Occurrence and origins of minerals in mixed-layer illite/smectite-rich coals of the Late Permian age from the Changxing Mine, eastern Yunnan, China

• Published in: International journal of coal geology 2012-11, Vol.102, p.26-34
• Main Authors: Wang, Xibo, Zhang, Mingquan, Zhang, Weiguo, Wang, Jumin, Zhou, Yiping, Song, Xiaolin, Li, Tian, Li, Xiao, Liu, Huidong, Zhao, Lixin
• Format: Article
• Language: English
• Subjects: Coal; Earth sciences; Earth, ocean, space; Eastern Yunnan; Exact sciences and technology; Geochemistry; Mafic magma intrusion; Mixed-layer illite/smectite; Sedimentary rocks; Soil and rock geochemistry; Stratigraphy
• ISSN: 0166-5162; 1872-7840
• DOI: 10.1016/j.coal.2012.07.010

Minerals in coals from the Changxing Mine of eastern Yunnan, southwestern China, were investigated using low temperature ashing plus X-ray diffraction (LTA+XRD), optical microscopy, and scanning electron microscopy with an energy dispersive X-ray spectrometer (SEM-EDX). The results show that minerals in the Changxing coals include mixed-layer illite/smectite (I/S), quartz, kaolinite, dolomite, Mg-bearing siderite, anatase, ammonium illite, K-illite, calcite, and chamosite, as well as minor amounts of hematite, paragonite, K-feldspar, and an Al-hydroxide mineral (gibbsite?). The Changxing coals are typically rich in mixed-layer I/S, accounting for an average of 47.2% in their low temperature ashes. Mixed-layer I/S occurs mainly in two types: (1) lentoid as thin beds, and (2) fractures- or cells-fillings. The Type 1 is of terrigenous detrital origin and probably related to the weathering products of the Emeishan basalt, while the Type 2 is of epigenetic origin and precipitated from hydrothermal fluids of a mafic magma intrusion. The high K and poor Na in the Type 1 mixed-layer I/S indicate that it is in a higher evolution stage than the Type 2. Ammonium illite, K-illite, and paragonite are probably products of dissolution and recrystallization of mixed-layer I/S, while Mg-bearing siderite and partly chamosite are related to the Fe, Mg, Al, and Si released from the evolution of mixed-layer I/S. ► Minerals in the Changxing coals are dominated by mixed-layer illite-smectite (I/S). ► Mixed-layer I/S occurs as lentoid (Type 1) and Fractures- or cells-fillings (Type 2). ► The Type 1 mixed layer I/S originates from the weathered remains of Emeishan basalt. ► While the Type 2 is related to hydrothermal fluids of mafic magma intrusion.