Origin of gray-green sandstone in ore bed of sandstone type uranium deposit in north Ordos Basin

Dongsheng sandstone-type uranium deposit is located in the northern part of Ordos Basin,occurring in the transitional zones between gray-green and gray sandstones of Jurassic Zhiluo Formation.Sandstones in oxidized zone of the ore bed look gray-green,being of unique signature and different from one of ordinary inter-layered oxidation zone of sandstone-type uranium deposits.The character and origin of gray-green sandstones are systematically studied through their petrology,mineralogy and geochemistry.It is pointed out that this color of sandstones is originated from secondary oil-gas reduction processes after paleo-oxidation,being due to acicular-leaf chlorite covering surfaces of the sandstone grains.To find out the origin of gray-green sandstone and recognize paleo-oxidation zones in the ore bed are of not only theoretical significance for understanding metallogenesis of this kind of sandstone-type uranium deposit,but also very importantly practical significance for prospecting for similar kind of sandstone-type uranium deposit.