Interpretation of Zn Isotope Ratio Measurements in a Complex Geochemical System

Blowes, D.W., Lindsay, M.J.B., Matthies, R., Veeramani, H., Kong, L., Eagling, J. and Ptacek, C.J. (2015) Interpretation of Zn Isotope Ratio Measurements in a Complex Geochemical System. In: Goldschmidt 2015, Prague, Czech Republic, 16-21 Aug 2015,

Abstract

Zinc isotope ratios were measured for pore water samples collected from a pilot-scale remediation system designed to asssess the potential benefits of promoting bacterial SO4 reduction and precipitation of metal sulfides. Samples were collected from three test cells at the Greens Creek mine (Alaska, USA), including a control cell and two treatment cells. Cells TC4 and TC7 were amended with organic carbon. The first treatment cell (TC4) contained 5 vol.% organic carbon as peat (2.5 vol. %) and spent brewing grain (2.5 vol. %), and the second treatment cell (TC7) contained 10 vol.% organic carbon as peat (5 Vol. %), spent brewing grain (2.5 vol. %) and municipal biosolids (2.5 vol. %). High concentrations of dissolved Zn (97 to 320 mg L-1 ) and SO4 near the tailings surface indicate Zn release by sphalerite [(Zn,Fe)S] oxidation. Zinc isotope ratios near the tailings surface in all three cells were similar and ranged between +0.25 and +0.35 ‰ (δ66Znavg = +0.3 ±0.05 ‰). At depths equal or below 1 m below surface, Zn concentrations were generally below 2.7 mg L-1 in TC4 and TC7 and below 7.1 mg L-1 in TC2. This decline in Zn concentrations in TC4 and TC7 is attributed bacterial SO4 reduction and concomitant alkalinity production, leading to extensive precipitation of Zn sulfide phases and potentially Zn carbonate phases. Zinc isotope measurements indicate Δ66Zn values of up to -0.35 ‰. Laboratory studies indicate precipitation of Zn sulfide phases results in preferential incorporation of 64Zn, resulting in increasingly positive δ 66Zn values, whereas precipitation of Zn carbonate leads to increasingly negative δ66Zn values. These observations suggest that precipitation of a combination of secondary sulfide and carbonate phases controls Zn mobility and isotope ratios under SO4-reducing conditions within the amended cells.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Veeramani, Dr Harish
• Authors: Blowes, D.W., Lindsay, M.J.B., Matthies, R., Veeramani, H., Kong, L., Eagling, J., and Ptacek, C.J.
• College/School: College of Science and Engineering > School of Engineering > Infrastructure and Environment

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