Uranium mineralization characteristics of Cretaceous period and prospecting direction of the Hurenbuqi depression in Erlian basin, Inner Mongolia

Erlian basin has rich coal, oil, natural gas and uranium resources, but the targeting and breakthrough of the prospecting for sandstone-type and sedimentary uranium deposits remain a focus in uranium resources exploration of this basin. Hurenbuqi depression is a subordinate depression on the Bayinbaolige uplift in the northern part of Erlian basin, which is a relatively independent geological tectonic unit. It deposited thick Mesozoic-Cenozoic strata above the Paleozoic basement. The Lower Cretaceous Saihan Formation deposited a set of fan delta-lacustrine coal-bearing clastic rocks. The burial depth of the strata is fairly shallow, the thickness is stable, the mud-sand-mud structure is developed, the sand body is especially well developed, and the rock has black and gray primary geochemical characteristics. Using the new idea of employing the data of coalfield drilling for second-round development of uranium resources, the authors conducted comprehensive research on the coalfield logging data collected from a certain area on the northwest margin of the basin and, as a result, delineated large-scale and continuous radioactive anomalies in the Lower Cretaceous Saihan Formation, showing a good prospecting prospect. Through a systematic study of tectonic conditions, stratigraphic facies, lithology, palaeoclimate, geomorphology, and palaeohydrology, the authors chose uranium anomaly holes in the coalfield to make drilling verification and found a uranium ore hole with the industrial significance. Two stable uranium mineralization layers were found in the Saihan Formation. The first layer is controlled by the phreatic oxidation zone, is located in the mudstone at the bottom of the interface of the phreatic oxidation zone, and belongs to the vertical oxidation type mineralization type. The second layer of uranium mineralization is a mudstone formation, and belongs to the typical interlayer oxidation type. The authors finally point out the direction of the next exploration work.