Arsenic (As) contamination presents an ecosystem and human health risk at Giant Mine, a historic gold mine near Yellowknife, NWT currently undergoing the final stages of assessment for remediation. Arsenic concentration is elevated in sediments at Giant Mine due to contamination from several forms of mine waste including flotation tailings, roaster calcine and impoundment spills. The Giant Mine Remediation Project has stated aims to remediate the surface of the site, including Baker Creek which runs through the property, to a condition that is a productive environmental habitat and spawning ground. Environmental scanning electron microscope (ESEM) and synchrotron-based micro- X-ray Absorption Near Edge Spectroscopy (µXANES), micro-X-ray fluorescence (μXRF) and micro-X-ray diffraction (μXRD) techniques were employed to characterize the As-host phases and determine the solid-phase speciation of As in mine waste and sediments. Arsenopyrite, Fe-oxides, Fe-root plaque, and As_2 O_3 were the major phases identified. Sediment toxicity was measured using 10-day Chironomus dilutes and 21-day Pimephales promelas exposure tests. The toxicity tests found responses ranging of from 100% mortality at the most contaminated site to no statistical difference to the control groups in the least As contaminated site. Toxicity test chamber conditions were directly monitored with dialysis probes (mini-peepers) and Diffusive Gradients in Thin Films (DGTs). DGT and mini-peeper deployment in the test beakers allowed for direct correlation of their measurements to trace metal uptake and bioaccumulation during the toxicity tests. Linear regression and ANOVA statistics were used to correlate, when possible, As tissue concentrations in Chironomus dilutes and Pimephales promelas to DGT, mini-peeper and surface water concentration measurements. Statistical analysis was also conducted for Co, Cr, Cu, Ni, Pb, Zn, and Sb though these other metal/metalloids were not always suitable for analysis due to constraints caused by detection limits. It was found that DGT As was statistically correlated (r2=0.836 and p<0.0005) to uptake in Pimephales promelas but that total element concentrations were also statistically relevant and slightly better at predicting uptake (r2=0.873 and p<0.0005). Mini-peepers could not be analyzed statistically due to challenges in their use within some highly vegetated sediment samples. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2014-05-01 11:47:59.482

Anthropogenic and geogenic sources of arsenic (As) have been identified in mining-impacted soils from the Giant mine (1948-1999), NT and the North Brookfield mine (1886-1906), NS. Both used roasting to extract gold from the arsenopyrite ore, decomposing it to As-bearing iron oxides (roaster oxides or RO) containing As, and releasing As3+-bearing arsenic trioxide (As2O3). Arsenic trioxide is considered highly soluble with the dissolved As3+ species being more mobile and toxic than other oxidation states. Soil profiles from the Giant mine show elevated As and antimony (Sb) at the surface (As=140-3300ppm) and decreasing concentrations with depth (As=22-600ppm). Surface soils contain anthropogenically-derived As2O3 identified using synchrotron methods (µXRD, µXANES) and environmental SEM. The persistence of As2O3 is attributed to Sb in As2O3 grains, dry climate and high organics in the soils. Anthropogenically-derived RO of maghemite (containing both As3+ and As5+) and natural arsenopyrite were observed. Sequential selective extractions (SSE) from surface soils show between 20% and 75% of As extracted in the crystalline iron-oxide phase is attributed to As2O3 and RO, while at depth As is bound by organics in the weaker leaches. North Brookfield mine soils show lower total As (2ppm to 45ppm) except near the roaster (4300ppm). No As2O3 was identified, probably due to the smaller scale and age of the mine, lower organic content and the lack of Sb. As-bearing phases include RO of hematite (As5+), As-rich rims on titanium-oxides, and As associated with clays and goethite. Adjacent to the roaster, SSE show As was also in the amorphous iron-oxide phase, also shown by As in arsenopyrite weathering rims. There are many differences between the North Brookfield and Giant mine soils including roasting techniques which produced different RO mineralogy, the scale of mining, climate, soil type, and the presence of As2O3. Currently, the Giant property is not publically accessible but may become so in the future while the North Brookfield property is accessible. Understanding the form and distribution of As phases is critical because of the potential risk to human and ecosystem health associated with ingestion of soil particles and their control on the total dissolved As in surface and groundwater. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2008-09-29 17:21:50.73

In the last 150 years, the City of Yellowknife has transitioned from an area of traditional subsistence living to the largest city in the Northwest Territories (Canada) due to the economic influence of resource extraction. As resource extraction in the area boomed, large quantities of pollutants from mine tailings and emissions from roaster stacks adjacent to gold mines were deposited on the landscape, leaving a known legacy of elevated surface water, sediment, and soil metal(loid) concentrations. Most of the research to date has focused on arsenic in the region, and my thesis expands the body of knowledge to include other metal(loids) of interest, including antimony, lead, and mercury. My thesis's main objective was to determine the spatial and temporal extent of legacy mining emissions near Yellowknife and assess the associated biological risk from these historic emissions. I analyzed select intervals from 20 lake sediment cores for time constrained metal(loid) contaminants of concern. I used a combination of paleotoxicity and paleoecotoxicology methods to establish a spatial and temporal footprint of biological risk associated with historic gold mining activities in the Yellowknife region. I determined that lakes close to the mine exhibited a low-level hazard to aquatic communities before mining, while the onset of mining increased the hazard posed by sediments deposited to acute levels. I also discovered that lakes within 5 km of Giant Mine exceeded guideline values for sedimentary mercury during active mining. Further, I developed methods in paleoecotoxicology that indicated a concordance between time deposited, estimated risk, and observed mortality of native Daphnia sp exposed to time-constrained sediment archives. My thesis demonstrates that paleotoxicity and paleoecotoxicology are effective methods to separate historic and modern influences of industrial development on aquatic biota. Additionally, my research has application extensions for policymakers, remediation scientists, Indigenous Peoples, and those proposing new industrial ventures.