Geochemical characterization of dust from arsenic-bearing tailings, Giant Mine, Canada

Abstract

Dust from uncovered mine tailings at Giant mine, an abandoned mine in northern Canada, has been a concern for nearby residents. We have utilized microanalytical mineralogical analysis combined with quantitative measurements of phase distribution and bulk concentration to fully characterize the dust currently generated from the Giant mine tailings. Surface tailings material was sampled from three tailings impoundments on site and sieved to <63 μm as a proxy for dust, and total suspended particulate (TSP) samples were collected continuously over two months to represent the airborne material that is generated from the tailings. Inductively coupled plasma-optical emission spectrometry (ICP-OES) and -mass spectrometry (ICP-MS) show elevated concentrations of As, Sb, Zn, Pb, Cu and Ni in all samples; comparison of results for sieved and unsieved samples show that As is more concentrated in the <63 μm fraction of the tailings. The X-ray absorption near edge structure (XANES) results for the tailings indicate that the As in the samples is a mixture of As1−, As5+ and As3+. Scanning electron microscope-based mineral liberation analysis (SEM-MLA) results show that roaster-generated iron-oxides (i.e., maghemite), calcium-iron arsenate (i.e., yukonite), and arsenopyrite comprise the majority of the As-bearing particles in the surface tailings; of these three solid phases, calcium-iron arsenate poses the greatest risk to human health as it exhibits the highest relative bioaccessibility. A rare lead arsenate phase, which may be bioaccessible, was also detected in minor quantities in the surface tailings; this phase was identified as mimetite through μXRD analysis. Very little arsenic trioxide was found in the surface tailings samples, and no arsenic trioxide was found in the TSP samples; this is because the tailings that were exposed to arsenic trioxide-bearing roaster stack emissions during the 1950s and 1960s have been buried by more recent tailings. Soils near the Giant mine tailings have been found to contain arsenic trioxide from historic stack emissions, which indicates that the mine-impacted environmental media surrounding a tailings impoundment could in some cases pose a greater risk to environmental and human health than the tailings themselves.