A framework for REY transport and mineralization: Mechanisms in the early Permian no. 21 coal of North China

Coal, which can be enriched in rare earth elements and yttrium (REY), has garnered significant attention as a critical REY resource, especially given the global REY shortages and the rising costs of traditional mining. In this study, we examine the early Permian No. 2₁ coal seam in southern North China, a geologically complex coal-bearing region with a complex thermal evolution history. By comprehensively reviewing and analyzing geochemical and advanced nanoscale mineralogical observations, we investigate the processes of REY transport and mineralization.We emphasiz the significant roles of the infiltration of seawater and the exfiltration of groundwater composed of modified meteoric waters and influenced by hydrothermal fluids originating from deep magmatic processes. The results demonstrate that the interaction of these fluids forms geochemical barriers that promote the absorption of REY by clay minerals, significantly increasing the enrichment of REY. In addition to identifying sedimentary provenance, peat accumulation environments, and coalification as critical factors in REY accumulation, a comprehensive model for REY transport and mineralization is proposedthat categorizes the processes into three distinct types: (1) groundwater-dominated exfiltration, (2) seawater–groundwater interaction, and (3) seawater-dominant redistribution. These findings improve our understanding of REY transport and mineralization in coal seams. The proposed framework helps in the evaluation of coal as a potential REY resource and may guide future exploration in similar geological settings.