TELLURIUM SPECIATION AND DISTRIBUTION AS A FUNCTION OF DEPTH IN SEMI-ARID MINE TAILINGS

Historic mine tailings frequently host elevated concentrations of toxic metals that represent a health risk to surrounding ecosystems and communities. In semi-arid environments, the surficial accumulation of toxic metals in bioaccessible efflorescent salts generates metal-laden particles vulnerable to aeolian transport over regional scales. The goal of this project is to examine the geochemical weathering of Te in a semi-arid environment in order to: 1) assess Te bioaccessibility and mobility with respect to assessing human health risk, and 2) assess the potential for reprocessing of historic Te-rich mine tailings as future Te-resources.

To that end, we sampled two piles of circum-neutral (pH 7.3-8.3) tailings with depth at the historic Delamar mill (Lincoln County, NV) mined from 1891-1938. Delamar is a semi-arid site, with average precipitation of 251 mm and evapotranspiration potential of 380 mm, and sparse to no vegetative cover of the tailings. Surficial tailings contain elevated concentrations of tellurium (Te; up to 267 mg kg^-1) and other metals (e.g., Pb, Bi, Cu, and As), pointing to the formation of efflorescent salts that are both bioaccessible and vulnerable to erosive dispersion. Tellurium and S speciation were examined using X-ray absorption spectroscopy (XAS) and spatial elemental relationships explored with X-ray fluorescence (XRF). Both sulfate and sulfide phases were present in the tailings at multiple depths, but only Te(VI), the less toxic form of Te, was detected. XRF also reveals a strong spatial collocation of Te and S in surficial tailings that does not exist at depth. These preliminary results lend insight into Te weathering in a semi-arid environment.