Anomalous uranium concentration in tourmaline-bearing leucogranite of Higher Himalaya, Nuranang, Tawang district, Arunachal Pradesh, North East India

Here we report anomalous uranium concentration in tourmaline-bearing leucogranite occurring at Nuranang, Tawang district, Arunachal Pradesh, North East India. The leucogranite occurs as concordant layers parallel to gneissic foliation, similar to the gneisses of the Palaeopro­terozoic Se La Group. It is medium to coarse-grained, and is composed of quartz, potash feldspar and plagioclase as dominant minerals with variable proportions of muscovite, biotite, tourmaline and garnet. Apatite, zircon and pyrite are accessory minerals. Geochemically, the leucogranite is alkali-rich, peraluminous and highly differentiated. It is emplaced in a syn to late orogenic collision tectonic setting. Analyses of 10 granite samples collected at 500 m intervals show relatively high radioelemental concentration (U: 5–96 ppm, Th: 5–23 ppm, K: 2.23–7.72% and Th/U; 0.07–1.00, n = 10) compared to normal granite. Anomalous uranium concentration in the leucogranite is observed in a 200 m ´ 50 m area at Nuranang. Samples from this area have assayed 0.016–0.029% U3O8 and <0.005% ThO2. Leachable U3O8 content determined in five samples varies from 81.25% to 87.50%. Preliminary studies indicate that uranium is in the adsorbed state associated with iron oxide and alte­red feldspar/clay. The findings of anomalous uranium concentration in tourmaline-bearing leucogranite likely open up a new target area for uranium search in the Higher Himalaya of Arunachal Pradesh