Texture and geochemistry of magnetite from the Jinshandian deposit, eastern China: Implications for the formation of high-grade Fe ore in skarn system

Abstract

Iron skarn deposits represent significant sources of high-grade Fe ores, although the mechanisms underlying their efficient enrichment in Fe are not yet fully understood. To investigate the enrichment processes of Fe in the skarn system, texture and geochemistry of magnetite from the Jinshandian Fe deposit located in eastern China were analyzed. Disseminated, friable, and massive ore types are identified at Jinshandian. The friable ore is characterized by loose structure, with minimal or absent cementation minerals interspersed among subhedral to euhedral magnetite crystals. The magnetite at Jinshandian displays significant textural heterogeneity, highlighted by macro- and nanoscale inclusions. Overgrowth and dissolution-reprecipitation (DRP) textures were locally recorded in magnetite. Magnetite grains contains low concentrations of Ti and V, alongside relatively higher Mg, Si, and (Ca+) Al+Mn. Most magnetite grains fall within the skarn field when plotted on geochemical discriminant diagrams. These findings, in conjunction with robust geological evidence, suggest that the Jinshandian deposit originates from intense water–rock interactions. The trace elements in magnetite from the friable ore exhibit similarities to those in disseminated and massive ores, indicating that the friable ore likely formed through a structural softening process that removed soluble cementing minerals (e.g., anhydrite/gypsum and calcite) from the disseminated or massive ore. A comparative analysis of Fe skarn deposits in the Edong district suggests that multiple mechanisms, including accumulation, structural softening, DRP, and superposition processes, may have significantly contributed to the formation of high-grade Fe ores within the skarn system, despite the primary controlling factors varying from one deposit to another.