Mechanism Of Lithium Enrichment In Carboniferous-Permian Coals In Yuzhou Coalfield,Henan Province

With the increasing demand for lithium resources,the global research on lithium deposits and associated lithium minerals is gradually increasing,and lithium resources still mainly rely on traditional lithium deposits,serious shortage of supply and demand,the discovery of lithium rich coal is of great significance for easing the tension of demand for lithium resources in China and improving the dominance of Lithium price in China.Therefore,it is of great significance to study the geochemical characteristics of elements,source and enrichment mechanism of lithium in li-rich coal.This paper takes taiyuan Formation li-rich coal and Benxi Formation bauxite in Zhutougou Mining area of Yuzhou Coalfield,Henan province as research objects.Major elements,trace elements and Li and Sr-Nd isotopes were determined by X-ray fluorescence spectrometry(XRF),inductively coupled plasma mass spectrometry(ICP-MS)and multi-receiver inductively coupled plasma mass spectrometry(Mc-ICP-MS),respectively.In this paper,the contents and enrichment characteristics of normal and trace elements in coal and the indicative significance of related element geochemical parameters to coal forming environment are studied.According to the chemical extraction results of Li in li-rich coal and the correlation coefficient of Li with Al₂O₃and SiO₂,the occurrence state of lithium in coal was analyzed.The provenance of lithium in coal was determined based on the geological background and the geochemical characteristics of Li,Sr and Nd isotopes in coal and bauxite.Compared with the background values of the major elements in Chinese coal,it is found that the oxides of the major elements in the coal in this study are slightly enriched in K₂O(CC value is 4.64),and slightly depleted in Mg O,TiO₂and Na₂O(CC value is 0.17,0.46 and 0.07,respectively).The content of other oxides was within the normal range(0.5 Compared with the mean values of trace elements in Coal in China and the world,the contents of Li are the highest(CC value 32.52),while the contents of Tl,Mo and U are slightly higher(CC value 9.47,8.29,7.42).The contents of Ba and Bi were slightly lower than the mean value(CC value was 0.13 and 0.0.19,respectively),while the contents of other elements were within the normal range(0.5<CC<2)The main elements(Fe₂O₃+CaO+MgO)/(SiO₂+Al₂O₃)ranged from 0.15 to 1.84,and the average value of Al₂O₃/TiO₂was 54.2.The sedimentary environment of the fault was peat swamp with sea and land interaction,and the source rocks were mainly acidic magmatic rocks.The weathering degree of bauxite decreases from the top to the bottom according to WIG index.The ratios of V/Zn(0.24?8.3,mean 2.54),Sr/Cu(0.65?12.86)and V/(V+Ni)(0.34?0.91)were used to determine that the sedimentary environments during the coal-forming period were mostly Marine and continental transitional facies or Marine facies,mainly oxidizing sedimentary environment,but the bottom was a reduction environment.The climate of coal forming period is arid and humid alternately.In order to quantitatively explore the occurrence state of lithium in coal,the method of chemical extraction step by step was used to study and analyze lithium in coal.It is found that lithium in coal mainly occurs in acid insoluble phase(silicate,sulfide)(accounting for more than 97%),and the content of lithium in other phases is very little.Combined with the correlation between Li content and Al₂O₃and SiO₂content(0.82 and 0.80,respectively),it is speculated that Li in coal may also occur in coal mainly in the form of silicoaluminate.Li and Sr-Nd isotopic values in coal,bauxite and granite have been determined.The fractionation degree of lithium isotope?⁷Li in coal in the study area is relatively uniform,with little change in the whole coal seam.However,the fractionation degree of lithium isotope?⁷Li in bauxite of Benxi Formation varies greatly,and the fractionation degree of bauxite near the top is small,but gradually increases toward the bottom.The range of strontium and neodymium isotopes in the coal in the study area is basically the same as that in the bauxite of benxi Formation under the coal,and their average values are also very close.Therefore,according to the analysis of strontium and neodymium isotopes in the coal,it is believed that the provenance of the minerals in the coal is the bauxite of Benxi Formation exposed near the coal mine.It is proved that the source of lithium in coal is bauxite of Benxi Formation.