Crustal Imaging and Characterization Team

Using stable isotopes of S and transition metals as tracers of processes in mining impacted environments

Subtask Objectives

The objectives of this task are to define the distribution of stable metal (e.g., Cu, Fe, Hg, Mo, and Zn) isotopes in mining impacted environments, to understand how abiotic and biotic processes, including redox, adsorption, and precipitation, define the isotopic signatures of samples from the field and well-controlled laboratory experiments, and to use that understanding to advance our knowledge and modeling of how elements cycle through the environment.

Statement of Work

Both field and laboratory studies are planned. Because there is virtually no published information about isotopic distributions of dissolved stable metals (Cu, Hg, Mo, and Zn) in the environment, we will begin with a survey of the isotopic signatures of dissolved and particulate samples from selected mining environments, with an emphasis on sites containing significant deposits of chalcopyrite, sphalerite, and cinnabar. Our approach is to use a combination of archived and previously characterized mine drainage samples and to collect new field samples that contain variable concentrations of Cu, Hg, and Zn.

Second, previously published work indicates fractionation of Fe and Mo during adsorption onto Fe and Mn oxides, respectively (Barling and Anbar, 2002; Icopini et al., 2004) . A series of controlled laboratory experiments are planned to determine whether there is fractionation during adsorption of Cu, Mo, and Zn onto Fe oxides, and to provide information about the relative importance of adsorption in determining isotopic signatures of Cu and Zn in the environment. If there is fractionation during adsorption, then experiments will be done to assess how solution composition (i.e., element speciation) affects fractionation during adsorption. The experiments will complement isotopic work that is currently being done on samples from a mixing and reaction zone downstream of the confluence of a pristine river with acid-rock drainage in Vermont and from a study of groundwater-surface water interactions in the mining impacted Redwell Basin.

Barling, J., and Anbar, A.D., 2002, Mo scavenging by manganese oxyhydroxides and the seawater Mo isotope record in oxic sediments:Geochimica et Cosmochimica Acta 66, A52.

Icopini, G.A., Anbar, A.D., Ruebush, S.S., Tien, M., and Brantley, S.L., 2004, Iron isotope fractionation during microbial reduction of iron: The importance of adsorption: Geology 32, 205-208.

Highlights & Key Findings

Wanty, et al. (2005) have developed a novel new technique for separation and analysis of Cu, Fe, and Zn from water samples and these results were presented at the 2005 Annual GSA meeting.

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