Characteristics of Magmatic Intrusions and the Influence on Coal Seams in the Chaigou Coalmine, Datong Coalfield

Extensive igneous intrusions in the northern Datong Coalfield have significantly altered coal seams. The Chaigou coalmine is an area in the Datong Coalfield that has been severely affected by igneous intrusions, yet it has remained a research gap to date. To more intuitively visualize the three-dimensional morphology of igneous rocks, investigate the differentiation laws of magma intrusion in multi-seam systems, and explore the thermal evolution characteristics of coal macerals, this study investigated diabase characteristics using borehole data, laboratory tests, and three-dimensional modeling. The samples were subjected to vitrinite reflectance measurements, proximate analysis, and ultimate analysis, as well as systematic observations of macroscopic coal petrological characteristics and microscopic maceral characteristics. The differences in coal petrological parameters between normal coal and contact-metamorphosed coal were identified and statistically analyzed. On the basis of summarizing and classifying the maceral types, the evolution and identification of macerals in the contact-metamorphosed coal were discussed. Results indicate diabase was primarily intruded as multilayer sills along coal roofs and weak planes. The intrusion covers over 95% of the area. Magma preferentially invaded the Upper Carboniferous–Lower Permian Taiyuan Formation #5(3+5) coal seam, causing maximum impact with a cumulative thickness of 8.31 m. Intense contact metamorphism increased vitrinite reflectance (Ro,max) to 3.05%–3.85%. The coal exhibits high ash and low volatile matter. Microscopic observations reveal significant thermal evolution in macerals. Vitrinite transforms into anisotropic structures, while liptinite vanishes completely. Neo-formed high-temperature components are generated, including mesophase spheres, mosaic structures, and pyrolytic carbon. This study provides an important reference for three-dimensional geological modeling, differentiation laws of magma intrusion in multi-seam systems, and coal mine safety production in coalfields affected by igneous intrusions under similar geological conditions.