Effects of Rapid Igneous Intrusion Heating on the Geochemistry, Petrography, and Microcrystalline Structure of Coals from Huainan, China.

Abstract

Igneous intrusion into coal-bearing strata may change the geochemical, petrographic, and microcrystalline structural characteristics of coal. Here, a series of coal samples affected by igneous intrusion were analyzed by petrography, geochemistry, and X-ray diffraction. In addition, the trend observed in altered coal with normal burial maturity is compared to evaluate whether the intrusive coal follows another maturity path. A petrographic analysis shows that the R0 value increased rapidly and lost the ability to distinguish liptinite. Pyrolytic carbon and isotropic and anisotropic coke with a fine-grained circular mosaic structure are formed at the intrusion. Moreover, the degree of structural order of coal samples increases in an approach to the intrusion. There are transition phases with different structural orders due to different degrees of metamorphism. Petrographic and geochemical data indicate that intrusive coals may follow a maturation pathway other than that from normal burial maturation, which may be related to the rapid geological thermal event related to the intrusion. However, the results of XRD data suggest that the microcrystalline structure of igneous intrusion coals is consistent with a growth in the trend of normal burial. This study of geochemical petrography and microcrystalline structure of surrounding coal seams by rapid intrusive heating of igneous intrusions not only greatly improves the natural coke industrial utilization but also provides an important theoretical basis for the generation and enrichment of coalbed methane in igneous thermal abnormal coal reservoirs.