Flood basalt origin for Earth’s largest Paleoarchean banded iron formation

A genetic relationship between banded iron formations (BIFs) and flood basalts has long been assumed based on their close temporal and spatial association. However, proving causation has remained difficult given the absence of geochemical evidence, leading some authors to speculate that BIFs are not primary deposits. In this study, we examined the entire lithological succession of the western Iron Ore Group from the Singhbhum craton, which includes Earth’s largest, economic-grade BIF of Paleoarchean age. We show the Lower Lava flood basalts to plot on a Sm-Nd isochron with the conformably overlying Lower Shale, suggesting a 3.42 ± 0.10 Ga depositional model age for this iron-rich (average 18.26 Fe₂O₃ wt%, n = 7) clastic unit, implying it may be a precursor to the conformably overlying 3.39 ± 0.02 Ga BIF. This is the first occurrence of flood basalts being genetically linked to ferruginous shale on a Sm-Nd isochron and may support the hypothesis BIFs are products of secondary replacements of ferruginous clastic precursors. We assign a volcanogenic origin to this Algoma-type BIF and suggest its abnormally large size is related to the unroofing and weathering of the Lower Lava flood basalts during a major crustal formation event.