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TitleSubsurface variations in arsenic mineralogy and geochemistry following long-term weathering of gold mine tailings
AuthorDeSisto, S L; Jamieson, H E; Parsons, M B
SourceApplied Geochemistry vol. 73, 2016 p. 81-97,
Alt SeriesEarth Sciences Sector, Contribution Series 20150407
Mediadigital; on-line
File formatpdf
ProvinceNova Scotia
NTS11F/04; 11D/12
AreaGoldenville district; Montague
Subjectsarsenic; mine waste; mineralogy; gold; remediation; Nova Scotia
Illustrationsgraphs; tables; images
ProgramTools for environmental impacts and adaptation for metal mining, NSERC Natural Sciences and Engineering Research Council of Canada
ProgramEnvironmental Geoscience
AbstractVariations in arsenic (As) mineralogy and geochemical controls on its mobility were evaluated in subsurface tailings at the historical Montague and Goldenville mine sites in Nova Scotia, Canada. Tailings at these sites contain some of the highest As concentrations in Nova Scotia and are located in close proximity to local communities. Pore water in the subsurface tailings is characterized by circumneutral to alkaline pH (6.2 to 8.7) and mildly reducing to oxidizing redox conditions (+130 mV to +347 mV). Bulk chemistry, scanning electron microscopy, and synchrotron micro-X-ray diffraction analyses showed As mineral hosts differ with depth. The deepest tailings (max. 2 m) are in direct contact with partially decomposed vegetation, which supports reducing conditions and the precipitation of authigenic As and Fe sulfides. Under reducing conditions, dissolved As concentrations are also controlled by desorption of As from dissolution of Fe and Mn oxides and the adsorption of As on precipitated carbonates. These geochemical controls differ from those influencing dissolved As concentrations under oxidizing conditions. In the near surface, As mobility is controlled by oxidative dissolution of primary arsenopyrite, precipitation of secondary Fe arsenates, Fe oxyhydroxides and Mn oxides, secondary Ca-Fe arsenates, and sorption onto Fe oxyhydroxides and gangue minerals. The results of this study show that the weathering characteristics of these tailings vary with depth, leading to the formation of new As hosts that are distinct from those observed in the near surface. Identification of these As hosts provides an understanding of current controls on As mobility and has implications for future reprocessing and/or remediation efforts.
Summary(Plain Language Summary, not published)
Mine tailings at historical gold districts in Nova Scotia contain high concentrations of arsenic (As), which may represent a risk to ecosystems and human health. This study focused on two sites, Montague and Goldenville, where tailings are located close to residences and are occasionally used for racing off-road vehicles. This paper describes the results of detailed field and laboratory studies of the tailings carried out by the first author as part of her Ph.D. thesis at Queen's University (completed in May 2014). The study has characterized the main mineral hosts for arsenic in the tailings above and below the water table at these mines, as well as the key processes controlling the release, transport and attenuation of arsenic from the tailings. These results can be used to help guide future remediation activities at historical and modern gold mines in Nova Scotia, and at similar metal mining sites worldwide.