The Huoqiu iron ore field in north-west Anhui province is located in the south-east margin of the North China Craton and hosts large iron resources. Orebodies are hosted in Neoarchean amphibolite fades metamorphic rocks, forming silicon-iron bands from north to south. The area is dominated by an Early Precambrian basement consisting of Neoarchean grey gneisses, amphibolites and metasediments. The gneisses are similar with assemblages of Trondhjemite-Tonalite-Granodiorite in compositions and intercalated with amphibolites. Igneous zircons from gneisses and amphibolites have U-Pb ages of 2.86 and 2.75 Ga respectively, which are interpreted as the crystallisation ages of their protolith. Zircons from amphibolite and gneiss have epsilon_(Hf)(t) values of 2.4-15.5 and -3.0-1.5 respectively. The t_(DM2)(Hf) model ages of the gneiss range from 2.87 to 3.14 Ga, which is consistent with t_(DM1)(Hf) ages of amphibolite (2.84-3.16 Ga). The U-Pb-Hf isotopes thus confirm that the gneisses were generated by partial melting of amphibolite. Two granites produce two group Hf isotopic compositions. The older one (1916 ± 42 Ma) has epsilon_(Hf)(t) values and t_(DM1)(Hf) ages of -9.4-3.4 and 2.24-2.71 Ga respectively, whereas the younger one (1823 ± 41 Ma) shows a large variation in epsilon_(Hf)(t) values of -18.1-12.5 and t_(DM1)(Hf) model ages of 1.73-2.92 Ga. Geological and geochemical characteristics indicate that the Huoqiu banded iron formations are a Superior-type iron formation rather than an Algoma-type as previously considered.
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