Geochemical Characteristics and Influencing Factors of Germanium in Early Permian Coal from the Southern Margin of the North China Craton Basin: Constraints from Coal Petrology, Mineralogy, and Germanium Isotopes

Abstract The geochemical behavior of germanium (Ge) in Early Permian coal from the southern margin of the North China Craton remains unclear, and the enrichment mechanism of Ge under low-content conditions urgently needs to be elucidated. This study employed a variety of analytical techniques to conduct coal petrology, mineralogy, and geochemistry analyses on 16 Early Permian coal samples from the Huainan–Huaibei Coalfield on the southern margin of the North China Craton. The results show that the Ge content in coal ranges from 0.9 to 19.1 μg/g (average 6.33 μg/g, n = 16), generally at a low level. Ge content exhibits a significant positive correlation with vitrinite content, gelification index (GI), vegetation index (VI), and pyrite content, while showing a negative correlation with inertinite content, indicating that a reducing, water-saturated peat swamp environment favors Ge enrichment through organic matter complexation-adsorption and pyrite as a carrier. The δ74Ge values range from 1.85‰ to 3.52‰ and show a negative correlation with Ge content, confirming that organic matter preferentially incorporates the heavy isotope δ74Ge during Ge fixation. Both the Huainan–Huaibei Coalfield and the eastern United States coalfields are located in tropical-subtropical low-latitude humid climate zones, but due to the lack of intense synsedimentary hydrothermal activity and limited swamp development, Ge enrichment in the former is significantly lower than that in the Lincang Coalfield in Yunnan and the Wulantuga Coalfield in Inner Mongolia. The findings of this study provide a theoretical basis for understanding the geochemical behavior of Ge in coal from the Huainan–Huaibei Coalfield.