鄂尔多斯盆地北部巴音青格利-苏台庙地区中侏罗统直罗组下段沉积特征及其铀成矿意义

鄂尔多斯盆地北部中侏罗统直罗组下段是砂岩型铀矿的主要赋矿层位，含矿层砂体的成因类型、几何形态和物性特征约束着砂岩型铀矿矿体的规模和空间分布。前人对盆地北东部赋矿砂体的成因、三维几何形态、沉积成岩作用控制下的砂体物性特征等作了深入细致的研究，有效支撑了北东部砂岩型铀矿的高效勘探。可是陆相沉积具有相变快、地区沉积差异显著的特征，盆地北部西侧的巴音青格利-苏台庙地区J2z1的沉积环境、砂体成因和空间展布尚不明确。为了扩大找矿空间，文章基于35 口钻井5300 m 直罗组下段的岩心、测井资料，在盆地北部西侧外围地区开展了钻孔岩心观察、镜下鉴定、单井分析、连井剖面分析以及含砂率等值线分析工作。研究认为：（1） 巴音青格利-苏台庙地区直罗组下段的砂岩类型主要为中-粗粒岩屑长石砂岩和长石岩屑砂岩；（2） 研究区内主要发育三角洲平原亚相，可进一步细分为分支河道、决口扇、分流间湾以及沼泽和泥沼微相；（3） 从含矿建造、铀源特征以及构造特征分析认为研究区东部成矿潜力较大，有必要 进一步开展勘查工作。上述认识为西部外围地区的砂岩型铀矿勘探提供了地质支撑。

Sedimentary Characteristics of the Lower Member of the Zhiluo Formation in Middle Jurassic and Its Uranium Metallogenic Significance in Bayinqinggeli-Sutaimiao Area,Ordos Basin

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 importantgeological basis for the exploration of sandstone-type uranium deposits in the Western peripheral areas.