YANG Tongxu, YU Reng'an, RONG Hui, LI Tong, ZHU Qiang, SI Qinghong, TU Jiarun, PENG Shenglong
North China Geology. 2023, 46(4): 35-46.
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The northeastern edge of the Ordos Basin is one of the important sandstone type uranium resource bases in China, with multiple large and ultra large uranium deposits distributed. On the basis of fully summarizing previous research results, this paper systematically contrasts the uranium deposits in the northeastern margin of the basin and the Middle Jurassic Zhiluo Formation in non mining areas from petrology, geochemistry and other aspects, and discusses their differences and implications for uranium mineralization. The analysis results show that: (1) the main element content of the Zhiluo Formation sandstone in the study area is similar to that of the active continental margin sandstone, with SiO2 content gradually increasing from the Daying uranium mining area on the basin edge to the Wushenqi area within the basin, CaO gradually decreasing, and Na2O and K2O not changing much; (2) The distribution of trace elements is similar, with obvious enrichment of large ion lithophile elements such as Rb, Ba, Pb, and depletion of high field strength elements such as Nb, Ta, Ti. The content of Y, Yb, and Lu is low, and the content of Sr is medium, indicating that the source area of the Zhiluo Formation sandstone in each region is a typical subduction zone environment; The distribution pattern of rare earth elements is generally similar. From the edge of the basin to the inside, the content of U element decreases, the "right tilt" of the spider web gradually flattens, LREE gradually decreases, and the change in HREE is not significant; (3) The parent rock of Zhiluo Formation sandstone source area in the northeast of Ordos Basin is volcanic arc granite, which may be formed in the active continental margin environment related to subduction; (4)There is a positive correlation between La and Ce elements and U in the sandstone of the Zhiluo Formation in various regions of the northeastern Ordos Basin. During the sedimentation of the Zhiluo Formation, the ancient water environment was freshwater and oxygen rich. From the northeast to the central part of the basin, the ancient climate gradually became humid, which has good prospecting indicating significance.
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