Study on Mesozoic magmatic intrusion and Paleozoic multi-mineral genesis mechanism in Huanghebei Coalfield，Shandong Province

Accumulation of various minerals is common in strata, especially in areas invaded by magma, which is more conducive to the generation and preservation of various minerals and greatly improves the exploration benefit and development value of mineral resources. Taking Huanghebei Coalfield in Shandong Province as an example, this paper studies the genesis mechanism of Mesozoic rock intrusion and Paleozoic multiple minerals(coal, coal-bed methane, coal-measure shale gas and rich iron ore). Research shows that: Huanghebei Coalfield Carboniferous-Permian Period tectonic conditions and sedimentary environment are conducive to the development of coal seam, and coal seam distribution in the plane is characterized by more in the east and less in the west, thinner in the east and thicker in the west, thinner in the north and thicker in the south, longitudinally has the feature of lower thicker and upper thinner. Coalbed methane reservoir has the characteristics of medium thickness of coal seam, wide distribution of coal grade, medium gas content, good adsorption, ultra-low undersaturation, low porosity and high permeability, underpressure and moderate buried depth. The coal-measure shale gas reservoir has the characteristics of thick mud shale accumulation, high organic matter abundance, medium hydrocarbon generation capacity, typeⅡ kerogen, medium maturity, low porosity and especially low permeability. Mesozoic magma intrusions into the limestone formations of the Majiagou Formation of Ordovician, and mineral-bearing hydrothermal metasomatism and magnetization occurred, forming a contact-metasomatism type rich iron deposit. Due to the intrusion of Mesozoic magmas and magmatic thermal metamorphism, the coal zonation centered on magmatic intrusions appeared in the overlying coal measures in the study area, and a large number of coalbed methane and coal-measure shale gas were produced and accumulated in local areas. The gas content, porosity/pore size, thermal evolution degree of organic matter and hydrocarbon generation capacity are negatively correlated with the distance from the intrusive body. Moreover, the closer the coal seam is to the intruder, the weaker the gas adsorption performance is, which is mainly in the free state. In conclusion, the magmatic intrusion in Mesozoic controlled the formation and coexistence of many Paleozoic minerals.