内蒙古二连盆地呼仁布其凹陷白垩系铀矿化特征与找矿远景

二连盆地是我国煤炭、油气、铀矿等资源的重要勘查基地,其中砂岩型铀矿的找矿方向和找矿突破一直是盆地铀资源勘查的重点。呼仁布其凹陷为二连盆地北部巴音宝力格隆起上的一个次级凹陷,为一相对独立的地质构造单元,在古生代基底之上沉积了厚层的中新生代地层,其中下白垩统赛汉组沉积了一套扇三角洲-湖泊相的含煤碎屑岩建造,地层埋深浅、厚度稳定,发育泥-砂-泥结构,砂体较发育,岩石具有黑色和灰色原生地球化学特征,具备铀矿成矿基本条件。本文以煤田钻孔资料"二次开发"作为铀矿勘查新思路,对凹陷中部地区收集的煤田钻孔测井成果开展了综合研究,在下白垩统赛汉组中圈定出规模较大且连续的放射性异常,显示出较好的找矿前景。通过对呼仁布其凹陷大地构造条件、铀源、地层-岩相、岩性、古气候与地貌、古水文地质特征等的系统分析,择优重点选择煤田铀异常孔进行钻孔验证,发现了具有工业意义的铀矿孔,在赛汉组中发现了两个稳定的铀矿化层,第一层铀矿化受到潜水氧化带的控制,位于潜水氧化带界面底部的泥岩中,为垂向氧化型成矿类型;第二层铀矿化受到层间氧化作用的控制,为典型的侧向氧化层间氧化型成矿类型。指出煤田钻孔伽马异常高值区可作为下一步铀矿勘查工作的方向。

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.