AN ASSESSMENT OF TELLURIUM IN SEMI-ARID MINE TAILINGS AT DELAMAR, NEVADA: IMPLICATIONS FOR HUMAN AND ECOSYSTEM HEALTH

The global processing of precious metal ores has resulted in legacy, unreclaimed mine wastes that can release substantial amounts of hazardous elements to the environment. The historic Delamar mining district, located in semi-arid Lincoln County, NV, was mined for Au from 1891 to 1938 and produced at least 450,000 tons of mine tailings containing elevated concentrations of tellurium (Te; up to 267 mg kg^-1). Tellurium, since it demonstrates properties similar to As and Se, is considered to be toxic to humans, Te^IV more than Te^VI. Although Te is sometimes enriched in Au/Ag deposits, it isn’t recovered, resulting in the environmental release of significant amounts of Te. The weathering of Te-bearing mine tailings in surficial environments can transform Te and have implications for human and environmental health.

Our goal is to examine the geochemical weathering of Te at Delamar in order to assess Te bioaccessibility and mobility. Two circum-neutral (pH 7.4-8.3) tailings piles with strikingly different physicochemical characteristics were sampled as a function of depth. Tellurium and other toxic metal(loid)s (e.g. Pb, Bi, Cu, and As) are enriched in surficial tailings, likely present as bioaccessible efflorescent salts, and may be susceptible to dispersion by wind or surface water erosion. Bulk fits modeling Te speciation via X-ray absorption spectroscopy (XAS) suggest the predominance of Te^VI, the less toxic form of Te. Micro-focused X-ray fluorescence (µ-XRF) mapping and electron microscopy indicate the enrichment of Te in small (2-3 µm) particles and a strong spatial correlation between Te and S, and sometimes with Au. HYSPLIT modeling suggests the dominant wind direction is to the northeast, but winds can blow toward Las Vegas, a nearby population center. Roughly 50% of particles by weight have diameters below the wind transportable threshold of ~35 µm, indicating these tailings may be dispersed to population centers. Taken together, these results lend insight into the effects of Te weathering on the potential health and environmental impacts of Te.