Review on impacts of igneous intrusion in coal measures on coal texture

The igneous intrusion in coal measures resulted in a contact metamorphism of coal to form a natural coke or a thermally altered coal.Coal metamorphism by igneous intrusion reduces the value of coal, increases the risk of spontaneous combustion and gas outburst, worsens the trapping condition of coalbed methane, and is also considered as one cause forthe global climate change and mass extinction in certain geological history. To reveal the evolution of coal texture duringigneous intrusions, the impacts of igneous intrusion in coal measures on coal texture were systematically elucidatedfrom a macroscopic coalbed texture to the microscopic coal macerals and from the original sedimentary textures to the metamorphic features in this paper.Due to the high temperature, increased static pressure, and hydrothermal fluids during igneous intrusion, the texture and structure of coalbed and coal macerals werethermally altered. Moreover, the neo-formed textures, including fractures, devolatilization cavities and vacuoles, isotropy, anisotropy, pyrolytic carbons, graphitic spherulites, and coked bitumen, were developed.The evolution of coal texture caused by an igneous intrusion provides the scientific information about the aureole of contact metamorphism and the occurrence conditions of coalbed methane, and is of practical significance forthe safe and comprehensiveutilization of thermallyaltered coals.