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TitleLake-specific controls on the long-term stability of mining-related, legacy arsenic contamination and geochemical baselines in a changing northern environment, Tundra Mine, Northwest Territories, Canada
AuthorMiller, C B; Parsons, M BORCID logo; Jamieson, H E; Swindles, G T; Nasser, N A; Galloway, J MORCID logo
SourceApplied Geochemistry vol. 109, 104403, 2019 p. 1-18,
Alt SeriesNatural Resources Canada, Contribution Series 20180420
PublisherElsevier BV
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®); html
ProvinceNorthwest Territories
AreaMatthews Lake
Lat/Long WENS-111.2667 -111.0667 64.1000 64.0333
Lat/Long WENS-111.0667 -111.0667 64.1000 64.0333
Subjectssurficial geology/geomorphology; regional geology; environmental geology; geochemistry; geochronology; Nature and Environment; Science and Technology; surface waters; lakes; lake water geochemistry; lake sediment geochemistry; mining; metals; mine waste products; tailings; pollutants; weathering; arsenic geochemistry; climate effects; biogeochemistry; ecosystems; statistical analyses; grain size analyses; lake sediment cores; grab samples; water analyses; radiometric dating; hydroxides; iron geochemistry; sulphides; sulphur geochemistry; flow regimes; flow trajectories; bedrock geology; lithology; igneous rocks; intrusive rocks; diabases; gabbros; quartz porphyries; diorites; volcanic rocks; andesites; basalts; rhyolites; dacites; sedimentary rocks; greywackes; slates; sedimentation rates; pore water samples; textural analyses; Tundra Mine; Salmita Mine; Courageous Lake Greenstone Belt; Canadian Council of the Ministers of the Environment Probable Effects Level; Climate change; environmental baseline studies; cumulative effects
Illustrationslocation maps; geoscientific sketch maps; tables; profiles; photomicrographs; bar graphs; diagrams; schematic representations; pie charts
ProgramEnvironmental Geoscience Metal Mining: northern baselines
Released2019 08 16
AbstractClimate change is influencing the biogeochemistry of northern lake ecosystems. These changes may affect the mobility of naturally occurring metal(loid)s and long-term stability of anthropogenic contaminants. Arsenic (As) concentrations in lake sediments in the Courageous Lake Greenstone Belt, Northwest Territories, Canada, are elevated from the operation of two high-grade, low-tonnage historical gold mines (Tundra Mine and Salmita Mine) and the weathering of mineralized bedrock. In sensitive sub-Arctic environments, it is not currently known how the cumulative effects of resource extraction and climate warming will impact geochemical baselines and the long-term stability of legacy contaminants. In this study, measurements of As concentration and speciation in waters and sediments are combined with multivariate analyses of climate proxies (sediment particle size and organic matter composition) from five lakes downstream of the former Tundra Mine site. Data from lake sediment cores were divided into geochemically distinct populations using a combination of radiometric dating and constrained incremental sum-of-squares cluster analysis to define geochemical baselines, examine the lake-specific controls on As distribution, and determine climate-related factors that may influence the long-term stability of As. Median As concentrations in near-surface impacted sediments (median: 110 mg/kg; range: 31-1,010 mg/kg; n=22) and pre-mining sediment (median: 40 mg/kg; range: 28-170 mg/kg; n=102) exceed the Canadian Council of the Ministers of the Environment Probable Effects Level of 17 mg/kg. Near the Tundra Mine, the long-term stability of As in the near-surface sediment is influenced by the source of As (direct disposal and weathering of waste rock, tailings overtopping and seepage, discharge of treated tailings effluent, weathering and airborne deposition of tailings and waste rock, and natural weathering of mineralized bedrock), lithology of the sediment, and composition of sediment organic matter. This study demonstrates that in lakes impacted by weathering of waste rock and mineralized bedrock, As in sediments is primarily hosted by Fe-(oxy) hydroxides and may be more susceptible to remobilization with climate warming relative to those lakes impacted by direct discharge of mine wastes where As-bearing sulphides are the most abundant As host. Continued climate warming is expected to increase the natural loading of metal(loid)s and organic matter to lake sediments; however, the effects of these changes on the long-term stability of legacy contaminants will vary between lakes.
Summary(Plain Language Summary, not published)
In northern Canada, mining and processing of gold ore has resulted in increased arsenic (As) concentrations in sediments and surface waters up to 30 km from former mine sites. This paper describes results from field and laboratory studies of mine wastes, lake sediments, and surface waters collected from the former Tundra Mine in the Northwest Territories, which was mined for gold in the 1960s and 1980s, abandoned in 1999, then remediated by the Government of Canada from 2007 to 2018. The results of this study show that continued climate warming is expected to increase the natural loading of metal(loid)s and organic carbon to lake sediments in this region. The effects of these changes on the long-term stability of As in lakes depends on the original source of As, the mineral form of As in the sediment, and the composition of organic matter. These results can help guide environmental assessments for future northern metal mines and long-term management decisions for contaminated sites.

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