| The Carboniferous-Permian coal seams of Ningwu Coalfield,Shanxi are enriched with elements such as aluminum,lithium and rare earths,which is a potential favorable area for coal-type key metals.The enrichment of Al,Li and rare earth elements in the No.9 coal of Anjialing Coal Mine in Pingshuo mining area is controlled by terrigenous debris,but the reasons for the difference in the enrichment of Li and other key metals and the difference in element enrichment combination are not in-depth Systematic analysis.This article selects the Anjialing No.9 coal seam(including roof and floor and gangue)as the research object.Based on the theoretical knowledge of mineralogy,geochemistry and zircon chronology,comprehensive use of polarizing microscope,XRD,Raman,ICP-OES,ICP-Analysis and testing techniques such as MS and LA-ICP-MS are used to study the mineral characteristics,element content,distribution and chronological characteristics of Anjialing No.9 coal seam,and to explore the controlling factors of lithium enrichment in Anjialing No.9 coal seam.Get the following conclusions:(1)From the results of geochemical analysis,it can be seen that the content of Si O2,Ti O2,Ca O,P2O5 and Al2O3 in the Anjialing No.9 coal seam is relatively high.Judging from the vertical distribution map,the content of Si O2,Al2O3,Na2O,Ti O2,Fe2O3,K2O,Mn O and Mg O is high in the roof and floor of coal seams and gangue,while the content in coal is low.The content of Li in the Anjialing No.9 coal seam is the most concentrated in gangue,and its content is as high as 368ppm;the second is in coal and floor,the content is between20.00?266pm;the content in the roof is the lowest,and its content is 11.70ppm.The Li content and the loss on ignition(LOI)are obviously negatively correlated,indicating that Li is mainly stored in inorganic matter,and Li in the Anjialing No.9 coal seam is mainly affected by land-source control.Rare earth elements are enriched in coal and the total amount of rare earth elements in coal is higher than the content of gangue,indicating that rare earth elements are more likely to be enriched in coal;the distribution patterns of rare earth elements of all samples show a clear left-leaning trend.It is characterized by the enrichment of light rare earths and the loss of heavy rare earths.There is an obvious"V"shape at Eu,which means it is supplied by terrestrial debris;there is no obvious"V"shape at Ce,and Ce is basically normal.The ratio of main and trace elements such as Al2O3/Ti O2 and the diagram of main and trace elements such as Si O2-Ti O2 indicate that the type of parent rock of Li-rich and non-Li samples is mainly igneous rock,and there are some metamorphic and sedimentary rocks,but not rich in Li source rock.There are more sedimentary rocks added.Based on the structural background discriminant diagrams such as La-Th-Sc,Th-Sc-Zr/10 and DF(A-P)MT,it is determined that the provenance areas of Li-rich and non-Li-rich samples are consistent,and they are all Inner Mongolia uplifts with active continental margins.(2)XRD results show that the minerals in Anjialing No.9 coal and gangue are mainly composed of kaolinite,boehmite and calcite.The most stable mineral in coal and gangue is kaolinite.The average content of kaolinite in coal is 74.46%,and the average content of kaolinite in gangue is 77.57%.The main minerals in the top and bottom of the gangue are basically the same,and they are all composed of quartz,feldspar,muscovite,magnesite and kaolinite.The content of kaolinite in the top plate is the lowest,with a content of only 4.85%,while the content of kaolinite in the bottom plate is relatively high,with a content of 23.4%,which may be the cause of the enrichment of Li.The results of the laser Raman experiment show that the proportion of heavy minerals in the whole coal seam is different.Among the heavy minerals in the roof,the heavy mineral with the largest proportion is sphene,followed by zircon;the heavy mineral with the largest proportion among the heavy minerals in coal It is sphene,followed by biotite;the heavy mineral with the largest proportion of the heavy minerals in the gangue and floor is biotite,followed by sphene.The No.9 coal seam in the study area is dominated by a combination of stable and moderately stable heavy minerals.The combination characteristics of heavy minerals and heavy mineral characteristic indexes ATi and ZTR reflect that the source rocks in the study area are mainly acidic magmatic rocks and contain some metamorphic rocks and sedimentary rocks.Observing the clastic components of the coal roof and floor sandstone through a polarizing microscope,the results show that the clastic components of the coal roof and floor sandstone are mainly quartz and rock debris,followed by feldspar.Among the quartz particles,single crystal quartz is mainly used,and the types of single crystal quartz are mainly granite type single crystal quartz,part of metamorphic rock type single crystal quartz and sedimentary rock type single crystal quartz;relatively high degree of Li richness Dissolution harbor-like magmatic rock-type single crystal quartz is found on the bottom plate,while the top plate with low Li richness is not found.The type of polycrystalline quartz is mainly metamorphic rock type polycrystalline quartz;the type of cuttings is mainly igneous rock cuttings,followed by sedimentary rock cuttings and metamorphic rock cuttings.According to the composition and content ratio of sandstone clastics,it is reflected that the parent rock is mainly igneous rock,and contains a small part of sedimentary rock and metamorphic rock.According to Dickinson's Qt-F-L and Qm-F-Lt triangle diagrams,the source rocks of the roof and floor samples are mainly derived from the Inner Mongolia uplift,which is an orogenic belt.(3)The LA-ICP-MS chronological analysis of the detrital zircons in the roof and floor sandstones of Coal Seam No.9 shows that the age of the detrital zircons in the roof is mainly from the Late Paleozoic,accounting for 94%,and the age is between 322.6±7.2?292.7±7.1Ma,the main peak age is?302.9Ma;the precambrian age is2513±27?1896±36Ma,and the main peak age is?1919.9Ma,2029Ma and 2518Ma.The age of detrital zircon in the bottom plate is mainly from the Late Paleozoic,accounting for 82%,with an age ranging from 326.3±8.9 to 295.5±9.7 Ma,with a main peak age of?303 Ma;precambrian age ranging from 2525±28 to 1714±36Ma,the main peak ages are?1914Ma,2113Ma and 2479Ma.The CL images of zircons and Th/U ratio indicate that the zircons in the Late Paleozoic are magmatic zircons.The CL images of zircons and Th/U ratio indicate that the zircons in the Late Paleozoic are magmatic zircons.Based on the comparison of the tectonic background and the age spectrum of detrital zircons,it is believed that these zircons are mainly derived from the Inner Mongolia uplift on the northern margin of North China.However,the zircon with a peak age of?303 Ma among the floor detrital zircons may be derived from volcanic ash during the same period of the Inner Mongolia uplift.Later,due to the continuous southward subduction of the Paleo-Asian Ocean,the Inner Mongolia uplift was strongly uplifted with an age of?303 Ma The rock is lifted to the surface to provide detrital material for the roof of the No.9 coal seam.Combining the above-mentioned different analysis methods,it is shown that the source areas of the Li-rich and non-Li-rich sediments in the No.9 coal seam of Anjialing Coal Mine are not far away from Inner Mongolia uplift with the characteristics of recycle orogenic belts and active continental margins,but the source rock types Differences:1)The content of clay minerals in coal seams,gangues and floor with higher Li-rich degree is relatively high,which may lead to the enrichment of Li.2)The source rock types of Li-rich and non-Li sediments are mainly igneous rocks such as granite,and contain some sedimentary rocks and metamorphic rocks.However,there are more sedimentary rocks added to the source rock of the non-Li-rich sample,while the pozzolanic material is added to the source rock of the Li-rich sample. |
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