山东黄河北煤田中生代岩浆侵入与古生代多矿产成因机制

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

  • 摘要: 地层中常见到多种矿产富集的现象,特别是有岩浆侵入的地区,更有利于多种矿产的生成和保存,大大提升了矿产资源的勘探效益与开发价值。以山东黄河北煤田为例,开展中生代岩浆侵入与古生代多矿产(煤炭、煤层气、煤系页岩气、富铁矿)成因机制研究。结果表明:黄河北煤田石炭–二叠系构造条件和沉积环境利于煤层的发育,平面上煤层分布具有东多西少、东薄西厚、北薄南厚的特征,纵向上具有下厚上薄的特征;煤层气藏具有煤层厚度中等、煤级分布广、含气量中等、吸附性好、特低欠饱和、低孔较高渗、欠压、埋深适中的特点;煤系页岩气藏具有泥页岩累积厚度大、有机质丰度较高、生烃能力中等、Ⅱ型干酪根为主、成熟度中等、低孔特低渗的特点;中生代岩浆侵入奥陶系马家沟组灰岩地层中,含矿热液与围岩发生接触交代作用和磁铁矿化,形成了接触交代型富铁矿床;中生代岩浆的侵入与岩浆热变质作用,使得研究区上覆煤系中出现了以岩浆侵入体为中心的煤类分带和局部地区煤层气与煤系页岩气的大量产生与成藏。煤层和泥页岩含气量、孔隙率/孔径、有机质的热演化程度和生烃能力与距离侵入体的距离成负相关关系,且煤层距离侵入体越近,气体的吸附性能越弱,以游离态为主。综上,中生代的岩浆侵入作用控制了古生代多种矿产的形成与共存。

     

    Abstract: 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.

     

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