准格尔煤田老三沟外围勘查区煤系Al-Ga-Li-Nb(Ta)-Zr(Hf)共富集成因及资源潜力评价OA北大核心CSTPCD

The Permo-Carboniferous coal-bearing sequences of the Jungar coalfield,Inner Mongolia,exhibit significant enrichment of strategic metals,including Al,Ga,Li,and rare earth elements. This study investigates the enrichment mechanism of Al-Ga-Li-Nb (Ta)-Zr (Hf) strategic metal assemblages in these coal-bearing sequences,focusing on the Permo-Carboniferous coal-bearing sequence from the Laosangou peripheral exploration area. Systematic mineralogical and trace element geochemical analyses were employed,encompassing optical microscopy,X-ray diffraction (XRD),scanning electron microscope with energy dispersive spectroscopy (SEM-EDS),X-ray fluorescence spectrometer (XRF),a TIMA-X comprehensive mineral analyzer based on a Tescan Mira scanning electron microscope,and inductively coupled plasma-mass spectrometer (ICP-MS). The Taiyuan and Shanxi Formation coals in the Laosangou area display co-enrichment of Al-Li-Ga and Nb-Ta-Zr-Hf assemblages. In particular,concentrations of Li,Ga,and Zr in the entire coal seam,and those of Nb and Ta in specific sections of the main recoverable No.6 coal seam,reach levels that meet industrial utilization grades. This suggests significant metallogenic potential and value for development and utilization. The enriched Li and Ga in the coal exhibit a clear affinity for aluminosilicates,predominantly occurring in kaolinite and boehmite,and Li may also occur in chlorite. The enrichment of Al,Ga,and Li in the Taiyuan and Shanxi Formation coal-bearing sequence is a consequence of a complex interplay of geological processes. Firstly,weathering and denudation of Mesoproterozoic moyite in the Yinshan Oldland provide a primary source for Al,Ga,and Li enrichment. Terrigenous detritus derived from this source was initially enriched in the weathering crust of the Upper Carboniferous Benxi Formation,located in the northeastern part of the basin,serving as a direct material source of Al,Ga,and Li enrichment in the coal-bearing sequences. Secondly,fluid activity and water/rock interactions played a crucial role. Al,Ga and Li migrated along with groundwater and were subsequently deposited and enriched in the coal-bearing sequence. Lastly,the input of Li,Ga,Nb and Ta-rich intermediate-felsic alkaline volcanic ash,coupled with the migration of hydrothermal fluids,led to secondary enrichment of these elements in the studied coals during the coalification process.