Provenance Of Bauxite,and Occurrence State,enrichment Mechanism Of Associated Lithium In Ore-bearing Rocks Of Deposits In Nanchuan District,Chongqing

Lithium is one of the key elements indispensable for the development of strategic emerging industries in China.The lithium commonly associated with bauxite of the paleo-weathering crust sedimentary type.It is a potentially huge lithium resource pool and is one of the most important prospecting directions for sedimentary lithium mining exploration.In order to fully understand the bauxite mineralization process and the distribution characteristics,occurrence state and enrichment mechanism of lithium associated with the ore-bearing rock series,and enrichment the metallogenic theory of sedimentary lithium deposits,this paper focuses on Nanchuan bauxite of northern Guizhou-southern Chongqing,and carry out the field geological survey,mineralogy,whole rock geochemistry,micro area in-situ analysis,detrital zircon U-Pb and Hf isotope.The results show that zircons mainly crystallized from felsic magmas that were granitoid-derived related to orogeny/arc magmatism.The U-Pb ages range from Late Devonian to Archean?3054⁴06 Ma?,and they are divided into age groups:630⁴30 Ma,1251⁷32 Ma,1757¹405 Ma and 2553²409 Ma,clustering at 1251⁷32 Ma with the peak ages at 800 Ma and 1000 Ma.The zircon?_Hf?t?values vary from-15 to 10.The U-Pb age spectrum of detrital zircons from bauxite is consistent with that of Hanjiadian Formation and Huanglong Formation,indicating that the latter are the possbile source.By comparing the geological characteristics,zircon U-Pb ages and Hf isotopes from different strata in the South China Plate,I found that the Meso-Neoproterozoic feldspathic rocks from the western segment of the Jiangnan Orogen and the Nanling-Yunkai block of the Cathaysia Block are the most important source areas,while the western and northern margins of the Yangtze Block are less likely.The associated lithium deposits in the ore-bearing rock series are closely associated with bauxite.The long-term weathering-sedimentation of both bauxite and its ore-bearing parent rocks is the main enrichment mechanism of associated lithium.The dating results of detrital zircons indicate that the initial provenance area is not related to lithium enrichment.By contrast,the main factors to contral the Lithium enrichment containthe environment of weak oxidization-weak reduction,and continental,marine transitional facies where the?Palaeo?sea and land meet,the coastal marsh-lagoon tidal flat sedimentary system in the near-source area,the drying conditions of high salinity,and strong evaporation condition.In the ore-bearing rock series of bauxite,the lithium is mainly concentrated in the middle and upper parts,namely,the dense bauxite ore and the hard massive clay rock.In addtion,it is also concentrated in ferruginous rocks.The lithium enrichment exists in the top coal seam?line?,rather than the earthy bauxite layer.By comparison,the enrichment factors of Li are mainly shown by principal elements,which are closely related to Al and Si,but not to most other trace elements.In terms of minerals occurred,lithium is mainly related to clay minerals,especially kaolinite and illite.It has little correlation with diaspore boehmite.The concentration of lithium is influenced by the presence or absence of iron and the high or low valence state.The occurrence state of lithium is relatively complex.and the simple ion adsorption state of lithium in bauxite?rock?ore-bearing rock series is very few.Lithium mainly occurs in clay minerals and aluminum minerals in the form of metamorphic replacement.At the same time,the independent?clay?mineral of lithium cannot be completely excluded.In clay minerals,there may be heterovalent homologous substitution of Li⁺+A1³⁺?Si⁴⁺.Hydromica also exists Li⁺+A1³⁺?2Fe²⁺substitution series under suitable temperature and pressure conditions.In the early diagenetic stage,there may be a weak substitution of Li⁺+Mg²⁺?Al³⁺in the monohydrite.Li⁺mainly exists stably in the form of supplementing unfilled octahedral voids or hexagonal network centers.