Abstract: 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.

Key words: microscopic features, Zhiluo Formation, Nalinggou, Daying, Ordos basin