Behavior of Minerals and Trace Elements during Natural Coking: A Case Study of an Intruded Bituminous Coal in the Shuoli Mine, Anhui Province, China Xibo Wang,* ,†,‡ Yaofa Jiang, § Guoqing Zhou, § Peipei Wang, ‡ Ruixue Wang, ‡ Lei Zhao, † and Chen-Lin Chou ∥ † State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Beijing 100083, China ‡ College of Geoscience and Surveying Engineering, China University of Mining and Technology, Beijing 100083, China § Jiangsu Institute of Architectural Technology, Xuzhou 221116, China ∥ Illinois State Geological Survey (Emeritus), 615 East Peabody Drive, Champaign, Illinois 61820, United States ABSTRACT: The effects of thermal alteration by an igneous intrusion on the organic matter and inorganic constituents of a coal seam in the Shuoli mine, Anhui Province, China, have been investigated using reflected light microscopy, X-ray diffraction analysis (XRD), X-ray fluorescence spectrometry (XRF), inductively coupled plasma−mass spectrometry (ICP-MS), an electron microprobe, and a scanning electron microscopy system equipped with an energy-dispersive X-ray spectrometer (SEM-EDS). A total of 11 coal benches were collected from the profile (numbered as SI5-1 to SI5-11), all of which were found to be metamorphosed from a distance of 80 cm below the sill to the sill/coal contact; benches Sl5-8 to Sl5-11, which are in direct contact with the sill, were completely converted to natural coke. The maximum paleo-temperature inferred from R o,max of the natural coke is estimated to be 1000 °C. The minerals formed by the molten magma invasion are dominated by veins of mixed- layer illite/smectite (I/S). However, mixed-layer I/S of terrigenous origin is also present as lenses or thin layers. The mixed-layer I/S shows an increasing degree of illitization upward from the bottom. In addition to abundant mixed-layer I/S, the molten magma invasion also resulted in the precipitation of nontronite, albite, quartz, pyrite, and anatase, which mainly occur as fracture or pore fillings. Compared to the ash of the unaltered coal, the SiO 2 /Al 2 O 3 ratio (average of 1.4), and the percentages of K 2 O (average of 4.3%), Na 2 O (average of 0.8%), and Fe 2 O 3 (average of 3.2%) are higher in the ashes of altered coal and natural coke. The K 2 O and Na 2 O contents increase from the bottom to the top of the seam. Trace elements, including Be, F, Zn, As, Rb, Sr, Cs, Hg, Tl, Bi, Th, and U, exhibit a marked enrichment in the natural coke. Among these elements, the enrichment of Be, F, Rb, Sr, Cs, Th, and U is associated with the formation of molten magma-related minerals, such as mixed-layer I/S. High concentrations of Zn, As, Hg, Tl, and Bi in the natural coke are attributed to pyrite, which was related to the veins of mixed-layer I/S. The concentration of REY (rare-earth elements and yttrium) in the thermally altered coals is observed to be in the range of 267−980 μg/g (ash basis). The sill and all the coal samples are mainly characterized by a LREY-rich type (normalized to Cl- chondrite). The sill shows a typical europium anomaly with an Eu/Eu* value of 0.26. However, Eu/Eu* in the profile distinctly changes from weak negative to strong negative from the bottom of the seam toward the sill. The systematic fractionation change in Eu/Eu* in the profile is primarily attributed to changes in the nature of the intrusive molten magma. 1. INTRODUCTION There are many reports in the literature on thermal alteration of coal caused by igneous intrusions. 1−6 Intrusion of igneous rock elevates the degree of metamorphism of the coal near the contact and results in significant physical and chemical changes in the organic matter, including increased vitrinite maximum reflectance, elevated carbon content, decreased volatile yield, nitrogen and hydrogen contents, 2,7 reduced hydrogen isotopic exchange ability, and lower δ 13 C. 8 Mineralogical compositions of coal may also be affected by igneous intrusions. Minerals in coal can be altered or destroyed because of the heat, associated fluids, and gas derived from the igneous intrusion. 4,5,7 Ward et al. reported crystallographic and chemical changes in montmorillonite and kaolinite in a Permian coal of the Sydney Basin, Australia. 9 In addition, new minerals can precipitate from circulating hydrothermal fluids associated with the igneous magma. As well as these influences on the organic matter and minerals, enrichment or depletion of some trace elements may also be attributed to the igneous intrusion. 1,3,9−11 Chen et al. provided a useful review of the geochemical modification of trace elements in thermally altered coal. 5 Although most of these papers have discussed the effect of heat on the organic matter or inorganic constituents, little attention has been given to the effects of the intrusion composition on the development of newly formed minerals in the coal. This paper describes the effect of a felsic igneous intrusion on a low volatile bituminous coal of Permian age in the Shuoli mine, Anhui Province, China, and sheds lights on the origins of newly formed minerals and elevated abundances of some trace elements in the coal. Received: December 5, 2014 Revised: May 28, 2015 Published: May 29, 2015 Article pubs.acs.org/EF © 2015 American Chemical Society 4100 DOI: 10.1021/acs.energyfuels.5b00634 Energy Fuels 2015, 29, 4100−4113