ENVIRONMENTAL RISK POTENTIAL OF TELLURIUM-RICH MINE TAILINGS IN A HISTORIC MINING DISTRICT IN DELAMAR, NEVADA

Mine tailings often host elevated concentrations of toxic metal(loid)s that represent a health risk to the environment. The historic Delamar Mining District, active from 1891 to 1938, is located in semi-arid Lincoln County, NV. Today, at least 450,000 tons of tailings remain at the site that contain elevated concentrations of tellurium (Te; up to 455 mg kg^-1) and other toxic metal(loid)s (e.g., As, Cu, Pb, and Zn up to 46, 308, 402, and 201 mg kg^-1, respectively) . These elements have the potential to have deleterious impacts on surrounding ecosystems and communities through the dispersion of their particles by wind and surface water transport. Therefore, our goal is to determine whether metal(loid)s in these Te-rich historic mine tailings weather to more mobile and bioaccessible forms, posing a health risk to surrounding ecosystems and communities.

In this study, two distinct tailings piles were sampled as a function of depth. Extensive mineral weathering, indicated by sulfur X-ray absorption spectroscopy (XAS), influences metal(loid) speciation, which controls mobility and bioaccessibility. Tellurium and other toxic metal(loid)s, such as Cu and Pb, are enriched at the tailings surface, potentially as efflorescent salts or sorbed species. Physiologically-based extraction tests (PBETs) of surficial tailings with stomach fluids for Te, As, Cu, Pb, and Zn reveal bioaccessibility up to 10, 4, 19, 17, and 46%, respectively, indicating that these materials may be toxic if ingested. Aeolian transport, a dominant dispersion mechanism in semi-arid climates, has been demonstrated to disperse metal(loid)s at this site through sampling of surficial soils near the mill and tailings piles. Roughly 50% of tailings particles are wind transportable with diameters less than 37 µm and, if inhaled, PBETs indicate that 1, 7, 25, 0.01, and 0.3% of Te, As, Cu, Pb, and Zn, respectively, are bioaccessible. Tellurium bulk XAS indicate the predominance of Te(VI), which is less soluble and toxic than Te(IV), likely responsible for the low percentages of bioaccessible Te in the tailings. Taken together, these results lend insight into the potential health and environmental impacts of Te-rich mine tailings.