松辽盆地大庆长垣南缘四方台组砂岩型铀矿碳氧同位素特征及铀成矿意义

为进一步探讨松辽盆地大庆长垣南缘四方台组砂岩型铀矿的成岩环境、铀沉淀机制及成矿机理，通过钻井岩心观察，岩石薄片，含铀砂岩碳酸盐胶结物碳、氧同位素分析，对研究区砂岩岩石类型、碳酸盐胶结物类型、成岩阶段以及碳、氧同位素特征进行了系统研究。结果表明:含铀砂岩岩石类型为长石岩屑砂岩、岩屑长石砂岩，碳酸盐胶结物可分为3个期次，以第一和第二期次为主，胶结物包括方解石、铁方解石，见极少量含铁白云石。δ13C_PDB值为-22.45‰~-13.65‰，平均值为-18.33‰，δ18O_PDB值为-17.56‰~-9.46‰，平均值为-13.52‰，揭示有一定有机质参与；古盐度Z值介于75.98~90.97之间，为淡水沉积；古温度介于67.31~94.92℃之间，结合以上岩石特征、胶结物类型及成岩作用判定成岩环境处于早成岩—中成岩阶段A期。综合分析认为:早成岩阶段砂岩的压实、胶结作用使含铀砂岩孔隙度减小，抑制含氧富铀流体运移；随着成岩作用进行，埋藏深度增加，有机质成熟度升高发生热脱羧基作用，与压实作用产生的吸附水形成酸性溶液对长石、碳酸盐胶结物等进行溶蚀形成次生孔隙，增大砂岩孔隙度，促进含氧富铀流体下渗运移，下伏油气由断裂向上逸散，为地层提供还原剂，使铀在四方台组底部大规模沉淀和富集。 

Carbon and oxygen isotopic characteristics and uranium mineralization significance of the sandstone-type uranium deposit in the Sifangtai Formation at the southern margin of Daqing placanticline in Songliao Basin

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 δ13C_PDB is -22.45‰--13.65‰, with an average value of -18.00‰.The value of δ18O_PDB 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.