M.J. Palmer – Carleton University, Ottawa, ON; Aurora Research Institute, Aurora College, Yellowknife, NT, Canada
A sediment sampling program was conducted in Yellowknife Bay with the objective of characterizing arsenic (As) and antimony (Sb) mineralogy, enriched in sediment from former regional gold mining operations. Nine sediment cores were collected over three field seasons. Sediment cores were extruded under nitrogen atmosphere and subsamples at 0.5 cm and 1 cm intervals were analyzed for bulk elemental concentration by ICP-MS and automated mineralogy by SEM-MLA. Measurements within the sediment profile indicated that As is mobile both downwards, where it precipitates as authigenic sulfides, and upwards where it is attenuated by Fe-oxyhydroxides and potentially roaster-generated Fe-oxides near the sediment-water interface. Antimony appears to be stable in Yellowknife Bay sediments, and no evidence of post-depositional mobility was identified. The prevalence of arsenic trioxide in modern day near-surface sediments proximal to a former gold mine suggests that As and Sb contamination, likely from terrestrial weathering of contaminated soils on site, is ongoing. No seasonal difference in mineralogy was detected in a mid-bay offshore sampling site. However, the widespread occurrence of As- and Sb-bearing oxide minerals in near-surface sediments may affect water quality should sediment oxygen conditions deteriorate in the future, which would destabilize As-bearing oxide mineral hosts.