Geochemical characteristics of coal seam roof and floor elements in Xixian region of eastern Ordos Basin

The coal seam roof and floor cores of the Late Paleozoic Taiyuan Formation and Shanxi Formation in Xixian region of eastern Ordos Basin were systematically collected and analyzed.The high resolution ICP-MS method was used to describe the characteristics of major elements and trace elements about samples.The results show the samples are of higher quantity of SiO₂, Al₃O₂ and total rare earth element content, and the sedimentary environment is proved to be in transitional faces.Meanwhile, the oxidation sensitivity indexes Ni/Co, V/Cr and U/Th reflect oxidation conditions.Considering single layer, there are distinct geochemical differences between Taiyuan Formation and Shanxi Formation.The elements of Taiyuan Formation samples are more complicated due to its changing depositional environment.Rare elements pattern of samples means the relative enrichment of light rare elements and an obviously negative Eu anomalies.The data of (La/Yb)_N-ΣREY indicate mixed source rocks.Comparison with Shanxi Formation samples shows simple source rocks including granite, mixture rocks of alkali basalt and granite; while Taiyuan Formation consists of calcareous shale, granite mixed with alkaline basalt, continental tholeiitic rock mixed with alkaline basalt and granite mixed with sedimentary rocks.Combined with the above, the provenance of Shanxi Formation and Taiyuan Formation are both northern Yinshan ancient land, while Shanxi Formation source rocks are Proterozoic granite and alkaline basalt; Taiyuan Formation corresponds to Upper Paleozoic sedimentary rocks with a certain amount of granite and igneous rocks.