Effect of magma intrusion on pore structure and trace element migration of anthracite

Abstract Magma intrusion has an important influence on the physical and mechanical properties of coal and rock. In the area of magma intrusion, disasters such as gas outburst are prone to occur. Revealing its invasion law will be conducive to disaster management and energy development. For this purpose, changes in moisture, ash yield, volatile matter content, fixed carbon, mineral composition, major oxides, trace elements, and REE of coal under the thermal metamorphism of magma intrusion were analyzed. It is found that the moisture and volatile matter contents of the thermally affected coals in the mining face are generally lower than that of normal coals, while moisture and volatile matter contents are reduced towards to the magma intrusion contact. During magma intrusion, some minerals remain on the surface of the coal body, resulting in changes in the mineral composition of the coal body. The decrease in carbon atom net spacing, the increase in crystallite aggregation and ductility, and aromaticity in thermally affected coals have a positive impact on the improvement of coal metamorphism. Due to the influences of magmatic intrusion, the variation rules of major oxides in coal are different, and the closer to the magmatic intrusion zone, the easier the major oxides are to be depleted. However, magma intrusion will not lead to the loss of all major oxides in thermally affected coals, such as CaO and MnO contents are higher than unaffected coals. Most of the trace elements in the thermally affected coals of the No. 9 coal seam are depleted, while all of the elements Be, Cr, Ni, Tl, Pb, and U that are potentially hazardous to the environment are depleted. The contents of REE are low on the whole coalbasis, and the distribution pattern towards to magmatic intrusion shows a wide and gentle “ V ” curve with left high and right low, showing the characteristics of enrichment of LREE.