Study on coal petrology characteristics of contact metamorphosed coal from Carboniferous-Permian in Datong Coalfield

Large-scale igneous intrusions,seriously affected the coal mining process and coal quality. In order to study the Petrograpine characteristics of the conta ct metamorphosed coal,three diabase dikes and their alteration halos were sampled at three coal mines in Datong Coalfield. Vitrinite reflectance was measured and pro ximate and ultimate analyses were identified. Macroscopic and microscopic analyses were used to compare the differences of petrograpic characteristics between the u naffected coal and the contact metamorphosed coal,the macerals in contact metamorphosed coals were identified and quantitatively analyzed. Macerals were classified and their evolution process was discussed. The results show that the contact metamorphosed coal in Datong Coalfield has the vitrinite reflectance higher than 1.0% and its volatile matter yield is normally lower than 20%.The severely altered coal is immediately adjacent to the igneous intrusion or has the vitrinite reflectance higher than 2.0%,its macroscopic characteristics are significantly different from the unaffected coal,whiol can be divided into three types: massive coke,brecciated coke and granula 「coke. The slightly altered coal has the vitrinite reflectance ranging from 1.0%to 2.0%. No obvious macroscopic difference between the slightly altered coal and the una ffected coal was observed.macerals in the contact metamorphosed coal in Datong Coalfield can be divided into three types,namely remnants of original macerals,matrix of natural coke and newly formed components. The original macerals are unchanged/slightly altered vitrinite ,inertinite, and liptinite groups. The matrix of natural coke is mainly transformed by vitrinite and liptinite groups,which include mesophase spheres, mosaic structures ,and flow structures. The newly formed component is main pyrol ytic carbon. Macerals of the severely altered coal is dominated by matrix of natural coke,while the slightly altered coal mainly comprises remnants of original macerals.