Formation age and tectonic setting of the Shirengou Neoarchean banded iron deposit in eastern Hebei Province: Constraints from geochemistry and SIMS zircon U–Pb dating

The Shirengou iron deposit, a typical BIF deposit located in eastern Hebei province in the North China Craton, is hosted in Neoarchean metamorphic rocks. The metamorphic rocks include hornblende plagiogneiss, plagioclase amphibolite and magnetite quartzite. We use contents and ratios of major elements for protolith reconstruction, showing that protoliths of the hornblende plagiogneiss and plagioclase amphibolite should be dacite and basaltic andesite, respectively. Based on geology and geochemistry of the hosting rocks, we infer that the Shirengou BIF is an Algoma type deposit formed in an arc-related basin in the Neoarchean. Constrains from SIMS U–Pb dating and oxygen isotopic analysis of zircon from wall-rocks and interlayer of the Shirengou iron bodies can be summarized as follow: (1) igneous zircons from two samples of amphibolite and gneiss yield U–Pb ages of 2541 ± 21 Ma and 2553 ± 31 Ma, respectively, providing the age of the Neoarchean protolith. Because the Shirengou BIF is an Algoma-type deposit, determined U–Pb age (2541–2553 Ma) for zircons from hosting volcanic rocks can constrain the BIF-forming time. (2) Metamorphic overgrowth zircons from amphibolite and gneiss give two U–Pb ages of 2512 ± 13 Ma and 2510 ± 21 Ma, respectively, corresponding to the Neoarchean matemorphism. (3) The zircons with δ18O values of 5.9–7.6‰ also indicate magmatic origin. The zircons have δ18O values of 6.8–9.9‰, suggesting that exotic high δ18O fluids were involved during metamorphism. Based on the geology and geochemistry of BIF, and combing with zircon age and oxygen isotopic systematics, we suggest that the Shirengou iron deposit was formed in a submarine volcanic setting related to subduction of an oceanic slab.

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► The Shirengou iron deposit is an Algoma type BIF deposit hosted in meta-volcanic rocks.
► The iron deposit was formed in an arc-related basin in the Neoarchean.
► Zircons U–Pb age (2541–2553 Ma) can constrain formation time of the Shirengou BIF deposit.