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Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides
Published on: May 20, 2019
Iron isotope fractionation by biogeochemical processes in mine tailings
Roger B Herbert1, Axel Schippers
1Department of Earth Sciences, Uppsala University, Villavädgen 16, 75236 Uppsala, Sweden. roger.herbert@geo.uu.se
Abstract:
Iron isotope ratios were determined for the pore water, the 1 M HCl/1 M hydroxylamine hydrochloride (HAH)-extractable solid phase, and the total extractable solid phase from sulfidic mine tailings in Impoundment 1, Kristineberg mine, northern Sweden. Within the tailings, pyrite oxidation occurs in a distinct Fe-depleted oxidation zone, and the greatest number of Fe(II)-oxidizing bacteria in the profile occur close to the boundary between oxidized and unoxidized tailings. Above the oxidation front in the oxidized tailings, a large iron isotope fractionation (-1.3 to -2.4% per hundred) is measured between the pore water and the HAH-extractable solid phase. This isotope fractionation is explained by aqueous Fe(II)-Fe(III) equilibrium, microbial Fe(II) oxidation, and Fe(III) oxyhydroxide precipitation. The data suggests that pyrite in the tailings is enriched in 56Fe relative to Fe-rich silicates in the same material, such that pyrite oxidation results in a decrease in the mean delta56Fe value for the bulk tailings in the oxidized zone: a change in isotope composition that is not attributable to isotope fractionation. Iron isotope analyses yield valuable information on iron cycling in mine wastes, and they have the potential for becoming a tool for the prediction and control of acid mine drainage.
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