Influence Mechanism Of Magma Intrusion On The Highly Enrichment Of Lithium And Zirconium In Coal

Lithium and zirconium are extremely important strategic key metal mineral resources in China.Coal is still the main part of China’s energy consumption structure,and there are widespread magmatic intrusions in the coal bearing strata of many coal mines worldwide and in China.However,there is currently little research on the occurrence and enrichment mechanism of lithium and zirconium in coal by magmatic intrusions.For this reason,this thesis systematically collected the coal rocks at different distances from the 2230 driving roadway of Tashan Coal Mine in Datong Coal Field to the diabase intrusion,analyzed the influence of magmatic intrusion on the content and occurrence of key metals lithium and zirconium in the coal seam,revealed the mechanism of the influence of magmatic intrusion on the high enrichment of key metals lithium and zirconium in coal,and obtained the following understanding:（1）The lithology and occurrence of magmatic intrusions in the study area were analyzed.The diabase intrusion in the 2230 driving roadway of Tashan Coal Mine in Datong Coalfield is taken as the research object.The occurrence of the intrusion is a dike（4.2m thick）.The mineral composition is mainly basic plagioclase,containing clay minerals and siderite.clay minerals were secondary products formed by pyroxene or feldspar alteration under hydrothermal metasomatism.（2）The impact of magma intrusion on coal quality in the study area were revealed.The coal rocks from near to far from the magma intrusion can be divided into three types:natural coke(R_o,max 3.59%-4.65%),thermal metamorphic coal(R_o,max 0.87%-1.89%),and normal coal(R_o,max 0.70%-0.76%).The intrusion of the dike leads to an increase in the degree of coal metamorphism near the dike,a decrease in coke slag adhesion,and an increase in ash yield;The intrusion of dike strongly alters the organic macerals in coal,resulting in the formation of a large amount of thermally altered components（such as pyrolysis carbon）in natural coke;The intrusion of dike leads to significant changes in the mineral composition of coal.The natural coke fractures and holes in the coal rock contact zone are filled with a large amount of dolomite.A large number of clay minerals are newly born in the coal 0.3m-3m away from the dike,and the mineral content in the normal coal far away from the dike is very small.（3）The impact of magma intrusion on the content of key metals lithium and zirconium in coal in the study area were clarified.Research has found that the lithium and zirconium contents in coal significantly increase with the decrease of distance from the rock wall,forming a highly enriched lithium zone within the range of 0.4m-7m from the rock wall,with an average content of 233.6μg/g,up to 467.6μg/g;A zirconium enrichment zone was formed within a range of 0.4m-2m from the magma intrusion,with an average content of 289.1μg/g,up to 293.2μg/g.There is a significant difference in lithium and zirconium content between contact metamorphic coal and normal coal:the average lithium and zirconium content in contact metamorphic coal is 187.3μg/g and 140.0μg/g,the lithium and zirconium content in normal coal is only 66.2μg/g and44.9μg/g.（4）The occurrence mode of key metals lithium and zirconium in the coal of the research area were clarified.Key metals Lithium and zirconium are closely associated.The content of lithium and zirconium has a significant linear positive correlation with the ash yield,mineral content,silica aluminate mineral content,clay minerals content,and kaolinite content in the coal,and the correlation increases gradually,indicating that kaolinite is the main carrier of lithium and zirconium in the coal in the study area.（5）The enrichment mechanism of key metals lithium and zirconium in the coal of the study area were revealed.The plagioclase mineral in diabase near the coal rock contact zone was altered into kaolinite mineral by acidic hydrothermal fluid,which is the main carrier of high content of lithium and zirconium.However,the content of lithium in diabase intrusion is only 6.46μg/g indicates that the high content of lithium in contact with metamorphic coal does not directly come from magma input.Near the intrusion,the content of lithium in kaolinite gangue is 408.3-734.4μg/g shows a decreasing trend step by step,which indicates that high temperature hydrothermal solution will lead to the activation and migration of some lithium in the kaolinite gangue,and finally enriched in the feldspar altered kaolinite mineral in the form of adsorption.Both diabase intrusion and kaolinite gangue are rich in zirconium,with the contents of171μg/g and 290.2μg/g,both of which provide a material source for high concentrations of zirconium in the coal rock contact zone.The thesis includes 73 illustrations,24 tables,and 120 references.