|Titre||Controls on uranium, rare earth element, and radionuclide mobility at the decommissioned Bicroft Uranium Mine, Ontario|
|Auteur||Parsons, M B; Friske, P W B; Laidlow, A M; Jamieson, H E|
|Source||Atlantic Geoscience Society 40th Colloquium and Annual Meeting, program with abstracts; 2014 p. 36|
|Liens||Online - En ligne |
|Éditeur||Société géoscientifique de l'Atlantique|
|Réunion||Atlantic Geoscience Society 40th Colloquium and Annual Meeting; Wolfville; CA; février 7-9, 2014|
|Media||numérique; en ligne|
|Référence reliée||Cette publication est reliée Parsons, M B;
Friske, P W B; Laidlow, A M; Jamieson, H E; (2014). Controls on uranium, rare earth element, and radionuclide mobility at the decommissioned Bicroft Uranium Mine, Ontario, Commission géologique du Canada, Présentation scientifique no.
|Lat/Long OENS||-78.0500 -78.0333 45.0000 44.9833|
|Sujets||uranium; gisements d'uranium; radionucléïdes; résidus; analyses des résidus; géochimie des résidus; radioactivité; déchet radioactif; eaux de surface; géochimie des sediments lacustres; géochimie des eaux
lacustres; sediments lacustres; eaux lacustres; fer; hydroxydes; thorium; géologie économique; géochimie; minéraux métalliques; géologie de l'environnement|
|Illustrations||location maps; photographs; plots; graphs|
|Programme||Outils d'adaptation et d'impacts sur l'environnement pour les mines de métaux, Géosciences de l'environnement|
|Résumé||(disponible en anglais seulement)|
Uranium ores have been mined in Canada since the 1930s, resulting in the production of approximately 214 million tonnes of mill tailings. These tailings may
pose a risk to ecosystems and human health because of their long- lived radioactivity, and their potential to release radionuclides, metal(loid)s, radon gas, and milling reagents to the environment. The main objective of this study was to
characterize the processes controlling the release, transport, and fate of U, radionuclides ( 226 Ra, 210 Pb), and rare earth elements (REEs) downstream from two decommissioned tailings impoundments at the Bicroft Uranium Mine near Bancroft, Ontario.
The Bicroft Mine operated from 1957 to 1963, and milled approximately 2,470,000 tonnes of U ore from granitic pegmatite dykes. This type of U deposit is relatively widespread throughout the Grenville Province in Ontario, Québec, and Labrador, and has
recently been the focus of exploration as a source of REEs and other strategic metals. Samples of tailings, sediments, surface waters, and colloids were collected from the Bicroft Mine between 2010 and 2012. Regional-scale sampling of sediments and
waters, as well as reanalysis of archived stream and lake sediments, were undertaken to determine natural background variation. The concentration of U in the Bicroft tailings samples varies from 3.1 to 210 mg/kg (median 19 mg/kg). Much higher
concentrations were found in stream and pond sediments below the tailings impoundments (54 to 730 mg/kg; median 150 mg/kg). Uranium concentrations in regional lake sediments range from 0.4 to 140 mg/kg (median 4.2 mg/kg), and regional stream
sediments range from 1.2 to 110 mg/kg (median 4.6 mg/kg). Seasonal sampling of tailings effluent shows that these waters are circumneutral (pH 6.6-8.3) and that the downstream concentrations of U and 226 Ra are generally highest in the fall.
Comparison of filtered and unfiltered effluents, combined with synchrotron microanalyses of colloids, shows that the downstream mobility of REEs is limited by sorption to Fe- and Mn-oxyhydroxides. In contrast, U occurs mainly in the dissolved phase
and its mobility does not appear to be limited by sorption to colloids or precipitation of secondary U phases. Geochemical modeling of the effluent demonstrates that the aqueous speciation of U is dominated by calcium-uranyl-carbonato complexes [e.g.
Ca 2 UO 2 (CO 3 ) 3 ], which are known to diminish the sorption of U to mineral surfaces and suppress the reduction of U(VI) to less soluble U(IV). The results of this study provide improved understanding of the long-term stability of U tailings, and
have implications for the design of environmental monitoring plans.