Zou Jianhua, Wang Hui, Chen Hongyu, Li Hang, Li Tian
School of Civil Engineering, Chongqing Three Gorges University, Chongqing 404020, China.
Chongqing Key Laboratory of Exogenic Mineralization and Mine Environment, Chongqing Institute of Geology and Mineral Resources, Chongqing 401120, China.
ACS Omega. 2022 May 26;7(22):18969-18984. doi: 10.1021/acsomega.2c02062. eCollection 2022 Jun 7.
Ammonian illite (NH-illite)-rich late Permian coals of high rank were discovered in southwestern China. This research reports new mineralogical and geochemical data of 11 bench samples from the adjacent Xingying mine, northeastern Chongqing Coalfield, southwestern China, with an emphasis on the modes of occurrence and origin of NH-illite. The Xingying coals, with low ash yields and medium sulfur, have a high rank (semianthrite, = 3.67%), owing to the plutonic metamorphism. Minerals in the coal consist of NH-illite and pyrite and, to a lesser extent, jarosite, albite, and anatase, with traces of chamosite, quartz, bassanite, apatite, fluorapatite, florencite, and rhabdophane. Compared with world hard coals, vanadium is significantly enriched with a concentration coefficient (CC) higher than 10; Mo and Pb are enriched (5 < CC < 10); F, Co, Ni, Cu, Ge, Se, Y, Zr, Nb, Ag, Cd, In, Sn, Cs, Sm, Eu, Tb, Dy, Er, Yb, Hf, Bi, and U are slightly enriched (2 < CC < 5) in the Xingying coals. Fluorine in host rocks, including roof, floor, and parting, is significantly enriched. Fluorine concentration in the coal may be increased greatly if the coal is mixed with host rocks during mining activity. Hence, the Xingying coals should be subjected to beneficiation before utilization for the environment and human health. The AlO/TiO and Eu anomalies demonstrated that the terrigenous materials come from the mafic basalts of the Kangdian Upland. NH-illite is formed by interaction of pre-existing kaolinite or K-illite with NH released from organic matter under high temperatures during the process of hydrothermal alteration. The authigenic chamosite, albite, quartz, anatase, apatite, fluorapatite, and rhabdophane are also deposited from the hydrothermal solutions. In addition, the Xingying coals are subjected to marine influences. Based on the preliminary evaluation, the Xingying coals cannot be a potential source for critical elements such as rare earth elements and yttrium. This indicates that not all the late Permian coals in southwestern China have economic significance for critical elements.
在中国西南部发现了富含铵伊利石（NH-伊利石）的高变质晚二叠世煤。本研究报告了来自中国西南部重庆煤田东北部相邻兴营煤矿11个煤样的新矿物学和地球化学数据，重点关注NH-伊利石的赋存方式和成因。兴营煤的灰分产率低、硫含量中等，由于深成变质作用，煤级较高（半无烟煤，挥发分Vdaf = 3.67%）。煤中的矿物由NH-伊利石和黄铁矿组成，还有少量的黄钾铁矾、钠长石和锐钛矿，以及微量的鲕绿泥石、石英、硬石膏、磷灰石、氟磷灰石、氟铈矿和钇磷灰石。与世界硬煤相比，兴营煤中的钒显著富集，富集系数（CC）高于10；钼和铅也有富集（5 < CC < 10）；氟、钴、镍、铜、锗、硒、钇、锆、铌、银、镉、铟、锡、铯、钐、铕、铽。镝、铒、镱、铪、铋和铀略有富集（2 < CC < 5）。包括顶板、底板和夹矸在内的围岩中的氟显著富集。如果在开采活动中煤与围岩混合，煤中的氟浓度可能会大幅增加。因此，为了环境和人类健康，兴营煤在利用前应进行选矿。Al2O3/TiO2和铕异常表明陆源物质来自康滇高地的镁铁质玄武岩。NH-伊利石是由热液蚀变过程中高温下原有高岭石或钾伊利石与有机质释放的NH4+相互作用形成的。自生鲕绿泥石、钠长石、石英、锐钛矿、磷灰石、氟磷灰石和钇磷灰石也由热液溶液沉淀而成。此外，兴营煤受到海洋影响。基于初步评估，兴营煤不是稀土元素和钇等关键元素的潜在来源。这表明中国西南部并非所有晚二叠世煤都具有关键元素的经济意义。
