Geological appraisal of radioactive mineral occurrence at Ahl in Mansehra granite, North West Pakistan

Abstract

An extensive radiometric survey in Mansehra Granitic Complex resulted in the discovery of secondary uranium mineralization in an over thrusted crushed part of Mansehra granite at Ahl. The crushed part indicates a roughly NS trending fault zone along the contact with Tanawal (Tanot) formation. Uranium mineralization consists of andersonite and uranophane. It reappears on the surface of granite after scratching within few days, as a result of precipitation from ground water. This prospect was investigated by shallow drilling of 18 holes totaling 1560 meters depth. 45 anomalous zones were encountered in drill holes ranging from 39-1100 ppm U₃O₈.

Exploration data revealed thick sedimentary pile consisting of alternating sandstone and clay below crushed part of granite pointing to an intra-mountain basin. It is concluded from the data collected so far that an intermountain basin with torrential stream deposit near Ahl has trapped the labile uranium leached from crushed granite by ground water. Such an intra-mountain basin has yielded deposit at the contact of basement and overlying sediments. It is likely that this basin may have a comparable potential.