such as iron (Fe) and Uranium (U). Here we present a review of the effect of the Great Oxidation Event (GOE) that started at ~2.44 Ga on the style of Uranium mineralization with reference to Indian uranium occurrences. GOE was responsible for the initiation of intense chemical oxidative weathering of the Neoarchean U-rich K-granites mobilizing U from the source rocks in the U6+ soluble state. By 2.32 Ga, anoxic/euxinic conditions in the oceans developed on a global scale mainly due to the bacterial sulphate reduction that was triggered by enhanced sulphate concentrations in the ocean caused by the GOE. Such a development of anoxic/euxinic conditions acted as a sink for the hexavalent U by reducing it to tetravalent state and its deposition on a large scale in the strata of post-2.0 Ga age. Majority of Uranium deposits of India are hosted in the Proterozoic rock formations unlike the global pattern, where the Phanerozoic strata are more prominent. Among the uranium reserves that occur in the Precambrian sequences of India, the mineralization during the 1.9 to 1.6 Ga time window constitute ~75% of the total. In India, the Archaean U occurrence is exemplified by the Bababudan quartz pebble conglomerates (~2.72 Ga) hosting detrital uraninite, while the Proterozoic period witnessed a marked change with most of the U deposits being of redox-controlled-type in sedimentary formations. A model is proposed to explain such an enrichment in Uranium reserves among the Proterozoic strata of India. It appears that the emplacement of large ion lithophile element (LILE)-enriched granites, the onset of GOE and ensuing oceanic anoxic conditions played a major role in controlling the Uranium mineralization of the late Paleoproterozoic in the Indian scenario.