黔西南普安矿区上二叠统底部煤层中锂的富集机理研究

Lithium is an important strategic mineral resource. However, the external dependence of lithium ore in China is high as 76% due to the resources endowment and less development of utilization technology for lithium from salt lakes. The newly discovered super-large coal-associated lithium deposits in north China have drawn much attention and proved that coal deposits could be considered as promising source of lithium. Previous research and the applicant’s unpublished data together show that the Late Permian coal in southwest Guizhou Province of China has a relatively high background value of lithium, indicating potential of coal-associated lithium resources. This research plans to take the lithium-rich coal seams that near the bottom of the upper Permian from Pu’an mining area, southwest of Guizhou, as the object. Physical and chemical mineral separation-enrichment methods, as well as determination techniques like microscope, XRD, XRF, ICP-MS, SEM-EDS, EMPA, LA-ICP-MS and MC-ICP-MS, etc., are to be adopted in the study for the purpose of conducting an in-depth investigation on coal petrology, mineralogy, and geochemistry, specifically revealing the modes of occurrence of lithium in coal and the temporal-spatial distribution of lithium in the upper Permian strata in the mining area. The origins of lithium-bearing mineral components and characteristics of elemental and isotopic source-tracing geochemical indicators will be discussed in detail. On the basis of above, regional structural activities, volcanic ash sedimentation and low-temperature hydrothermal ore-forming process in the area will be studied comprehensively to determine the dominant role that influence the lithium accumulation in the coal, and as a result, the enrichment mechanism will be proposed.

锂是重要战略资源，但我国受资源禀赋及开发技术限制，锂矿原矿对外依存度高达76%。近年来，山西、内蒙等地发现超大型煤伴生锂矿床，证明煤矿可能成为锂资源的潜在来源。前人研究及申请人测试数据均表明黔西南地区发育的晚二叠世煤中锂背景值显著偏高，显示一定的潜在伴生资源前景。拟选取黔西南普安矿区上二叠统底部富锂煤层为研究对象，借助矿物分离-富集实验手段，采用镜下鉴定、XRD、XRF、ICP-MS、SEM-EDS、EMPA、LA-ICP-MS 及MC-ICP-MS等分析技术，对煤样及顶、底板和岩石样进行煤岩学、矿物学和地球化学研究。在查清锂在普安矿区上二叠统含煤地层的时空分布规律及锂的赋存特征基础上，根据煤中富锂矿物质成因及具有物源示踪意义的元素与同位素地球化学信息，综合考虑沉积环境、构造背景、火山灰沉积及低温热液成矿活动对煤层元素聚集的影响，确定煤中锂超常富集的主控因素，阐明锂的富集机理。

研究选取黔西南普安矿区上二叠统底部富锂煤层为研究对象，通过矿物分离-富集实验及多种现代仪器分析测试，对矿区煤系地层进行了煤岩学、矿物学和地球化学性质研究，查清了煤中锂的丰度及赋存特征，综合揭示了煤层中锂的富集机理。研究发现普安矿区锂主要富集于矿区南部，20号煤层的灰基理论Li2O 含量达0.43%，显著超过了文献建议的可利用水平，具有较好的综合利用前景。此外，基于收集大量数据分析发现贵州晚二叠世煤中锂具有较高的背景值（1.89～142.15 μg/g，平均45.48 μg/g），识别出主要富集矿区为金沙、桐梓、正安、务川、普安、晴隆、兴仁等。研究发现普安 20 号煤中无机组分以黏土矿物为主，黄铁矿次之，少量方解石、石英。对煤样（Li含量134.09 μg/g）进行了可选性研究，精煤燃烧后煤灰中Li2O的理论含量可达0.26%，重力分选有利于后续从精煤燃烧产物或矸石中提取锂。Li与St,d、Fe、K、Na、Si和Ti呈正相关性，黏土矿物微区Li的含量范围为366~621 μg/g（平均421 μg/g）。逐级化学提取试验研究发现煤中水溶态、离子交换态、硅酸盐和铝硅酸盐结合态、碳酸盐结合态、硫化物的锂分别占20.96%、32.90%、22.80%、10.81%和3.92%。该煤中Li可能主要以吸附态赋存于黏土矿物之中。研究发现Li与Zr、Hf、Nb、Ta、In等元素显著相关，且Zr-Nb、Zr-Hf、Nb-Ta、Ta-Hf、In-Hf的相关系数分别高达0.98、0.99、0.99、0.98、0.99，显示极强的组合相关性。普安矿区各煤层总体上呈现重稀土富集特征，Er和Yb元素均呈较显著正异常，20、18、25号煤层的δEu平均值分别为1.22、1.21、1.15，均呈显著的正异常，3个煤层的δCe为0.95~0.97，Ce仅轻微亏损。综合分析认为普安煤层中Li与Zr、Hf、Nb、Ta、In等元素不来自正常沉积，煤中锂的异常富集可能由于火山灰沉积影响，且受成煤时期的沉积环境影响较小。研究结果为在该地区开展煤地球化学研究提供新的思路，为富锂煤层的分布规律研究提供科学参考，为煤伴生型锂资源的开发利用奠定了基础。