Uranium Mineralisation in the Mahadek formation of Balphakram Area, South Garo Hills District, Meghalaya

Significant Sandstone-Type uranium mineralisation is recorded from the Rongcheng Plateau and Rongdi nala, located north and WNW of Balphakram Plateau, South Garo Hills district, Meghalaya. Mineralisation is associated with grey coloured, medium to coarse grained, poorly sorted arkosic Wacke-Subarkose suite of sandstones, belonging to the late Cretaceous Mahadek Formation. Sixteen uranium occurrences located 2-30 m above crystalline basement and with dimensions varying from 5 to 300 m × 0.5 to 4 m, have been identified. Grab samples have assayed up to 0.52% eU₃O₈ 0.46%U₃O₈ (beta/gamma) and <0.010%Tho₃. The fertile Precambrian basement crystallines constitute the source of uranium. Presence of organic matter and pyrite in the sandstone provided reducing environment for deposition of pitchblende as the principal discrete uranium mineral.