江西萍乐坳陷带新田煤矿关键金属铯的富集特征及成因机制

Enrichment Characteristics and Genesis Mechanism of Critical Metal Cesium in Xintian Coal Mine of Pingle Depression,Jiangxi,China

煤及其燃烧后的飞灰中能够富集关键金属,含量可以达到甚至超过传统的矿床类型,有望成为未来关键金属的主要来源。以江西萍乐坳陷带西段的新田煤矿为研究对象,运用扫描电镜-能谱(SEM-EDS)分析、TESCAN综合矿物分析(TIMA)系统、X射线荧光光谱(XRF)以及电感耦合等离子质谱(ICP-MS)等技术方法,开展煤岩学及岩石地球化学研究,旨在查明新田煤矿中关键金属的富集类型及其成因。结果表明:新田煤矿中的煤主要由有机质和高岭石组成,其次为石英、长石、伊利石,其余矿物包括少量的磁铁矿、透闪石、金红石和磷灰石。通过对比全球煤和全球沉积岩中关键金属元素的含量,发现新田矿区煤中主要富集关键金属铯,并在煤层及底板围岩中均可富集。关键金属铯的赋存状态可能是类质同象取代Rb和K进入长石晶格、类质同象取代伊利石中的K赋存在黏土矿物中或者和Li一起被黏土矿物吸附。结合新田矿区煤层和围岩的Al_(2)O_(3)/TiO_(2)值、稀土元素特征以及区域构造-岩浆活动历史,认为煤中关键金属铯富集可能为萍乡含煤盆地南缘古生代花岗岩风化形成的陆源碎屑来源,而燕山期富铯岩浆热液叠加改造作用有利于煤中关键金属铯的进一步富集。

Coal and its fly ash after combustion can be rich in critical metals,and the content can reach or even exceed the traditional deposit,which is expected to become the main source of critical metals in the future.Xintian coal mine in the western Pingle depression was taken as the research object,and the technical methods such as SEM-EDS analysis,TIMA system,XRF,and ICP-MS were used to carry out coal petrology and whole-rock geochemistry research,aiming at finding out the enrichment types and causes of critical metals in Xintian coal mine.The results show that the coal in Xintian coal mine is mainly composed of organic matter and kaolinite,followed by quartz,feldspar and illite,with slight magnetite,tremolite,rutile,and apatite.Compared with the contents of critical metals in global coal and global sedimentary rocks,Cs is considered as the main critical metal that is enriched in Xintian coal mine and can be enriched in the coal seams and floor surrounding rocks.The occurrence mode of critical metal Cs may be that isomorphism replaces K and Rb in the feldspar lattice,isomorphism replaces K in illite,exists in lattice of clay minerals or is adsorbed by clay minerals together with Li.Combined with the study on Al_(2)O_(3)/TiO_(2) ratios and the characteristics of rare earth elements with coal seam and surrounding rock in Xintian coal mine with the evolution history of regional tectonic-magmatic activity,it is considered that the enrichment of critical metal Cs in coal may be the terrigenous source formed by weathering of Paleozoic granite in the southern margin of Pingxiang coal-bearing basin,and the superimposition by later Cs-rich magmatic hydrothermal fluid in Yanshanian is beneficial to the further enrichment of critical metal Cs in coal.