Geochemical characteristics and sedimentary environment analysis of trace elements in Carboniferous-Permian coal in Huozhou Area, Qinshui Basin

The moisture, ash, volatile matter, total sulfur and micro-components of the Carboniferous-Permian coal in Qinshui Basin were determined by industrial analysis and optical microscope, and the Qinshui Basin was analyzed by inductively coupled plasma mass spectrometry (ICP-MS). The content, distribution and geochemical characteristics of trace elements including rare earth elements in Carboniferous-Permian coal in Huozhou area of Qinshui Basin were analyzed. The depositional environment, paleo-salinity, redox environment and paleoclimate of coal-measure strata in the study area were explored using elemental geochemical parameters. The results show that the ash yield, moisture content, volatile matter and sulfur content of the coal in the central and southern Qinshui Basin are 11.19%, 1.02%, 14.02% and 1.27%, respectively. The rate is 1.14%, which is low metamorphic bituminous coal. Compared with Chinese coal, the content of trace elements in coal is depleted as a whole, only Cu(Cc=1.39), Sr (Cc=1.35) and Zr (Cc=1.04) are slightly enriched. The content of trace elements in coal of Taiyuan formation is slightly greater than trace elements in Shanxi coal. The distribution range of rare earth elements is 2.44-164.11 μg/g, with an average is 73.28μg/g, which is smaller than that of Chinese coal and slightly higher than that of world coal. The rare earth element Yb (Cc=2.81) in the thin coal is slightly enriched, Y (Cc=7.19) is enriched, and the rest are relatively depleted. The rare earth element distribution pattern is right-leaning "V" shape, which is a light rare earth enrichment type, with Eu negative anomaly and Ce weak negative anomaly, indicating that the source of rare earth elements comes from terrigenous debris, and seawater does not cause Ce loss. The average values of w(Sr)/w(Ba),w(V)/w(V+Ni) and w(Sr)/w(Cu) are 6.5, 0.74 and 7.57, respectively, indicating that the Carboniferous-Permian in the Huozhou area of Qinshui Basin as a whole belongs to a marine sedimentary environment, and the water environment is anoxic environment, the Carboniferous-Permian coal-forming environment is in a warm and humid climate. The average value of CaO/(MgO×Al2O3) in Shanxi Formation is 0.055, which is significantly lower than that of Taiyuan Formation's average of 1.55, indicating that the temperature has dropped from the Taiyuan Formation to the Shanxi Formation.