Abstract:The BIF-type iron deposit at Sijiaying in eastern Hebei Province is considered one of the most representative banded iron deposits in China. A systematic investigation of ore and mineral characteristics holds significant implications for understanding the metallogenic evolution of BIF-type iron deposits. In this study, we conducted comprehensive petrographic observations on various typical iron ores from this mining area, and combined them with in situ electron probe (EPMA) testing and analysis, five distinct magnetite types were identified. Furthermore, we identified four stages of metallogenic evolution: the initial sedimentary stage, metamorphic deformation stage, hydrothermal alteration stage, and epigenetic oxidation stage. EPMA results were obtained for magnetite, biotite, chlorite, and hornblende. By analyzing the chemical characteristics of magnetite and calculating the different formation temperature of biotite and chlorite, and considering changes in the metallogenic environment indicated by their chemical characteristics, it indicated that a typical feature of sedimentary metamorphism is present in the early stage of the deposit and that it suffered from metamorphism, deformation, and hydrothermal effects in the later stage. Combined with geological features, petrographic characteristics of ore minerals and gangue minerals, major element analysis, and other studies, we considered that the oxidation after uplifting to the surface had less influence to the deposit; the enrichment of Fe may be related to the migration of elements such as Mg, Mn, and Ca. The end of the metamorphic deformation stage to the hydrothermal alteration stage is the most important stage for the formation of Fe-rich iron ore in the BIF-type iron deposit at Sijiaying in eastern Hebei Province.