Occurrence and genetic mechanism of pyrite in the No. 9 coal seam in magmatic erosion area of the Handan coalfield

The No. 9 coal of Yunjialing Coal Mine in Handan Coalfield, which is subject to obvious magmatic intrusion, is taken as the research object. Optical microscope observation, electron probe energy spectrometry (EPMA-EDS), X-ray diffractometer (XRD), X-ray fluorescence spectrometry (XRF) and other analytical tests were used to analyze the enrichment characteristics of whole sulfur, sulfur forms and minerals, to study the occurrence of sulfur and pyrite in the coals, and to explore the sources of different types of pyrite. The results show that the No. 9 coal of Yunjialing Coal Mine in Handan Coalfield is a high-sulfur coal (0.61%～7.12%), sulfide sulfur is the main form of sulfur in the coal (1.18%～4.90%), followed by organic sulfur (0.56%～2.16%) with a little sulphate sulfur (0.01%～0.06%). The No. 9 coal of Yunhailing coal mine was deposited in the transitional environment of sea and land phases, and seawater intrusion provided abundant sulfur source for the No. 9 coal seam, the gas-liquid materials brought about by neutral magmatism during the Yanshan period elevate the total sulfur content in the No. 9 coal of the Yunjialing Caol Mine, especially the total sulfur content of the upper coal plies are significantly higher than the total sulfur content of the whole coal seam. The microscopic occurrence of pyrite in the No. 9 coal mainly includes massive pyrite, disseminated pyrite and fissure-filled pyrite, and is characterized by multi-stage evolution. Massive pyrite is mainly formed in the early diagenetic stage, the high temperature and gas-liquid materials brought about by neutral magmatism during the Yanshan period modified the morphology of pyrite in the coal, resulting in the activation and recrystallization of pyrite in the coal into a massive fraction. Inorganic sulfur from the high-temperature-affected portion of the pyrite diffused into the surrounding coal body and sequestered as organic sulfur, increasing the organic sulfur content of the upper coal plies.