Geochemical Characteristics and Accumulation Rules of Coal in the Upper Permian Longtan Formation of Xinren Area, North Guizhou

This paper evaluates the coal quality in Late Permian on the basis of the Upper Permian coal samples’ main elements, trace elements, industrial analysis, sulfur and ash analysis data in Xinren area of North Guizhou. The focus is on the relationship between sulfur and ash in coal and coal-forming environment. The results show that the content of SiO₂, TiO₂ and K₂O is much higher, among which SiO₂ is 6 times higher than that of national average; TiO₂ is 7 times higher and K₂O is 10 times; the remaining oxide is 1 to 4 times of the average. In the normalized REE partition curve of coal chondrite of the upper Permian Longtan Formation of Xinren area, except the samples of PM403-MY3 and MY8, the REE distribution pattern in coal chondrite is similar, appearing a wide “V” curve with left high and right low. (La/Yb)_N is 5.27-18.34, with the average of 8.91 indicating the high fractionation of light and heavy rare earth elements. δEu is 0.38-1.52，the average being 0.74，with a significantly negative Eu anomaly. The coal resources in Xinren area are characterized by high total moisture, medium-high ash, low-medium-high volatility, ultra-low and low sulfur, low fixed-carbon, low phosphorus and ultra-low chlorine. In addition, ash yield in coal, composition index of coal ash and three-terminal analysis of ash composition all revealed that the coal-rich environment is from shallow water with strong hydrodynamics and weaker reduction in the land source area to deep water with weak hydrodynamics and strong reductive away from the land source area. This is consistent with the conclusion from the total sulfur analysis. The comprehensive analysis shows that the main geological factor of coal accumulation in Late Permian Xinren area is the tectonic movement, with Emeishan basalt, paleoclimate and sedimentary environment being some other factors.