织纳煤田龙潭组煤系富铌-稀土金属层地球化学特征及元素富集成因

Geochemical characteristics and genesis of element enrichment of niobium-rich-rare earth metal layer in Longtan Formation of Zhina coalfield

  • 摘要: 【背景】随着战略性金属需求的日益增长和传统金属矿床资源逐渐耗竭,煤及含煤岩系被认为是稀有金属的潜在来源,煤系共伴生已然成为当前矿产勘查的主要方向之一。黔西织纳煤田发现了一套富铌(Nb)、稀土元素(REE)的煤系,其Nb和REE含量分别高达334.89 μg/g和1014.51 μg/g,这一发现对煤系金属矿床理论研究具有重要意义。【方法】选取织纳煤田龙潭组煤系作为研究对象,采用工业分析、扫描电镜能谱(SEM-EDS)、X射线荧光光谱(XRF)和电感耦合等离子体质谱(ICP-MS)等测试手段,分析织纳煤田内富Nb、REE煤系的地球化学特征,深入探讨煤系关键金属元素的富集与成因。【结果和结论】(1)煤系属于低水分、低-中灰分、低挥发分、中-高硫的无烟煤;煤中矿物主要由黄铁矿、黏土矿物和石英组成,还发现了闪锌矿和锐钛矿;其中常量元素以SiO2和Al2O3为主,Fe2O3、MgO和TiO2的含量较高。(2)与中国煤、世界煤中微量元素均值相比,该煤系中富集了Nb、Ta(钽)、Zr(锆)、Hf(铪)和REE等关键金属元素。纵向上,所采煤层中9号煤层的关键金属元素最为富集;平面上,研究区关键金属元素含量具有自南向北逐渐增高的趋势。织纳煤田煤中稀土元素类型为轻稀土富集型,轻重稀土分馏程度高。同时,Eu和Ce元素的负异常表明,陆源供给较为稳定,且覆水深度变化不大。(3)通过对不活动元素和REE物源示踪分析,织纳煤田龙潭组煤系中关键金属富集的物质来源于康滇古陆的峨眉山高钛玄武岩和顶部中酸性岩的风化碎屑,还受到同沉积的碱性火山灰和长英质火山灰的输入影响。同时,煤中关键金属元素在物质来源和沉积环境等因素的共同制约下形成Nb(Ta)-Zr(Hf)-REY多金属矿化富集层。

     

    Abstract: Background With the increasing demand for strategic metals and the gradual depletion of traditional metal deposit resources, coal and coal-bearing rock series are considered to be potential sources of rare metals, and coal series associated has become one of the main directions of current mineral exploration. A set of coal measure strata rich in niobium (Nb) and rare earth elements (REE) has been found in Zhina coalfield, western Guizhou and the contents of Nb and REE are as high as 334.89 μg/g and 1014.51 μg/g, respectively. This discovery is of great significance to the theoretical study of coal measure metal deposits. Methods The Longtan Formation coal measures in Zhina coalfield were selected as the research object. Industrial analysis, Scanning Electron Microscope Energy Dispersive Spectrum (SEM-EDS), X-ray fluorescence spectroscopy (XRF) and inductively coupled plasma mass spectrometry (ICP-MS) were used to analyze the geochemical characteristics of coal-bearing strata rich in Nb and REE in Zhina coalfield, and the enrichment and genesis of key metal elements in coal-bearing strata were discussed in depth. Results and Conclusions (1) Coal measures belong to anthracite with low moisture, low-medium ash, low volatile and medium-high sulfur. The minerals in coal are mainly composed of pyrite, clay minerals and quartz, and sphalerite and anatase are also found. The major elements are mainly SiO2 and Al2O3, and the contents of Fe2O3, MgO and TiO2 are high. (2) Compared with the average trace elements in the world's coals, the coal-bearing strata are enriched in key metal elements such as Nb, Ta (tantalum), Zr (zirconium), Hf (hafnium) and REE. Vertically, the key metal elements of No.9 coal seam are the most enriched in the coal seam. On the plane, the content of key metal elements in the study area has a trend of gradually increasing from south to north. The type of rare earth elements in Zhina coalfield coal is light rare earth enrichment type, and the degree of light and heavy rare earth fractionation is high. At the same time, the negative anomalies of Eu and Ce elements indicate that the terrestrial supply is relatively stable, and the water depth does not change much. (3) Through the analysis of inactive elements and REE provenance tracing, the key metal-enriched materials in the coal measure strata of Longtan Formation in Zhina coalfield are derived from the weathered debris of Emeishan high-titanium basalt and top intermediate-acid rock in Kangdian ancient land, and are also affected by the input of co-deposited alkaline volcanic ash and felsic volcanic ash. At the same time, the key metal elements in coal form Nb(Ta)-Zr(Hf)-REY polymetallic mineralization enrichment layer under the common constraints of material source and sedimentary environment.

     

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