关键词: 鄂尔多斯盆地, 直罗组下段, 沉积特征, 砂岩型铀矿

Abstract: The lower member of the Middle Jurassic Zhiluo Formation in northern Ordos Basin is the main ore-hosting layer of sandstone-type uranium deposits. The genetic type, geometric shape, and physical properties of sandstone-bearing strata control the size and spatial distribution of sandstone-type uranium deposits. Previous studies on the genesis, geometric shape and physical properties of ore-bearing sand bodies that are controlled by sedimentation and diagenesis have effectively supported the exploration of sandstone-type uranium deposits in the Eastern North of the Ordos Basin. However, continental sedimentary environments are characterized by relatively rapid changes and significant regional variations. The sedimentary environment, the genesis and spatial distribution of the sand body of J2z1 in Bayinqinggeli-Sutaimiao area on the western side of the northern basin are still unclear. In order to expand the prospecting space, we studied the 5300 m long cores and logging data from 35 wells in the lower member of Zhiluo Formation, and carried out core inspection, microscopic identification, single well analysis, cross-well profile analysis and sand content isoline analysis of this stratigraphic unit in the western periphery of the northern basin. The results show that: (1) the sandstone types in the lower member of the Zhiluo Formation in the Bayinqinggeli-Sutaimiao area are mainly medium-coarse grain lithic feldspar sandstone and feldspar lithic sandstone; (2) delta plain subfacies were mainly developed in the study area, which can be further subdivided into branching channel, crevasse fan, interdistributary bay, swamp and mud microfacies; (3) based on the analysis of ore-bearing construction, uranium source characteristics, and tectonic characteristics, it is concluded that the eastern part of the study area has a great metallogenic potential to necessitate further exploration work in this area. The finding of this study provides an important geological basis for the exploration of sandstone-type uranium deposits in the Western peripheral areas.

Key words: Ordos Basin, lower member of Zhiluo Formation, sedimentary characteristics, sandstone-type uranium deposit