鄂尔多斯盆地东北部直罗组砂岩岩石学特征与铀矿化关系研究

摘要

该文通过薄片鉴定、扫描电镜等手段，结合分析化验数据，分别对鄂尔多斯盆地纳岭沟地段和大营地段直罗组下段砂岩碎屑及填隙物的成分、含量及微观结构特征进行对比研究，确定微观特征差异并初步探讨差异原因，建立其与铀矿化的关系。研究表明，纳岭沟地段与大营地段，在碎屑成分和填隙物方面均存在一定的差异。纳岭沟地段碎屑含量高，而胶结物及粘土含量较低，这一方面表明纳岭沟地段相比大营地段更靠近物源，长石风化程度相对较低；另一方面，由于目的层埋深不同而导致的成岩强度的差异也是造成岩石微观特征差异的重要原因。基于对含矿砂岩微观特征的研究，笔者认为纳岭沟和大营地段与东胜皂火壕地段经历了基本相同的铀成矿作用，大致可分为早期主成矿和后期再改造两个阶段。造成绿色调砂岩的主要原因是由于后期油气还原蚀变而形成的绿泥石。在成矿过程中，方解石与铀矿物的沉淀有着密切的联系。这为下一阶段东胜西北部地区铀矿勘查预测提供了理论依据。%In this paper, we examine the composition and content of interstitial material and the microscopic structure characteristics through the microscopic observations, scanning electron microscopy analyses combined with XRD data of the lower member of the Zhiluo Formation in Nalinggou and Daying areas. The microscopic characteristics were identified and preliminary discussion on the differences of sandstones from the two areas were made to establish the relationship between the microscopic characteristics of ore-hosting sandstone and uranium mineralization. Research results show that there is certain difference between the clastic composition and the interstitial material in Nalinggou and Daying areas. The sandstones in Nalinggou area have higher detrital content and lower cement and clay content as compared to that in Daying area. On one hand, Nalinggou area is located closer to the provenance as compared to Daying area, leading to the disintegration of feldspar. On the other hand, the differences of microscopic characteristics in ore-hosting sandstone resulted from the difference in the intensity of diagenesis that was caused by the depth of the lower member of the Zhiluo Formation. As mentioned above, we consider that Nalinggou and Daying areas experienced the same uranium ore-formation process as Zaohuohao area. The uranium mineralization can be divided into two stages, i.e., the early main mineralization and later reconstruction enrichment. And the green color of the sandstone came from the chlorites formed by the asending reduction fluids. In the process of mineralization, uranium minerals and calcite were precipitated simultaneously. The study results provide a theoretical basis for the uranium exploration in the northwest of Dongsheng area.