阿其图乌拉地区下白垩统赛汉组结构及其砂体特征研究

Structure and sand body characteristics of Lower Cretaceous Saihan Formation in Aqituwula area

研究区位于腾格尔坳陷的北西部,区内铀矿化主要赋存于下白垩统赛汉组上段发育的古河道砂体中,因此,厘清找矿目的层赛汉组结构,尤其是砂体发育特征,有助于快速推进找矿工作进程,提升铀矿勘查效果。本文以研究区完成的可控源音频大地电磁(CSAMT)资料为基础,结合岩石电阻率特征及钻孔资料,对下白垩统赛汉组结构及其砂体发育特征进行了探究。研究结果表明:下白垩统赛汉组顶板埋深约150 m,由凸(隆)起向凹陷中心倾伏,都日木凹陷最大厚度约550 m,总体上为“泥—砂—泥”三层结构;其中上层泥岩厚度为80~100 m,中层主要发育辫状河及三角洲相砂体(主要分布于都日木凹陷),横向连续稳定,宽约8~13 km,厚度由北西向南东增厚至220 m,底层泥岩厚度为100~280 m。找矿目的层上述发育特征,为区内铀矿资源评价提供了地质—地球物理信息。

The study area is located in the north-west part of Tengger Depression,where uranium mineralization occurs mainly in the paleochannel sand bodies developed in the upper section of Saihan Formation of Lower Cretaceous.Thus,it is helpful to advance the prospecting and enhance the prospecting effect of uranium deposit that the structure of interest bed(Saihan Formation)for prospecting made be cleared,especially development characteristics of sand body.Based on the controlled source audio magnetotelluric(CSAMT)data completed in the study area,combined with rock resistivity and borehole data,the structure of Saihan Formation of Lower Cretaceous and the development characteristics of sand bodies are studied in this paper.The result shows that the roof of Saihan Formation of Lower Cretaceous is about 150 m deep and at inclination from the rise to the central sag.The maximum thickness of Durimu sag is about 550 m,which is composed of mud and sand and mud.The thickness of upper mudstone is 80~100 m.Braided river and deltaic sand bodies(mainly in Durimu sag)are developed in the middle layer,which are continuously stable in transverse direction,about 8-13 km wide,thickness increase to 220 m from NW to SE.The thickness of mudstone in the bottom layer is 100-280 m.The above-mentioned development characteristics of target strata provides the geological and geophysical information for uranium resources evaluation in the area.