沁水盆地二叠纪煤中稀土元素特征及碎屑物源区研究

Rare earth elements (REE) is immobile in most geology processes and always be used as a provenance tracer. It has been revealed that REE in some low metamorphic grade lignite coal fractionated and mobilized at some extent. In addition, although detrital matter in coal derives from rocks in source region, it probably only partly "copied" the information of source region due to sorting. Essentially, REE and other stable elements in coal reflect the information of detrital matter. Whether they can reflect the information of source region depends on the copying ability of detrital matter. In view of uncertainty of stability and indicating effectiveness of REE, and the potential influence of sorting on provenance study of detrital matter in coal, this research takes Permian high metamorphic grade anthracite coal from the Qinshui Basin as the research object, plans to investigate the category, occurrence and chemical composition of minerals in Permian coal from the Qinshui Basin, mainly through the use of low temperature ash and float-sink experiment, hand-picking and mountig minerals, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). By comprehensive use of the REE results of single mineral matter from LA-ICPMS, and the major, trace element and REE results of the bulk coal, this research also aims to reveal REE occurrence in coal, to illuminate distribution and occurrence characteristics of REE in the Qinshui Basin and to reveal the controlling factors on REE distribution, in addition, to further investigate the validity of REE as a detrital matter indicator. Besides, this research also attempts to summarize and compare the rules and features of certain indicators in coal, carbonaceous shale, shale and sandstone, in combination with the knowledge of source region, to illuminate to what extent the detrital matter in coal can trace the information of the source region.

REE因其性质稳定常用于源区示踪，但申请者曾发现在某些褐煤中REE存在一定的分异和迁移。此外，煤中碎屑物质虽来自源区，但“分选”作用可能使其仅部分继承源区信息。煤中REE本质上反映的是碎屑物质的特征，是否能反映源区信息，取决于煤中碎屑物质的继承能力。鉴于煤中REE在稳定性和指示效力上的不确定性，以及“分选”作用对于煤中碎屑物源区研究的潜在影响，本课题以沁水盆地二叠纪高煤阶无烟煤为对象，采用低温灰化-浮沉法、矿物挑选、XRD、SEM等手段，弄清沁水盆地二叠纪煤中矿物的种类、产状及化学组成。结合LA-ICPMS对单矿物REE的测试结果，以及煤中常量元素、REE等特征，揭示煤中REE赋存状态，阐明煤中REE分布特征及控制因素，探讨REE的稳定性及其对煤中碎屑物性质的反映效力。对比相关指标在煤、碳质泥岩、泥岩和砂岩中的规律，结合源区成分等信息，阐明“分选”作用对煤中碎屑物源区研究的影响。

稀土元素由于其特殊的地球化学性质和潜在的经济利用价值，一直以来受到国内外煤地质学家的高度关注。本项目运用煤田地质学、矿物学、元素地球化学、数理统计等理论知识，借助于光学显微镜、扫描电镜、XRD、逐级提取实验、浮沉实验等测试技术方法，在查明煤中矿物和元素特征的基础上，揭示沁水盆地山西组煤中稀土元素的赋存状态，阐明了煤中稀土元素配分模式特征及其控制因素，揭示了含煤岩系砂岩、泥岩、煤中稀土元素特征的差异及其对于源区示踪的影响。主要取得如下认识：（1）沁水盆地山西组煤宏观煤岩类型为半亮煤，显微组分以镜质组为主；（2）山西组煤主要以特低水分含量、低-中灰和特低-低挥发分产率为特征。垂向上，灰分产率自下而上呈逐渐减小趋势；（3）煤中矿物主要以高岭石，白云石，伊利石和石英为主，含少量黄铁矿和方解石。（4）煤中常量元素主要以SiO2和Al2O3为主，相比于中国煤均值，研究区煤中常量元素含量低于或与中国煤相似；（5）通过相关性分析、逐级提取实验、浮沉实验、煤中镜煤条带等手段发现煤中稀土元素主要赋存在高岭石、有机态和重矿物中；并且轻稀土与高岭石具更好亲和性，重稀土与有机质具更好亲和性。（6）由于机械分选、稀土元素的有机亲和性等原因，碎屑物源区相同泥岩、砂岩、煤中的稀土元素配分模式可能会呈现一定的差异性，因此在用稀土元素对含煤岩系沉积体系进行源区示踪时要谨慎。该项目的研究成果对于揭示煤中稀土元素的赋存状态、稀土元素碎屑物源区示踪效力、以及稀土元素机亲和性等方面具有重要理论意义。