SEDIMENTARY FACIES AND URANIUM METALLOGENESIS OF YIMIN FORMATION IN THE EAST OF CHENQI FAULT DEPRESSION, INNER MONGOLIA

The Chenqi fault depression in eastern Inner Mongolia is an Early Cretaceous basin among the Hailar basin group. It is covered by the Tongbomiao, Nantun, Damoguaihe and Yimin formations. This mono-faulted basin is distributed nearly east to west, with strata inclining to southeast. During the depositional period of the Yimin Formation, the Chenqi fault depression entered the stage of reduction, when the fan delta in the south advanced to the center of the basin. The basin then was filled with a large number of marsh deposits to form coal-bearing strata. Simultaneously, with the northward regression of the lake, small river delta was formed on the northern slope of the basin. The water with uranium and oxygen from the pre-Quaternary gully and river channels vertically or laterally infiltrated into the oxidized lignite layer at the top of the watertight stratum. Uranium was then adsorbed by carbon deposits with secondary mineralization in the upper part of the coal seam. Therefore, this uranium mineralization belongs to phreatic water oxidation type.