Multiple parting bands within Permo–Carboniferous coal that are generally enriched in critical metals in the northern North China have been confirmed to be altered from volcanic ash (tonsteins). The tonsteins and adjacent coal in some areas contain boehmite with varying contents. Whether or not the boehmite has a relationship with the volcanic-ash-altered kaolinite remains poorly understood. Herein, petrographical, mineralogical, whole-rock geochemical, and in-situ elemental analyses, combined with U–Pb–Hf isotopic analysis of zircon, were performed for the boehmite-bearing/rich partings and coal collected from the eastern edge of the Datong and Jungar coalfields. Except for the boehmite, well-ordered kaolinite is predominant in the parting samples, where the columnar/tabular and vermicular kaolinite are commonly present. Additionally, the zircons separated from the representative parting and coal samples are mostly igneous origin with only one age population of ca. 300 Ma, almost same with the depositional age of the coal, suggesting that the kaolinite in the inorganic constitutes of the investigated coal seams were mainly altered from volcanic ash. Numerous fine-grained boehmite exhibit textural features of replacement for columnar/tabular and vermicular kaolinite along the cleavage cracks in the parting samples, suggesting that such boehmite were formed from desilication of volcanic-ash-altered kaolinite. The tonsteins and coal along the eastern edge of the coalfields were uplifted and influenced by fault activities due to Indosinian and Yanshan orogeny, which were probably experienced intensive leaching by silica-undersaturated percolating water and groundwater, resulting in desilication of volcanic-ash-altered kaolinite and precipitation of residual Al as boehmite. The Ga, preserved in the alumina octahedral sheets of volcanic-ash-altered kaolinite, were retained by boehmite due to its very similar geochemical behavior with Al. The formation of boehmite and its retention for Ga made a contribution to the genesis of high–Al–Ga coal in the northern North China.

华北北部二叠纪-石炭系煤中的多个分离带通常富含关键金属，已被证实是由火山灰（tonsteins）改变而成。一些地区的吨石和邻近煤中含有不同含量的勃姆石。勃姆石是否与火山灰蚀变高岭石有关系仍然知之甚少。本文对大同东缘采集的含勃姆石/富矿裂隙和煤进行了岩石学、矿物学、全岩地球化学和原位元素分析，并结合锆石的 U-Pb-Hf 同位素分析。和准噶尔煤田。除勃姆石外，分离样品中以有序高岭石为主，其中常见柱状/板状和蠕虫状高岭石。此外，从代表性分离样品和煤样品中分离出来的锆石大多是火成岩成因，只有一个年龄群体约为 100 。 300 Ma，与煤的沉积年龄几乎一致，表明调查煤层无机成分中的高岭石主要由火山灰蚀变而成。沿分离样品的解理裂纹，许多细粒勃姆石表现出柱状/板状和蠕虫状高岭石的替代结构特征，表明这种勃姆石是由火山灰蚀变高岭石脱硅形成的。煤田东缘的吨石和煤受到印支和燕山造山运动的断层活动的抬升和影响，可能经历了二氧化硅不饱和渗滤水和地下水的强烈淋滤，导致火山灰蚀变高岭石脱硅。以及残余Al以勃姆石形式沉淀。 Ga 保留在火山灰蚀变高岭石的氧化铝八面体片中，由于其地球化学行为与 Al 非常相似，因此被勃姆石保留。勃姆石的形成及其对Ga的保留对华北北部高铝镓煤的成因做出了贡献。