Based upon research on alteration in the Dongsheng and Huangling uranium mineralised areas, Ordos Basin, three stages have been distinguished in the lower member of the Zhiluo Formation: an early-stage red oxidation of hematization and goethitization; a middle-stage yellowish green and greyish blue hydrocarbon related reduction of smectitization, chloritization, pyritization; and a latestage yellow oxidation of goethitization and limonitization.
The fact that the mean TOC value of red sandstone and yellowish green and greyish blue sandstone are evidently lower than that of the original grey sandstone may indicates that the yellowish green and greyish blue sandstone have suffered oxidation before hydrocarbon reduction. In addition, residual red alteration sand bodies are observed as inclusions in the yellowish green and greyish blue sandstone in Dongsheng area, while in Huangling area the oil-immersed sands occur along fractures and unconformity interfaces in red alteration sands.
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