| The Nantuozi Iron Deposit in eastern Hebei is hosted in the Yangshan Formation of the Neoarchean Luanxian Complex and constitutes a typical Algoma-type Banded Iron Formation (BIF) deposit in the North China Craton. Ore samples obtained from drill cores of the deposit were investigated via petrographic observation, whole-rock major and trace element analysis and iron isotope testing, to decipher its geochemical characteristics, source of ore-forming materials, paleosedimentary environment and features of late hydrothermal reworking. The results show that the ores mainly consist of magnetite and quartz, associated with gangue minerals such as plagioclase, biotite and hornblende; accessory minerals including calcite and pyrite are locally developed. Terrigenous clastic components are extremely low, demonstrating that the ores are typical chemical precipitates. After rare earth element (REE) normalization to Post-Archean Australian Shale (PAAS), all samples exhibit right-inclined REE patterns with light REE depletion and heavy REE enrichment, together with positive La, Eu and Y anomalies and insignificant negative Ce anomalies. The (La/Yb)N ratios are all less than 1, and Y/Ho ratios are generally close to the seawater endmember, indicating that the ore-forming fluids were dominated by seawater with a small amount of mixed submarine high-temperature hydrothermal fluids. All iron isotope δ56Fe values are positive. Combined with the lack of obvious negative Ce anomalies, it is inferred that the deposit formed in a generally anoxic marine environment, and iron materials underwent partial oxidation during mineralization. Combined with regional geological setting and geochemical signatures, mineralization of high-grade iron ore at Nantuozi Deposit was jointly controlled by sedimentary metamorphism and hydrothermal activity, and its metallogenic mechanism is highly consistent with the “remobilization and re-enrichment of iron”. This study can provide geochemical references for the research on metallogenic regularities of Neoarchean BIFs and regional prospecting in the Luanxian-Luannan ore concentration area, eastern Hebei Province. |
