Research on diagenesis of the sandstone-type uranium deposits in Dongsheng area, Ordos Basin

Synthetic methods of thin section petrography, scanning electron microscope, electron microprobe, energy spectrum analysis, cathodoluminescence, isotopic analysis and temperature measuring for fluid inclusions were used in analyzing sandstone samples collected from the Zhiluo Formation in order to fully understand the diagenesis evolution and the mineralizing response as well as the genesis of the uranium-bearing sandstone in Dongsheng area. The result shows that (1) the sandstone include lithic silicarenite, feldspathic litharenite and litharenite; (2) the authigenic minerals include clay minerals, carbonate minerals, siliceous and ferric minerals; (3) the physical property of sandstone is obviously controlled by diagenesis; and (4) the sandstone with favorable physical property is propitious to migration and storage of ore-forming fluid, and finally, forming the ore deposit. The sandstone of the Zhiluo Formation had undergone the early diagenetic stage (periods A and B) and the epidiagenetic stage. The evolution of diagenetic environment is in the order of acidic oxidation, alkalescent deoxidization, acidity to transitional environment of oxidation-deoxidization and acidity-alkalescence. The uranium exists in forms of pre-enrichment uranyl ion, active uranyl ion, dispersive adsorptive uranium and uranium mineral, respectively. In addition, the authors also hold that the formation of the sandstone-type uranium is not only related to the oxidation-deoxidization environment, but also closely related to the acidic-alkaline transitional environment, which are propitious to uranium mineralization in sandstone.