Geochemical characteristics of hydrocarbons in ore-rich sandstones in the Qianjiadian uranium deposit, southwestern Songliao Basin

The formation of the Qianjiadian uranium deposit in the southwest of Songliao Basin is related to hydrocarbon charging and microbial reduction.However, the origin of oil and gas in the uranium deposit and the types of source rocks, sedimentary environment, maturity and potential multi-stage charging have not been thoroughly studied.The geochemical characteristics of hydorcarbons from adsorbed organic matter and inclusions in ore-rich sandstones were analyzed by means of off-line crushing extracting method and gas chromatography-mass spectrometry.The result shows that two types of hydrocarbons have light blue fluorescence emission color, suggesting similar compositions, and at least two stages of petroleum charge the uranium reservoir.The earlier charged petroleum was heavily biodegraded, showing large unresolved complex mixture (UCM)humps and a suite of C₂₆~C₃₀ 17α, 21β 25-norhopanes.The later charged petroleum was not or just slightly biodegraded, and biomarkers indicate that it was derived from the Lower Cretaceous Jiufotang Formation which was mature humic-sapropelic source rock deposited in a reduced and stratified semi-deep/deep lacustrine.As part of the systematic work of studying biogenic and petroleum-related uranium mineralization in sandstone-hosted uranium deposit, this result is of great significance to improve the research system, and is also helpful to multi-mineral comprehensive exploration such as oil-uranium co-exploration and coal-uranium co-exploration.