| Ordos basin is one of the mainly oil-productive, gas-productive and coal-productive basin in China. Dongsheng sandstone type uranium deposit, the latest large deposit, is located in the northeast of the basin. The Dongsheng sandstone type uranium deposit has unique metallogenic features. Based upon detailed studies on metallogenitic geology setting, geological characteristics of ore deposit, epigenetic wall-rock alteration and ore-forming fluid of the deposit, the dissertation discusses the evolution of the low temperature fluid during the mineralization processes and geochemistry characteristics of fluid metallogeny emphasizedly and points out the metallogenic model of the sandstone type uranium deposit.Research on the characteristics of Ordos basin and metallogenic setting of Dongsheng sandstone type uranium deposit indicated that rigid block of the basin occurred faulting, tilting, uplifting and depressing and whole rigid block of basin were disturbed during the Indosinian-Yanshanian movement and Himalayan movement. During the mid-Jurassic and early-Cretaceous orogenic movement especially, uplift of basin, sedimentation interruption, infiltration of the surface-water and groundwater and lateral migration of oil can supply the material source and fluid dynamic for Dongsheng sandstone type uranium deposit. The neotectonic movement the uplifting and denuding of the basin were beneficial for the U element remobilization and multiple interlayer oxidation. Furthermore, around the Dongsheng district there have NE strike Langshan rock mass on the northwest, EW strike Yinshan rock mass on the north, all the granitic rocks and volcanic rocks could supply the uranium source for the deposit.The studies show that the ore-bearing stratum of Zhiluo group has two segments, the top layer is middle-fine motley sandstone and claystone, and the under layer could also be divided into two sub-layers, which top sub-layer is mostly gray-green sandstone and claystone, and under sub-layer is gray sandstone with bearing uranium. According to the mineralogy analysis,the sandstone of ore-bearing stratum is confirmed on lithic arkose. And the chemical composition analysis indicated that there are the same chemical composition between Zhiluo group sandstone and granitic rocks of Yinshan & Langshan area. Shapes of ore bodies show the blurry roll type, more plank type, layer type and lentoid type. The most part of uranium element are absorbed, and the coffinite is the primary uranium mineral, there are also some brannerite and a little uraninite.The contents variety of organic matter, S, Mn and Fe element in the different part of the Zhiluo group under layer show that the gray-green sandstone rock has occurred the interlayer oxidation. And the varieties of U, Se, V, Mo and Re elements on drill and section plane show the interlayer oxidation mineralization of the Dongsheng sandstone type uranium deposit. According to the analysis results, it is obviously the Zhiluo group is rich uranium sandstone rocks with the U contents of 4. 05~4.62×10-6.This paper studied the epigenetic alteration zones of the deposit. The plane alteration zones indicate the interlayer oxidation in the sandstone strata. There is three-layer alteration mode of the deposit in lengthways: the top alterations are limonitize, clay and carbonation which are in the upper layer of Jurassic system Zhiluo group, and middle alterations are chloritization of biotite and plagioclase, epidotization of plagioclase, clay alterations and carbonation in top sub-layer, under-layer alterations are epidotization of plagioclase and carbonation in under sub-layer of Zhiluo group which is the host rock of uranium deposit. In this deposit, there are three type alterations created by three mineralizing fluids. the first type is the acid oxygenic alteration with kaolinization, hematitization, limonitzation and the oxidation of organic matters; the second type is the weak acid & alkalescent reductive oil-gas alteration with epidotization, carbonation, chloritization, sericitization,...
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