Analysis of lake sediments and peat cores

Peats and lake sediments are natural archives of past environmental conditions. Detailed identification and characterization of the arsenic (As)-hosting minerals preserved in these archives can be used to understand and predict the transport and fate of As in terrestrial and aquatic systems. The deliverables of this request will help Natural Resources Canada (NRCan) to better understand how As is hosted in near-surface solid phase materials in northern ecosystems of the Yellowknife region, where approximately seventy-five years of gold mining and associated contamination obscures geochemical background. Peats and lake sediments have been collected from the Yellowknife region, Northwest Territories, and they will be sub-sampled for various analyses, including mineralogy. By studying the mineralogy of As, NRCan will be able to determine if solid phase As is geogenic or anthropogenic in origin, and thus characterize the environmental impact of past mining activity. Previous work has shown that the application of synchrotron-based techniques, scanning electron microscopy, and Mineral Liberation Analysis can be successfully used to distinguish As compounds known to have been emitted from historical stack emissions at Giant Mine, including arsenic trioxide and As-hosting maghemite and hematite, from arsenopyrite and other forms that are more likely to be natural in origin. Detailed micromineralogical analyses have also shown how post-depositional diagenesis can convert arsenic trioxide in lake sediments to less bioaccessible arsenic-bearing sulfide minerals.