Iron Enrichment\nMechanism in Granular Iron Formation\n(GIF) of the Wuzhiling Formation, Songshan Group, North China Craton:\nImplications for Metallogeny

The extensive Paleoproterozoic iron formations (IFs)\ndistributed\nacross the North China Craton serve as ideal proxies for understanding\nthe redox variations in paleo-oceans before and after the Great Oxidation\nEvent (GOE). Here, we present a comprehensive analysis of the lithofacies,\nmineralogy, and geochemical characteristics of the granular iron formation\n(GIF) within the Paleoproterozic Wuzhiling Formation of the Songshan\nGroup in the southern North China Craton. Our findings reveal that\nthe GIF represents a chemical sedimentary rock, precipitated within\na water column characterized by layered oxygen-depleted to suboxic\nconditions. The protolith sediments of the GIF in the Wuzhiling Formation\nare hypothesized to have comprised quartz-coated hematite microparticles,\nalong with precursor deposits of aragonite and hexagonal iron oxides,\ncommonly referred to as green rust. Mineralogically, the GIF is predominantly\ncomposed of quartz and hematite, with the iron content attributed\nto the weathering processes of continental crustal materials, the\ninfluence of low-temperature hydrothermal fluids, and the incorporation\nof iron from seawater. During the GOE, a pivotal transition in Earth’s\nhistory, the (Pr/Yb) ratios normalized to PAAS (Post-Archean Australian\nShale) standards exhibit increased dispersion, accompanied by a gradual\ndecrease in the Y/Ho ratios. These geochemical shifts suggest a pronounced\nalteration in the ancient marine environment, transitioning from a\nmonolithic reducing state to a more complex redox stratification within\nthe seawater after the GOE. In summary, this study contributes to\nthe reconstruction of paleo-ocean redox conditions around the GOE,\nproviding evidence for the re-establishment of Precambrian paleoenvironmental\nconditions.