Iron Isotopes Applied to BIF-Hosted Iron Deposits

Abstract Published and unpublished iron isotope data from banded formations (BIF) their BIF-hosted hypogene (hydrothermal) ores the Quadrilátero Ferrífero (itabirites), Corumbá, Carajás districts in Brazil, as well Hamersley province Australia are presented discussed. BIF constitutes a typically thinly bedded or laminated chemical sedimentary rock, with ≥ 15% Fe layers of chert, chalcedony, jasper, quartz, whereas itabirite is considered laminated, metamorphosed formation rich oxides, which may contain carbonate minerals, amphiboles, abundant quartz. For Paleoproterozoic district, range δ 56 values similar to that BIFs, variations better distinguished different regional deformational domains. Light isotopic compositions dominate low deformation domain (δ = −0.42 ± 0.12 0.29 0.04‰), eastern, high-strain characterized by heavy −0.09 0.08 0.37 0.06‰; Mendes et al., Mineral Deposita 52:159–180, 2017). Iron composition for Neoproterozoic Corumbá region (hematitic, dolomite-rich: −1.83 −0.83‰; cherty-hematite: −0.49‰) controlled by: (1) primary seawater signature, (2) microbial activity, (3) supergene goethite alteration. Hydrothermal alteration reflected oxygen data, but apparently not fractionation. pairing shows increase, while 18 O decrease. In Archean jaspilites Carajás, tend display lighter than host counterparts. Also, there correlation between coupled clearer towards values, especially O. deposits, suggests direct both systems during low-grade, greenschist-facies metamorphism. On other hand, despite evident shift negative apparent preservation metamorphic ore hydrothermally modified show values. contrast, supergene-modified samples apparent. The (+1.24 + 0.44; one sample − 0.30‰) (+ 1.02 0.29‰) interval, reaching positive tendency lower (to 0.80‰). This review indicates application isotopes exploration presently limited mainly due restricted dataset available samples. Nevertheless, all local differences, general moderately deposits compared precursor BIF. strong imprint leads heavier As more become available, if these trends confirmed, use this tool be valuable future, instance decipher origin specific zones, consequence probable depth extension interpretation concealed, deep orebodies.