Study On The Super-enrichment Mechanism Of Lithium And Niobium In The Upper Permian Heshan Formation In Pingguo,Guangxi

Lithium(Li),a critical metal,is an important energy metal.Niobium(Nb),a "superconducting metal",is widely used in emerging industries.Both are indispensable materialsrial for modern high-tech industry.In recent years,with the rapid development of new energy vehicles,superconducting materials,and other high-tech industries,the safe and sustainable supply of Li and Nb resources will face global challenges.Li and Nb resources are usually enriched in granitic and pegmatite deposits,but less in the sedimentary deposits,so they are generally not used as prospecting targets.However,with the discovery of supernormal enrichment of Li and Nb in karst(sedimentary)bauxite in southwest China,sedimentary deposits have become the hot spot of ore exploration.Due to the close relationship between lithium-rich clayrocks and weathering and deposition of basal carbonate rocks,and the fact that Li mainly occurs in clay minerals,this type of Li resource is defined as "carbonate clay type lithium deposit",which is a new type of Li resource in China.Nevertheless,the detailed occurrence form and supernormal enrichment mechanism of Li and Nb are still unclear,which hinders the evaluation,prediction,and comprehensive utilization of Li resources of this type.The study focus on the integration of new findings Li and Nb sedimentary rock on the upper Permian Heshan Formation in Pingguo,Guangxi,China,through the system of mineralogy,element geochemistry,detrital zircon chronology research,finding out the distribution of Li and Nb enrichment regularity,occurrence state,and sedimentary oreforming environment reveal the supernormal enrichment mechanism of the Li and Nb metallogenic model is established.The main understanding of this study is as follows:(1)The distribution and enrichment rules of Li and Nb were found out.Superenrichment of Li and Nb sedimentary rocks in western Guangxi are produced above the limestone ancient karst disintegration surface of the Middle Permian Maokou Formation,which is a part of the aluminiferous rock series in basal Upper Permian Heshan Formation.(2)The occurrence forms of Li and Nb were determined.The analysis of scanning electron microscopy(SEM-EDS),electron probe(EPMA),Li nuclear magnetic resonance(NMR),X-ray powder crystal diffraction(XRD),and the correlation between elements and minerals show that the carrier minerals of Li are mainly cookeite,while Nb mainly occurs in anatase.(3)The material source of the bauxite series is explored.Detrital zircon U-Pb dating shows a single age peak of ～260Ma,indicating that the bauxite series originated from volcanic rocks associated with Emeishan LIP or Permian magmatic arc at the same time.Zircon morphologies,trace elements,and geochemical characteristics of whole rock elements indicate that the provenance of the Nb-rich bauxite at the bottom and the Li-rich clayrocks at the top have changed dramatically,and the provenance from the Emeishan LIP and the Paleo-Tethyan Permian magmatic arc,respectively.There are two sources of bauxite,which are mainly felsic volcanic rocks of the Emeishan LIP and Paleo-Tethyan Permian magmatic arcs,including A1-type granite and basic syenite.However,the provenance of clays is peraluminous or moderately differentiated acidic rocks from the Paleo-Tethyan Permian magmatic arc.Nb is an inactive element,and most of it remains in anatase during weathering.Therefore,Nb is consistent with the source of niobium-rich bauxite and inherited from the felsic volcanic rocks of the Emeishan LIP and PaleoTethyan Permian magmatic arcs.The origin of Li and clayrocks may be different because Li is often abundant in moderately ate acidic volcanic materials,it is speculated that Li originated from acidic volcanic ash/debris in the Permian magmatic arc.(4)The sedimentary environment of the bauxite series is revealed.Mo,U,V,U/Th,B/Ga,and Sr/Cu ratios were used to trace the paleo-sedimentary environment.The results show that the bauxite series was formed by strong weathering and deposition under warm and humid climate conditions.The niobium-rich bauxite is formed in the depositional environment of cross-deviation reduction of the land-sea cross,while the lithium-rich clayrocks are formed in the depositional environment of a cross-deviatioxidation on of the land-sea cross.