扬子板块北缘镇巴地区吴家坪组富Li-REE-Nb-V黏土岩地球化学特征及其地质找矿意义

Geochemical characteristics of the Wujiaping Formation Li-REE-Nb-V-enriched claystone in the Zhenba area, northern margin of the Yangtze Block and their geological prospecting significance

摘要:

沉积型锂矿主要产于黏土岩中，黏土岩的主微量元素可有效识别沉积物源及沉积环境。本文首次报道扬子板块北缘镇巴地区二叠系吴家坪组黏土岩锂、稀土、铌、钒等元素超异常富集的特征，基于详细的地球化学研究和区域地质资料，分析吴家坪组黏土岩的形成环境及沉积物源，并探讨扬子板块北缘锂、稀土找矿方向。研究表明，镇巴地区吴家坪组黏土岩产于晚二叠世，发育于吴家坪组与阳新组的平行不整合界面之上，代表了古风化壳沉积，黏土岩的Li2O最高品位0.39％，ΣREO（稀土氧化物总量）最高品位0.142％，V2O5最高品位0.26%，Nb2O5最高品位0.022%。主、微量元素地球化学特征指示黏土岩形成于咸化-半咸化海水相，氧化-还原过渡、碱性的沉积环境，对应于黏土岩化阶段。综合矿物学、地球化学、区域地质资料，认为研究区吴家坪组黏土岩来源于峨眉山大火成岩省的玄武岩，锂元素的富集与火山岩受流体交代-淋滤有关。扬子板块北缘广泛发育吴家坪组黏土岩，规模较大，锂、稀土、铌、钒综合成矿效果较好，找矿潜力巨大，应重点关注与沉积间断面有关的关键金属矿产，助力新一轮找矿突破。

Abstract:

Sedimentary lithium deposits are mainly produced in claystone, and the major and trace elements of claystone can effectively identify sedimentary provenance and sedimentary environment. This paper reports for the first time that the characteristics of super-enrichment of lithium, rare earth, niobium and vanadium in Permian Wujiaping Formation claystone in the Zhenba area, northern margin of Yangtze plate. Based on detailed geochemical studies and regional geological data, the formation environment and sedimentary provenance of the Wujiaping Formation claystone were studied, and the prospecting direction of lithium and rare earth in the northern margin of Yangtze Block was discussed. The study shows that the Wujiaping Formation claystone in the Zhenba area was formed in the Late Permian and developed on the parallel unconformity interface between the Wujiaping Formation and Yangxin Formation, which represents the deposition of ancient weathering crust. The highest grade in Wujiaping Formation claystone of Li2O, ΣREO, V2O5 and Nb2O5 is 0.39%, 0.142%, 0.26% and 0.022%, respectively. The geochemical characteristics of major and trace elements indicate that the claystone was deposited in the saline-salinized seawater facies, transitional oxidation-reduction and alkaline sedimentary environment, corresponding to the claystone stage. Comprehensive mineralogical, geochemical and regional geological data suggest that the claystone of Wujiaping Formation in the study area was derived from basalts in the Emeishan Large Igneous Province. The enrichment of lithium was related to the metasomatism and leaching of volcanic rocks by fluids. The northern margin of the Yangtze Block has widely developed Wujiaping Formation claystone, with a large claystone scale, good comprehensive metallogenic effect of lithium, rare earth, niobium and vanadium, and a huge prospecting potential. The critical metals related to the sedimentary discontinuity should be focused on, which will contribute to a new round of prospecting breakthrough.