| Summary: | To further explore the diagenetic environment, uranium precipitation mechanism and mineralization mechanism of the sandstone type uranium deposit in Sifangtai Formation on the southern margin of Daqing placanticline in Songliao Basin, the systematic research has been by drilling core observation, rock slice, sandstone uranium containing carbonate cement carbon and oxygen isotopic analysis of the sandstone rock types in the study area, the types of carbonate cements, diagenetic stage and systemic research on the carbon and oxygen isotopic been characteristics, The results show that the uraniferous sandstone rock types are feldspar lithic sandstone and lithic feldspar sandstone, carbonate cement being divided into three periods.For the first time and second time, the priority is given to cement, including calcite, ferroan calcite, see very small amounts of iron dolomite.The value of δ13CPDB is -22.45‰--13.65‰, with an average value of -18.00‰.The value of δ18OPDB is -17.56‰--9.46‰, with an average value of -13.52‰, revealing that there are some organic matters involved.The paleosalinity Z value is between 75.98 and 90.97, which is fresh water deposit.The paleotemperature is between 67.31℃ and 94.92℃, and the diagenetic environment is judged to be in the stage A of early-middle diagenesis based on the above rock features, cementite types and diagenesis.The comprehensive analysis shows that the compaction and cementation of the sadnstone during the early diagenesis stage reduce the porosity of the uranium-bearing sandstone and inhibits the migration of oxygen-rich uranium-bearing fluid.As diagenesis and bruial depth increase, higher organic matter maturity in the hot decarboxylate effect, and the compaction of adsorbed water to form acid solution were formed by dissolution of the feldspar, carbonate cement secondary pore, in order to increase sandstone porosity and promote oxygen rich fluid infiltration of uranium migration.Underlying oil and gas with upward dissipation through fracture provide stratum with reducing agent, making uranium be precipitated and enriched large scale at the bottom of Sifangtai Formation.
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