Felsic Volcanic Rocks, a Potential Source of Uranium - An Indian Overview

Abstract

Felsic volcanics constitute a primary source of uranium for forming an economic deposit. All over the world, volcanic rocks have not received due attention they deserve in uranium exploration. The volcanogenic deposits have been grouped with “other deposits”, as they constitute a meager < 0.5% of world uranium resources. Exploration inputs in the western world have identified a number of uranium deposits associated with volcanic rocks. The uranium resources contributed by volcanic type deposits all over the world stand at 3, 62,000 te U3O8 (IAEA 2008 Compilation). The significance of acid volcanic rocks as a potential uranium source lies in the readily leachable form of their uranium content. A detailed study carried out in Australia to understand the spatial and temporal relationsh ip between the uranium deposits and the unmineralized, uranium enriched rocks from across the continent clearly indicated the role of the acidic volcanics as a potential provenance. Among the acid volcanics, rhyolites form an ideal source followed by welde d tuffs, ignimbrites, etc. The alkali or topaz rhyolite is ideal for its enrichment in many lithophile elements including uranium, which are amenable to subsequent leaching by meteoric water. In India the uranium exploration activities in the early 50 s till the 90 s were mainly confined to the Singhbhum Shear Zones, the Himalayas,Meghalaya plateau, parts of Central India and the geological environs of the Dharwar Craton. The granitic rocks, especially the peraluminous biotite – granite was always considered as a potential source for uranium and the geological environs closer to these granites always remained the first order targets. A number of small to medium size uranium deposits have been identified in Singhbhum Shear Zone, parts of Cuddappah, Bhima Basins and in Meghalaya. Now since the significance of the volcanic rocks, especially the felsic volcanics as a potential source of uranium has been clearly understood, it is imperative to reorient our exploration strategy to tap the potential of these volcanic rocks. The Malani Magmatic Province (MMP) in the northwestern part is the largest suite of an -orogenic acid volcanics in India occupying an area of 50000 sqkm. The Proterozoic Basins of India are replete with volcanic activity, mainly acid volcanism. In the southern and Central India, Dharwar and parts of Central Indian Craton also witnessed significant acidic igneous activities. The Cuddapah and the Vindhyan Basins have also recorded extensive acidic volcanic activity in the Papaghni, Chitrvati, Nallamalai Groups and Semri and Kaimur Groups respectively. In view of this the Proterozoic Basins mentioned above and the geological environs adjacent to the MMP deserve a re -look to have a proper assessment of their uranium potential, using integrated exploration inputs.