Behavior of Uranium mineralization in Siwaliks of Nangar Nai area; Dera Ghazi Khan

Abstract

The uraniferrous fluvial sedimentary rocks exposed in Nangar Nai area, D G. Khan District run along the eastern margin of Sulaiman Range and make a part of middle Siwaliks. The rocks are of vital importance for uranium exploration. These uranium accumulations are paleo-channel related and occur at places where the paleochannel is ducking in. The ducking out paleo channels are devoid of subsurface uranium mineralization despite of very good surface signature of radioactivity. The genetic model proposed for the source of these uranium deposits may be attributed to the primary rocks of the Himalayas coupled with volcanic and ash falls derived from the volcanic activities occurred in the northern & western parts of Pakistan. The uranium was liberated from the primary rocks, transported in solution along the fluvial sediments and deposited at suitable locations. Later enrichment accumulations have resulted in the formation of uranium ore accumulations.

Nangar Nai uranium mineralization is primarily a paleo-channel related ore body that was formed well below the present day water table in the form of a complex paleochannel cum ground water oxidized leach type sandstone deposit. The uranium was maninly transported and deposited by the paleo-channel and enriched by the accumulation phenomenon, Further enrichment was provided by the indigenous volcanic source. Due to later tectonic uplift of strata a part of the uranium-bearing horizon has been exposed to the surface, which was oxidized and eroded Major part of the ducking in paleo-channels has developed a redox interface below the water table and resulted in an ore body. Remobilization has caused leaching of uranium from western extremities of the ore body that has been transported to the eastern peripheries in the form of further enrichment on existing ore accumulations. This has resulted in positive disequilibrium of uranium ore.