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Using Zn and Ni behavior during magnetite precipitation in banded iron formations to determine its biological or abiotic origin

Abstract : There is longstanding controversy about the genesis of magnetite in banded iron formations (BIFs), particularly concerning whether it is of abiogenic or biogenic origin. The composition of trace elements within magnetite produced by magnetotactic bacteria has been proposed as a promising marker for its biological origin; however further experimental evidence is required to investigate whether this also holds true for iron-metabolizing bacteria. Here, we compared the behavior of zinc (Zn) and nickel (Ni) in magnetite produced either abiogenically (ferrihydrite reacting with dissolved Fe2+) or biogenically (ferrihydrite reacting with dissolved Fe2+ generated via the dissimilatory iron-reducing bacterium - DIRB - Shewanella oneidensis MR-1). These abiotic and biotic incubations were applied for transforming three ferrihydrite (Fh) substrates: (1) Control Fh without added trace elements; (2) Zn-coprecipitated ferrihydrite (ZnFh); and (3) Ni-coprecipitated ferrihydrite (NiFh) in both NaHCO3 and HEPES buffer. X-ray diffraction revealed magnetite as the dominant transformation product for all reaction conditions, while siderite was only detected in experiments containing NaHCO3 as buffer. Based on similar initial dissolved Ni and Zn concentrations, we found opposing behavior of Zn and Ni where Zn showed enrichment in abiogenic magnetite, while Ni was more enriched in biogenic magnetite. Combining supposed Zn and Ni concentrations in Precambrian seawater and magnetite mineral grains from three formations deposited at different ages (i.e. 3.75 Ga Nuvvuagittuq Supracrustal Belt, 2.45 Ga Weeli Wolli Iron Formation, and 1.88 Ga Sokoman Iron Formation), we reconstructed potential Zn and Ni partition coefficients between Precambrian seawater and magnetite minerals. The reconstructed potential Zn and Ni partition coefficients suggested that these magnetite minerals from three formations were abiogenic. These differing behaviors suggest the possibility of using Zn and Ni partition coefficient ratios as a means of determining the presence or absence of DIRB in the formation of ancient magnetite deposits.
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Submitted on : Monday, March 21, 2022 - 11:35:54 AM
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Xiaohua Han, Elizabeth Tomaszewski, Ronny Schoenberg, Kurt Konhauser, Matthieu Amor, et al.. Using Zn and Ni behavior during magnetite precipitation in banded iron formations to determine its biological or abiotic origin. Earth and Planetary Science Letters, Elsevier, 2021, 568, pp.117052. ⟨10.1016/j.epsl.2021.117052⟩. ⟨cea-03615009⟩



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