TY - JOUR
T1 - Biogeochemical cycling of silver in acidic, weathering environments
AU - Shuster, Jeremiah
AU - Reith, Frank
AU - Izawa, Matthew R.M.
AU - Flemming, Roberta L.
AU - Banerjee, Neil R.
AU - Southam, Gordon
N1 - Funding Information:
Acknowledgments: Special thanks to R. Hodder, N. Badham, F. Barriga, J. Relvas, C. Rosa, J. Matos, S. Porter, S. Clemmer and R. Moore for mentorship during the International Geoscience Field Experience of the Iberian Pyrite Belt 2009. Travel support for J.S. was provided by International Curriculum Fund and the Bob Hodder Travel Fund, Western University. Funding for R.L.F., N.R.B. and G.S. was provided by Natural Science and Engineering Research Council of Canada Discovery Grants. Funding for G.S. was provided by the Australian Research Council (ARC) Discovery Program (DP130102716). Funding for F.R. was provided by ARC Future Fellowship grant (FT150100250). Geochemical analysis was performed at the Laboratory for X-ray Diffraction and Micro-Diffraction and the Geoanalysis Laboratory at Western University, Canada. Electron microscopy and microanalysis was performed at the: Biotron Integrated Imaging Facility (Western University), Centre for Microscopy and Microanalysis (University of Queensland, Australia) and Adelaide Microscopy (University of Adelaide, Australia).
Publisher Copyright:
© 2017 by the authors. Licensee MDPI, Basel, Switzerland.
PY - 2017/11
Y1 - 2017/11
N2 - Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples were analyzed for Ag mineralogy, content, and distribution using micro-analytical techniques and high-resolution electron microscopy. While Ag concentrations were variable within these materials, elevated Ag concentrations occurred in gossans. The detection of Ag within younger regolith materials, i.e., terrace iron formations and mine soils, indicated that Ag cycling was a continuous process. Microbial microfossils were observed within crevices of gossan and their presence highlights the preservation of mineralized cells and the potential for biogeochemical processes contributing to metal mobility in the rock record. An acidophilic, iron-oxidizing microbial consortium was enriched from terrace iron formations. When the microbial consortium was exposed to dissolved Ag, more than 90% of Ag precipitated out of solution as argentojarosite. In terms of biogeochemical Ag cycling, this demonstrates that Ag re-precipitation processes may occur rapidly in comparison to Ag dissolution processes. The kinetics of Ag mobility was estimated for each type of regolith material. Gossans represented 0.6–146.7 years of biogeochemical Ag cycling while terrace iron formation and mine soils represented 1.9–42.7 years and 0.7–1.6 years of Ag biogeochemical cycling, respectively. Biogeochemical processes were interpreted from the chemical and structural characterization of regolith material and demonstrated that Ag can be highly dispersed throughout an acidic, weathering environment.
AB - Under acidic, weathering conditions, silver (Ag) is considered to be highly mobile and can be dispersed within near-surface environments. In this study, a range of regolith materials were sampled from three abandoned open pit mines located in the Iberian Pyrite Belt, Spain. Samples were analyzed for Ag mineralogy, content, and distribution using micro-analytical techniques and high-resolution electron microscopy. While Ag concentrations were variable within these materials, elevated Ag concentrations occurred in gossans. The detection of Ag within younger regolith materials, i.e., terrace iron formations and mine soils, indicated that Ag cycling was a continuous process. Microbial microfossils were observed within crevices of gossan and their presence highlights the preservation of mineralized cells and the potential for biogeochemical processes contributing to metal mobility in the rock record. An acidophilic, iron-oxidizing microbial consortium was enriched from terrace iron formations. When the microbial consortium was exposed to dissolved Ag, more than 90% of Ag precipitated out of solution as argentojarosite. In terms of biogeochemical Ag cycling, this demonstrates that Ag re-precipitation processes may occur rapidly in comparison to Ag dissolution processes. The kinetics of Ag mobility was estimated for each type of regolith material. Gossans represented 0.6–146.7 years of biogeochemical Ag cycling while terrace iron formation and mine soils represented 1.9–42.7 years and 0.7–1.6 years of Ag biogeochemical cycling, respectively. Biogeochemical processes were interpreted from the chemical and structural characterization of regolith material and demonstrated that Ag can be highly dispersed throughout an acidic, weathering environment.
KW - Argentojarosite
KW - Gossan
KW - Iron-oxidizing bacteria/archaea
KW - Silver biogeochemical cycling
KW - Terrace iron formations
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U2 - 10.3390/min7110218
DO - 10.3390/min7110218
M3 - Article
AN - SCOPUS:85034033955
VL - 7
JO - Minerals
JF - Minerals
SN - 2075-163X
IS - 11
M1 - 218
ER -