云南宣威晚二叠世末生物灭绝期C1煤的地球化学特征

Geochemistry of the C_1 Coal of Latest Permian during Mass Extinction in Xuanwei,Yunnan

云南宣威雁塘煤矿晚二叠世末期C1煤层蕴含了二叠纪—三叠纪界线事件演化以及宣威肺癌高发原因方面的重要信息。本文对该矿C1煤层(包括三个分层——B1、B2和B3)进行了刻槽分层采样,采用X射线荧光光谱和电感耦合等离子体质谱测试了24个样品中常量和微量元素。利用偏光显微镜和带能谱的扫描电镜(SEMEDX)对煤中的显微组分及矿物组成进行微区分析,利用X射线衍射对低温灰化后的煤样作了矿物的半定量分析。结果表明,雁塘矿C1煤中常量元素Ca、Mn、Si含量明显高于中国煤均值;与华南二叠纪煤平均值、中国煤平均值、世界煤平均值以及地壳元素丰度相比较,雁塘矿C1煤中的W、Co、Mo、Cd、Pb、Be、Sb、Cu、Ni、Zn、Zr和V等12种微量元素相对比较富集。结合相关分析和SEM-EDX微区分析方法,对C1煤中微量元素的赋存状态进行分析发现Cs、Ga、Nb、Ba、Rb、Th、Tl、U与灰分显著正相关,表明这些元素主要以无机矿物态赋存,其它元素赋存状态复杂。结合C1煤中12种富集元素在垂向上的含量分布特征,推断Co、Cu、V、Zn应主要来源于峨眉山玄武岩风化产物;Be和Zr主要受同沉积火山灰影响;Ni则可能受峨眉山玄武岩风化及同沉积火山灰的共同影响;同沉积火山灰是C1煤中W来源之一;Sb可能受中低温热液的影响。C1煤中Zr与我国南方其他地区P/T界线粘土岩中Zr的富集规律一致。C1煤中富集的微量元素与宣威肺癌高发区可吸入颗粒物中的高含量元素一致,推断C1煤的燃烧可能与宣威肺癌高发有关。C1煤中富集的有毒有害微量元素可能与二叠纪—三叠纪之交生物大灭绝期的独特环境有密切关系。

The C1 coal in the Yantang Mine of Xuanwei, Yunnan Province, was deposited in the end of the Late Permian, and it is of great significance to reveal the mystery of the P/T Boundary event and the reason of the high lung cancer incidence. A total of 24 samples from coals, partings, roofs and floors of the C1 coal （including three sub-seams B1, B2, B3 in descending order） were collected using a channel-profile sampling strategy with vertical sampling space of 10 cm, and the major and trace elements were analyzed by X-ray fluorescence spectrometry and inductively-coupled plasma mass spectrometry. The mineral compositions were determined by optical microscope, scanning electron microscope equipped with energy-dispersive X- ray spectrometer （SEM-EDX） and X-ray diffraction analysis（XRD）. The results shows that, the contents of Ca, Mn and Si in the Yantang coals are higher than those in the Chinese coal averages~ W, Co , Mo, Cd, Pb, Be, Sb, Cu, Ni, Zn, Zr and V are enriched in the Yantang coals in comparison to Chinese coal averages and world coal averages. The ash-element correlation analysis and SEM-EDX analysis suggested that Cs, Ga, Nb, Ba, Rb, Th, TI and U are present as inorganic minerals, and other elements are present as complex occurrence. The vertical distribution of the highly enriched trace elements in three sub-seams B1, B2 and B3 indicated that Co, Cu, V and Zn were probably derived from the continental weathering of the Emeishan basalt, while the contents of Be and Zr were mainly influenced by the synsedimentary volcanic ash. In addition, Ni was probably influenced by both the continental weathering of the Emeishan basalt and the synsedimentary volcanic ash. Synsedimentary volcanic ash was one of the sources of W in the C1 coal. Sb may be influenced by medium-low temperature hydrothermal fluid. Enrichment of Zr in the C1 coal is consistent with that of claystones across the Permian-Triassic boundary in other areas of South China. Since enrichment of trace elements in the C1 coal of the Yantang mine are consistent with that of indoor PM10 from the high lung cancer incidence village in Xuanwei, these results support the conclusion that the combustion of the C1 coal was the main reason for the high incidence of lung cancer in Xuanwei. The enriched poisonous trace elements of the C1 coal may be closely related to the unique environment during mass extinctions at Permian-Triassic boundary.