CHARACTERIZATION OF ARSENIC-HOSTING SOLID PHASES IN TAILINGS AND TAILINGS DUST FROM GIANT MINE, YELLOWKNIFE, NT

Mining and ore processing at Giant Mine, a gold mine in northern Canada, occurred for over 50 years (1948 – 1999). Roasting the arsenopyrite-bearing gold ore generated As-bearing maghemite, As-bearing hematite, and arsenic trioxide (As₂O₃) which were co-deposited with flotation tailings. Arsenic trioxide is considered the most bioaccessible arsenic compound. After spring thaw in May the temperature is too low to apply any chemical surfactant to the Giant Mine tailings, thus there is a window of time when the tailings are exposed to surface conditions. This window coincides with north-northwesterly high velocity wind events (> 8.0 m/s) in May and June. There has been growing concern regarding the potential arsenic concentration and arsenic speciation of the dust from Giant Mine. The objective of this research is to characterize the mineralogy of the fine fraction of the tailings (particles <20μm in diameter) to determine what arsenic-hosting solid phases are present, and to identify the arsenic-hosting species. Eighteen samples of surface tailings (0-10cm) were taken from locations within the tailings ponds where dust generation has been observed in the past. These samples have been sieved to <100μm to isolate the finest fraction for analysis. From May to July a Met One E-Sampler and a total suspended particulate (TSP) high volume air sampler were set up at the south end of the south-most tailings pond to collect samples of the airborne material that was transported from the mine property to N’Dilo – a community of Yellowknives Dene First Nations (YKDFN) located directly south of Giant Mine. A 47mm Teflon filter was collected from the E-sampler every 7 days, and a quartz filter was collected from the TSP high volume sampler every 3 days. For all of the surface tailings and dust samples we are using inductively coupled plasma mass spectrometry (ICP-MS) to determine the total concentration of arsenic in the samples, coupled with scanning electron microscopy-mineral liberation analysis (SEM-MLA) and synchrontron-based micro X-ray diffraction (μXRD), mirco X-ray fluorescence (μXRF), and X-ray absorption near edge structure (XANES) work to speciate the arsenic in the surface tailings and tailings dust. By these methods we are compiling data that may be used in an assessment of the relative risk posed by the Giant Mine tailings dust.