Microstructures of Coal and Their Relation with Gas Outhursts——A Case Study of the Yutianbao Coal Mine, Nantong, Sichuan

Outbursts of coal and gas are closely related to coal microstructures. Part of microstructures of coal areassociated with the coal-forming environments, but most of them are produced by tectonic deformation. In thispaper the types of microstructures of coal are distinguished according to the types and features of tectonicdeformations, which is convenient and can be easily employed by geologists. Based on the SEM study on coalpetrography of No.4 and No.6 coal seams of the Yutianbao coal mine, Nantong coal field, five types of coalare distinguished: nontectonic coal, microfissure coal, microcleavage coal, cataclastic coal and mylonitic coal.The microstructural features of various types are described in detail and their geological implications and rela-tionships with coal and gas outbursts are also discussed. Special mention is made of a series of the features ofplastic deformation of mylonitic coal. It is concluded that, other things being equal, the place with myloniticcoal is the most likely risk site for outbusts.The process and mechanism of coal and gas outbursts are suggested based on a series of changes inmicrostructures of the coal after bursting. In the process of gas outbursts, the plastic deformation issuperimposed by brittle deformation, thus ejecting large quantities of coal dust.