Abstract: Host sandstones in Dongsheng and Qianjiadian deposits contain hydrocarbons inclusions and absorbed oils.The oils contain abundant 25-norhopanes and tricyclic terpanes,indicating that oils were heavily biodegraded.The host sandstones show intimate intergrowth of coffinite or pitchblende with secondary pyrite and carbonate cement.The pyrite is biogenic,as defined by low δ³⁴S values from -39‰ to 17‰,and from -44.5‰ to -31.40‰ in the Dongsheng and Qiajiandian deposit,respectively.The carbonate cement has carbon derived from petroleum oxidation as indicated by its δ¹³C values from -27.5‰ to 0.3‰,and from -21‰ to -4‰,respectively.The coffinite shows microorganism-like structure.Based on the data,we proposed that sulphate reducing bacteria alone or using other kinds of bacteria oxidized petroleum simultaneously and reducd sulphates and U(Ⅵ) to generate pyrite and uranium U(Ⅳ) deposits.