Characteristics and genesis of sandstone uranium ore in Shuixigou group in the southwestern Tuhu basin

Based on the previous researches of Tuha basin, such as sequence stratigraphic framework and sedimentary environment analysis, the studies on the composition and content of mudstone minerals in Shuixigou group by the means of X-ray diffraction. Some minerals are found distributing unhomogeneous. Kaolite mostly exists in Badaowan formation and Sangonghe formation of Early Jurassic and its content can be up to 36.25%. Feldspar only distributes in Xishanyao formation of Middle Jurassic with a little content of about 4.86%. Chlorite distributes little (2.5% ±) in Badaowan formation and Sangonghe formation, while more in Xishanyao formation of about 26.57%. Montmorillonite also is little (3.75% ±) in Badaowan formation and Sangonghe formation, and relatively more in Xishanyao formation (7.84% ±). Combined with scanning electron microscope, from Badaowan formation to Xishanyao formation, diagenetic environments changed from sub-acid to sub-alkali, while Sangonghe formation has sub-acid depositional environments. These show that mudstone minerals as a assistant indication in strata comparison has some feasibility not only to compare strata but also to explain diagenetic and/or depositional environments. And the sub-alkali environment of the two major ore-bearing layers in Xishanyao formation proves that uranium deposits are under the reducing condition. (authors)