Geology and Stable Isotope Geochemistry of the Biwabik Iron Formation, Northern Minnesota

Perry, Eugene C.; Tan, F. C.; Morey, G.B.

doi:10.2113/gsecongeo.68.7.1110

Cited by 140 publications

(52 citation statements)

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“…The most likely scenario is a largely simultaneous diagenetic or metamorphic formation of magnetite and siderite. Both would have formed from a common precursor substrate by the partial reduction of previously precipitated ferric oxyhydroxides by oxidation of organic matter (Han, 1978;Perry et al, 1973;Ewers and Morris, 1981;Lovley, 1991). Given that coexisting magnetite and siderite in the investigated sample show a uniform relative difference of ~0.9‰ and that this difference agrees with that expected from isotope equilibrium fractionation (see Table 5), the coupled formation under equilibrium conditions is suggested.…”

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 74%

“…Both fractionation factors are considerable higher than the observed difference which may either indicate that another process is involved or the formation of magnetite and iron carbonates occurred at an elevated temperature. Alternatively, magnetite and siderite might have formed by abiotic reduction of ferric (hydr)oxides by oxidation of organic matter during late diagenesis or low-grade metamorphism (Perry et al, 1973;Morris, 1993;Frost et al, 2007). Predictions from Mössbauer data (Polyakov and Mineev, 2000;Mineev et al, 2007;Polyakov et al, 2007) give an equilibrium fractionation factor ∆ siderite-magnetite between -1.8 and -2.8‰ at 22°C which decreases to -0.8 to -1.2‰ at 200°C (Table 5).…”

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%

“…Further pathways involve the abiotic reduction of Fe(III) (e.g. Perry et al, 1973;Morris, 1993). Alternatively, magnetite incorporates hydrothermal Fe(II) (Ohmoto, 2003).…”

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%

“…The Fe(II) released by reduction reacts either with residual ferric (hydr)oxides to produce magnetite or with bicarbonate to form siderite. Several studies of C isotope compositions in Precambrian BIFs indicate that extensive magnetite and iron carbonate deposition resulted from organic carbon oxidation coupled to Fe(III) reduction (Perry et al, 1973;Walker, 1984;Baur et al, 1985;Kaufman et al, 1990). In this process, layering is of diagenetic origin that is controlled by the relative amount of organic matter to ferric (hydr)oxide in a given layer.…”

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%

“…The investigation of light stable isotope systems in BIFs, namely O, C and S isotope ratios, has a long tradition (e.g. Clayton, 1972, 1976;Perry et al, 1973Perry et al, , 1978Goodwin et al, 1976;Baur et al, 1985;Beukes et al, 1990;Kaufman et al, 1990;Mojzsis et al, 1996;Fedo et al, 2006). In recent years, advances in analytical techniques have provided the opportunity to study the stable isotope fractionation of the two major elements in BIFs, Fe and Si.…”

Section: Introductionmentioning

confidence: 99%

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Micro-scale tracing of Fe and Si isotope signatures in banded iron formation using femtosecond laser ablation

Steinhoefel

Horn

Blanckenburg

2009

Geochimica et Cosmochimica Acta

130

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We have detected micrometer-scale differences in Fe and Si stable isotope ratios between coexisting minerals and between layers of banded iron formation (BIF) using an UV femtosecond laser ablation system connected to a MC-ICP-MS. In the magnetite-carbonate-chert BIF from the Archean Old Wanderer Formation in the Shurugwi Greenstone Belt (Zimbabwe), magnetite shows neither intra-nor inter-layer trends giving overall uniform  56 Fe values of ~0.9‰, but exhibits intra-crystal zonation. Bulk iron carbonates are also relatively uniform at near-zero values, however their individual  56 Fe value is highly composition-dependent: both siderite and ankerite and mixtures between both are present, and  56 Fe end member values are 0.4‰ for siderite and -0.7‰ for ankerite. The data suggest either an early diagenetic origin of magnetite and iron carbonates by the reaction of organic matter with ferric oxyhydroxides catalysed by Fe(III)-reducing bacteria; or more likely an abiotic reaction of organic carbon and Fe(III) during low-grade metamorphism. Si isotope composition of the Old Wanderer BIF also shows significant variations with  30 Si values that range between -1.0 and -2.6‰ for bulk layers. These isotope compositions suggest rapid precipitation of the silicate phases from hydrothermal-rich waters. Interestingly, Fe and Si isotope compositions of bulk layers are covariant and are interpreted as largely primary signatures. Moreover, the changes of Fe and Si isotope signatures between bulk layers directly reflect the upwelling dynamics of hydrothermal-rich water which govern the rates of Fe and Si precipitation and therefore also the development of layering. During periods of low hydrothermal activity, precipitation of only small amounts of ferric oxyhydroxide was followed by complete reduction with organic carbon during diagenesis resulting in carbonate-chert layers. During periods of intensive hydrothermal activity, precipitation rates of ferric oxyhydroxide were high, and subsequent diagenesis triggered only partial reduction, forming magnetite-carbonate-chert layers. We are confident that our micro-analytical technique is able to detect both the solute flux history into the sedimentary BIF precursor, and the BIF's diagenetic history from the comparison between coexisting minerals and their predicted fractionation factors.

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Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 74%

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%

“…Further pathways involve the abiotic reduction of Fe(III) (e.g. Perry et al, 1973;Morris, 1993). Alternatively, magnetite incorporates hydrothermal Fe(II) (Ohmoto, 2003).…”

Section: Diagenesis and The Formation Of Magnetite And Iron Carbonatementioning

confidence: 99%