Sm-Nd isotope study of chloroform bitumen in various energy minerals of the Ordos basin

Abstract：Sm-Nd isotope study has been performed on chloroform bitumen in oil, coal, uranium-bearing sandstone and its country rocks in the Ordos basin. The results indicate that the activity of fluids (including deep fluids) in the basin shows the multi-stage character, and that the late-stage fluid activity played a significant role in the formation of uranium deposits. Uranium-bearing sandstone bitumen, oil bitumen and coal bitumen in the same sequence of strata have the enriched mantle features, but they are not products of the same stage. A comparison between the coal bitumen in the Jurassic Zhiluo Formation of the Dongsheng field and that in the Jurassic Yan'an Formation of the Chengjiashan field in the southwest of the basin indicates that: there is appreciable difference in ages of the bitumen sources; the associated bitumen did not all form by thermal evolution of coals but might contain exotic fluids, and the associated bitumen in coals of the Zhiluo Formation was derived from an even deeper source than that in coals of the Yan'an Formation in the Dongsheng field. There is some internal genetic relation between the oil bitumen of the Zhiluo Formation in the Maling oilfield and the coal bitumen and oil bitumen in the coal bed of the Ya'nan Formation of Chengjiashan in the Ordos basin.