Sedimentary Control Of Lithium Enrichment In Permo-carboniferous Coals From Ningwu Basin, Shanxi, China

Lithium(Li)resources are of great strategic value for the high-tech development and national security.Coal seam is one of the geological carrier of lithium.Metallogenic theory of developing coal-type lithium is an important basis for comprehensive exploration,and utilization of coal-bearing mineral resources.The geochemical anomalies of lithium in Permo-Carboniferous coal in Ningwu Basin are remarkable.Based on the representative example,this thesis explored the concentration effects,geological control mechanism,and some new understandings are investigated.The existence of large coal-type Li deposits in the Permo-Carboniferous of Ningwu Basin was further confirmed based on the statistical data of more than 490 coal samples.The average content of Li in coal in the whole basin is more than 80 ?g/g.As the coal seam level was decreased,the content of Li increased.The Li content in the lower no.11 coal seam is four times that of the upper no.5 coal seam.The Li content of no.11 coal seam are higher in the top layer and the bottom layer,and lower in the middle part.Regionally,the lithium content in coal is generally high in the north and low in the south.The average Li content exceed 120 ?g/g in the northern 4,9 and 11 coal seams,and also exceeds 100 ?g/g in the western part in the south.The occurrence state and source of Li in coal of Ningwu Basin are revealed through the step-by-step chemical extraction experiment and analysis of structural geochemical.Li in coal is mainly presented in aluminosilicate minerals.Clay minerals are the major carrier of Li.La/Yb-REE analysis shows that the Li-bearing material in coal comes from the weathering and denudation of the bauxite of Benxi Formation in the surrounding area,originally from the Mesoproterozoic strata in the northern Yinshan paleo-land.Among them,Li-bearing minerals in Shanxi Formation coal are derived from granite and alkaline basalt,while Li-bearing minerals in Taiyuan Formation coal are mainly derived from calcareous mudstone and granite,predominated by sedimentary rocks.The geochemical mechanism of Li enrichment in coal of Ningwu Basin was revealed using simulating experiments combined with coal facies analysis of rock samples in the source area.It is found that the dissolution rate of Li increases with the decrease of p H value,indicating that it was possible to form a higher concentration of Li-containing solution only in strong acidic aqueous medium,which is suitable for peat marshes.Meanwhile,the enrichment of Li in the coal of Ningwu Basin may be related to the adsorption of kaolinite with the main format of ion exchanges.The Li content in coal varied periodically with the redox and salinity of peat swamp medium,revealing that the enrichment of Li in coal is intimately associated with the transgression process during coal accumulating period,and that Li is more easily enriched under the condition of strong reductive saline water.