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Limited Zn and Ni mobility during simulated iron formation diagenesis

DOI: 10.1016/j.chemgeo.2015.02.037 DOI Help

Authors: Leslie J. Robbins (Department of Earth and Atmospheric Sciences, University of Alberta) , Elizabeth D. Swanner (Center for Applied Geosciences, University of Tübingen) , Stefan Lalonde (European Institute for Marine Studies) , Merle Eickhoff (Center for Applied Geosciences, University of Tübingen) , Megan L. Paranich (Department of Earth and Atmospheric Sciences, University of Alberta) , Curistopher T Reinhard (School of Earth and Atmospheric Sciences, Georgia Institute of Technology) , Caroline Peacock (School of Earth and Environment, University of Leeds) , Andreas Kappler (Geomicrobiology Group, Center for Applied Geosciences, University of Tübingen) , Kurt Konhauser (rtment of Earth and Atmospheric Sciences, University of Alberta)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Chemical Geology , VOL 402 , PAGES 30 - 39

State: Published (Approved)
Published: May 2015
Diamond Proposal Number(s): 8624

Abstract: Iron formations (IF) are iron- and silica-rich chemical precipitates that were deposited during the Precambrian. Several recent studies have demonstrated how the trace metal abundances in IF can be used as proxies for the bioavailability of trace metals in ancient seawater; with the ultimate goal being to understand first-order controls on the composition of the ancient biosphere. However, the utility of IF as proxies depends on the immobilization of trace metals during diagenesis. Here, we assess the mobility of Zn and Ni from ferric oxyhydroxides (ferrihydrite) in the absence and presence of organic matter (glucose) during simulated diagenesis (170 °C, 1.2 kbar); similar to what some Precambrian IF experienced. Quantitative concentration data, coupled with X-ray diffraction analysis and electron microprobe element mapping, demonstrate that both metals are relatively immobile during simulated diagenesis. Additionally, the mechanism for initial Ni sorption is examined using X-ray adsorption spectroscopy. For the initial sorption of trace elements in abiotic ferrihydrite experiments, 93.38% Zn and 65.95% Ni were initially sorbed. In experiments utilizing biogenic ferrihydrite, 97.03% of Zn and 93.38% of Ni were initially sorbed. Following the diagenetic capsule treatments, more than 99% of Zn and more than 91.9% of Ni were retained under the varied conditions considered here. Capsule experiments suggest the strong retention of Zn and Ni following the diagenesis of either abiotic or biogenic ferrihydrite. Overall, our results indicate that paleomarine Zn and Ni concentrations are likely to be faithfully recorded in well-preserved IF deposits.

Journal Keywords: Iron Formations; Zinc; Nickel; Diagenesis; Iron Oxyhydroxides; Trace Metal Mobility

Subject Areas: Chemistry, Earth Science, Materials

Instruments: B18-Core EXAFS

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