Transformation of minerals at the boundary of magma-coal contact zone: case study from Wolonghu Coal Mine, Huaibei Coalf
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Transformation of minerals at the boundary of magma-coal contact zone: case study from Wolonghu Coal Mine, Huaibei Coalfield, China Xing Chen1,2 • Liugen Zheng1,2 • Yalin Jiang1,2 • Chunlu Jiang1,2
Received: 28 December 2019 / Revised: 27 March 2020 / Accepted: 30 September 2020 The Author(s) 2020
Abstract Mesozoic and Cenozoic magma activity in the Wolong Lake mining area of Huaibei is frequent, and the degree of magma intrusion into coal seams remarkable. On the one hand, magma intrusion affects the utilization of coal resources; on the other hand, the macro and trace elements in coal are redistributed to form new mineral types. This study uses the Wolong Lake magma intrusion coal seam as a research object. The mineral paragenesis for igneous rock, coke, and thermally-altered coal in an igneous intrusion zone is studied using SEM, XRD, and Raman spectroscopy. During igneous intrusion, the temperature and pressure of igneous rock metamorphose ambient low-rank coal to high-rank coal and coke. The response mechanism of minerals and trace elements to magmatic intrusion is discussed. The results are: SEM analysis shows that ankerite and pyrite are formed from magma intrusion. Both minerals are strongly developed in the magma-coal contact zone, and less well developed in thermally-altered coal. ` XRD analysis shows that igneous intrusion strongly influences the types and content of minerals in coke and thermally-altered coal. In addition to the increase amounts of ankerite and pyrite, chlorite, serpentine, and muscovite, and other secondary minerals, are generated following igneous intrusion. ´ Raman analysis suggests that thermally-altered coal possesses the characteristics of both pyrite and coke. Coke from the magma-coal boundary zone possesses the typical characteristics of pyrite. Igneous rock contains a mineral similar to pyrite, confirmed by both having similar Raman peaks. The scattering intensity of Ag indicates that the formation pressure of pyrite increases from thermally-altered coal via the boundary between the coke zone and the igneous rock. Keywords Thermally-altered coal Mineral Igneous intrusion Raman spectroscopy
1 Introduction The intrusion of coal beds by igneous fluids is a common phenomenon in coal-bearing strata around the world (Kisch and Taylor 1966; Finkelman et al. 1998; Stewart et al. 2005). Igneous intrusion not only disrupts the continuity and integrity of coal beds, but also severely affects the industrial values of coal and the geochemical parameters of
& Liugen Zheng [email protected] 1
School of Resources and Environmental Engineering, Anhui University, Hefei 230601, Anhui, China
2
Anhui Province Engineering Laboratory for Mine Ecological Remediation, Hefei 230601, Anhui, China
organic and inorganic constituents in coal. These include the upgrade of the organic maturity and rank of coal, the reorganization of coal molecular and pore structure, the modification of methane-generation capacity, the transformation of minerals, and the enrichment and depletion of specifi
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