Characteristics and genetic mechanism of Li-Nb-Ta enrichment in Late Permian coal in the coalfield of northwestern Guizhou,Southwest China
Critical elements area class of metals that are essential for modern technology but facing supply chain risks. Coal often exhibits enrichment in critical elements due to its high organic matter content,leading to the formation of coal-type critical element deposits under specific geological conditions. Many studies have demonstrated the enrichment of various critical elements in the Late Permian coal-bearing strata of Southwest China. However,the enrichment characteristics and formation mechanisms of these deposits are still unclear.This study focuses on the 9# coal seam of the Late Permian Longtan Formation in the Tailai coal mine,northwestern Guizhou. Systematic sampling of the coal seam,roof,and floor rocks was carried out to characterize the mineralogical and geochemical composition of the deposit. Mineral identification was performed using X-ray diffraction (XRD),while major and trace element analyses were carried out using X-ray fluorescence spectrometry (XRF) and an inductively coupled plasma-mass spectrometer (ICP-MS),respectively. XRD analysis revealed the predominance of kaolinite,quartz,illite,pyrite,anatase,rutile,calcite,dolomite,paragonite,and albite in the samples. Major oxide constituents include SiO2,TiO2,Al2O3,and Fe2O3. The trace elements Li,Nb,Ta,Zr,Hf,Sn,Th,and In exhibit significant enrichment. Concentrations of Li,Nb,and Ta exceed the world coal average by 7.9,7.8,and 8.7 times,respectively. Provenance analysis,coupled with an examination of mineral occurrence characteristics,suggests that medium volcanic rocks and high-Ti basalts sourced from the Emeishan region contributed to the material supply of the marine coal-bearing basin. Furthermore,post-depositional hydrothermal activity is inferred to have played a crucial role in the enrichment of critical elements in the 9# coal seam.
coalfield of northwestern GuizhouLate Permian coalscritical elementsLi-Nb-Ta enrichment
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