Occurrence characteristics and main control mechanism of trace elements in Early Permian coal in the southern margin of North China Plate

Abstract

Objective The study focuses on the development of critical elements in coal as a new area of mineral resource exploration. Methods Various analytical methods including X-ray diffraction, X-ray fluorescence spectrum, and inductively coupled plasma-mass spectrometry were used to investigate the mineralogy and geochemical characteristics of Early Permian middling coal in the southern margin of the North China Plate. Results The results indicate that the Early Permian coal in this region is mainly composed of minerals such as kaolinite, illite, tobelite, chlorite, and calcite, with SiO2, Al2O3, and CaO as the main elements. The coal seam samples also show enrichment of Li, with an average content of 76.83×10-6, as well as slight enrichment of Zr and Th. Other elements, such as Co, Zn, Rb, Cd, and Cs, are significantly depleted compared to the world average for hard coal. Conclusion Through correlation analysis and geochemical interpretation, it was concluded that the Li element in the Early Permian coal is mainly associated with clay minerals like kaolinite and is controlled by terrigenous debris. The uplift, weathering, and denudation of Mesoproterozoic K-feldspar granite and Carboniferous Benxi Formation palaeoweathering crust bauxite in the northern Yinshan ancient land, influenced by Variscan tectonic movement, became the primary source area for the Early Permian coal in the southern margin of the North China Plate. The salty and anoxic reducing sedimentary environment of the peat water medium favors the adsorption and deposition of Li by clay minerals, particularly kaolinite.

Keywords

• the southern margin of north china plate
• li element
• clay mineral
• coal
• sedimentary environment