Geochemical Responses Of Coal To Igneous Intrusion In The Huainan Coalfield

Coal is one of the most important energy resource in China. The Huainan Coalfield, as the biggest energy base in eastern China, where magma was widely intruded in coal measures in northern part. Safe coal mining, coalbed methane exploration and development were greatly influenced by igneous rocks. Thus, the study on geochemical responses of coal to igneous intrusion are of theoretical and practical significance.The microstructure, minerals, major and trace elements of sandstone, natural coke, igneous rock, sandy mudstone, and coal samples collected from a representative profile in the Huainan Coalfield were determined by optical microscope, powder X-ray diffraction, scanning electron microscopes with X-ray energy dispersive spectroscopy, X-ray fluorescence, inductively coupled plasma atomic emission spectrometry and mass spectrometry. The geochemical responses of coal to igneous intrusion in the Huainan Coalfield were discussed in detail.The characteristics of pore and fracture development, lithologic evolution, minerals deposition, major and trace elements variation in intrusive sill were investigated. The relation of the size of pore and degree of fracture development of natural coke to igneous rock, and the condition for coalbed methane storage and migration were elaborated. The impacts of igneous intrusion on moisture, volatile matter, sulfur, carbon, hydrogen, and nitrogen of coal were elucidated. In view of the vertical distribution and occurrence of minerals in the profile of natural coke, three stages of hydrothermal fluids, i.e., Ca, Mg, and Fe-rich, Si-rich, and Fe and H2S-rich, accompanying igneous intrusion in the Huainan Coalfield, were identified. Based on the minerals and concentrations of elements of various rocks, and its geochemical properties, the mechanism of chemicals exchange between intrusive igneous rock and coal was presented. Results indicated that Fe, Ca, S, Si, Mg, Zn, Cd, and Pb were carried into natural coke through hydrothermal fluids; the concentrations of Si, Co, and Ni in natural coke increased in correspondence with the rise of ash yields caused by contact metamorphism, while B in coal volatilized; Mn directly related to the intrusive magma; P, Ga, Ge, and Sr were brought into coal by groundwater, however, K, Na, and Ba were leached out.