Geology and uranium mineralisation around Ampulli Area, Papum-Pare District, Arunachal Pradesh, North-East India

Uranium mineralisation associated with Middle Proterozoic Bomdila Group (Daling equivalent) metasediments have been located intermittently over a strike length of 310 m with 0.11 to 2.0 m thickness around Ampulli area of Papum-Pare district, Arunachal Pradesh. The metasediments trend NE-SW and dip 20°- 85° due either side. The grab and trench samples assayed 0.012 - 0.36% eU₃O₈, 0.006 - 0.19% U₃O₈ (beta/gamma), 0.009 - 0.235% U₃O₈ (Chem.) and less than 0.010% ThO₂. The host rocks have been identified as tourmaline bearing biotite-quartz schist, garnet bearing muscovite-biotite-quartz schist and muscovite-biotite schist. Uraninite, brannerite and U-Ti complex are observed with uranocircite and meta-uranocircite, the secondary uranium minerals. Replacement of uraninite by molybdenite and pyrite suggested earlier oxide and later sulphide phase. Partial chemical analysis indicated aluminous nature of the host rock and their high K₂O/Na₂O (3.3-10.73) ratios are suggestive of predominance of potash feldspar over sodic and effects of potash metasomatism. Both syngenetic as well as epigenetic hydrothermal origin of uranium mineralisation has been suggested. (author)