Distribution Characteristics and Enrichment Model of Germanium in Coal: An Example from the Yimin Coalfield, Hailar Basin, China

As a rare and dispersed element, germanium cannot form independent ore deposits but can be enriched in coal and sphalerite. The target of this research is the Cretaceous Ge-rich coal seam of the Yimin Coalfield in the Hailar Basin, which hosts the third largest coal-hosted germanium ore deposit in China. Based on X-ray diffraction (XRD) analysis and inductively coupled plasma-mass spectrometry (ICP-MS), the ash, volatiles, total sulfur, and trace elements in the germanium-rich (Ge-rich) coal samples and partings were identified. The contents of these components, combined with the affinity of the coal samples, in terms of the concentration coefficient of the trace elements and the distribution pattern of the rare earth elements, were considered to discuss the occurrence of Ge in the coal, the potential germanium ore-forming environment and the metallogenic model. The Ge concentration of this coal ranges between 28.1 and 135.5 ppm. Laterally, the content of germanium obviously increases toward the direction of the Ge source, which is the Ge-rich granite near the coalfield margin. The concentration of Ge in the coal is inversely proportional to the content of ash and directly proportional to that of sulfur and volatiles, indicating that the germanium is combined with organic matter in an adsorbed state in the coal seams. The enrichments of As, Mo, CS, W, and Hg in the coal seams are positively correlated with the Ge content, which is possibly controlled by hydrothermal fluids. According to the lateral and vertical distributions of Ge-rich drilling data and the geological factors affecting the enrichment of germanium, a possible source-migration-concentration model of the germanium coal-hosted ore deposits in the Yimin coalfield was established.