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| Organic geochemistry were studied for the ores and altered, unaltered host sandstones at the Dongsheng sandstone-hosted uranium deposit in the Ordos Basin, North China. Interlayer alteration of the host sandstone in the Dongsheng deposit is different from one in the other sandstone-hosted uranium deposits of China and may be divided into four geochemical zones, i.e., the unaltered grey host sandstone in the reducing zone, light purple-red host sandstone in the oxidized zone, grey-green sandstone in the oxidized zone and mineralized grey sandstone (ore) in the oxic-anoxic transition zone. Uranium ore bodies occur, as tabular (mostly) and roll-front in shape, within the grey sandstone of unaltered reducing zone near oxic-anoxic transition zone for industrial mineralization and within the grey-green sandstone of oxic-anoxic transition zone for unindustrial mineralization. The gas chromatograms of total saturated hydrocarbons show unimodal distributions and the normal alkanes C17 to C35 with an odd carbon number preference and maxima concentrate around C25–29, which are typical for terrestrial high plant. The organic matter in the unaltered grey host sandstone and the light purple-red host sandstone in the oxidized zone is immature, while the organic matter in the re-reduced grey-green host sandstone and mineralized grey sandstone (ore) has a maturity equivalent to the main stage of petroleum generation (catagenesis). Evidence of hydrocarbon biodegradation associated with uranium mineralization was found. The biodegradation is a bacterial degradation which can be considered as a catalyst for the reduction of uranium. Occurrence of biodegraded migrated organic matter can be considered as a favourable criterion for the settling of uranium mineralization in searching and prospecting for uranium deposit. Finally, a two-stage genetic model of the uranium deposit based on the mixing of three fluids (brine, meteoric water and oil) has been developed. |
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| Keywords:Sandstone-hosted uranium deposit;organic geochemistry;Biodegradation;China |
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