Ore-forming Fluid Characteristics of Hailijin Uranium Deposit in Songliao Basin:Petrogeochemistry Evidence From Ore-bearing Sandstones
The genesis of sandstone-type uranium deposits in the southwestern Songliao Basin is one of the key factors that restrict the breakthrough of uranium exploration.This article takes the Hailijin uranium deposit as the research object and carries out a systematic study on its petrogeochemical characteristics.The main understanding obtained is as follows:(1)The major elements and REEs of sandstone in various geochemical zones are not significantly different,indicating that the sandstone of the ore-bearing layer has a consistent material source.However,the contents of trace elements such as U and Re,Mo,Co,Cr,Pb,Zn,and Ni in the ores are significantly higher than those in sandstone of native red zone,weakly reducing zone,and moderately reducing zone,indicating that these elements were immigrated during the uranium mineralization period.These elements usually derive from deep reducing fluids with a certain temperature,further indicating that the ore-forming fluids may come from the deep part.(2)The content of kaolinite in gray reducing zone and ores is significantly higher than that in sandstone of native red zone,weakly reducing zone and moderately reducing zone.SEM analysis indicated that pitchblende was often adsorbed on the surface or in the micropores of kaolinite.Combined with the paleoclimatic characteristics of Yaojia period in the study area and the genesis of kaolinite,it was believed that the abnormally enriched kaolinite in gray reducing zone and ores was of epigenetic genesis and closely related to ore-forming fluids.The sandstone of the ore-bearing layer underwent acidic fluid transformation during the uranium mineralization period.(3)Combined with the uranium-rich hydrocarbon source rocks widely distributed in Jiufotang Formation and Shahai Formation of the Lower Cretaceous in Qianjiadian area,it was believed that the ore-forming fluids of the Hailijin uranium deposit might originated from deep uranium-rich reducing fluids.During the mineralization period,they exuded upward along the fault connecting the target layer of the lower member of Yaojia Formation.With the decrease of temperature and pressure,and the change of the environment from reduction to oxidation,the solubility of uranium in the fluid decreased sharply and precipitated,and finally accumulated into mineralization.This study provided a new idea for the genesis of sandstone-type uranium deposits in the southwestern Songliao Basin,which is of important theoretical and practical significance.
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