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TitleTransport and fate of uranium, rare earth elements, and radionuclides from decommissioned tailings at the historical Bicroft Uranium Mine, Ontario
AuthorParsons, M B; Friske, P W G; Ford, K L; LeBlanc, K W G
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Programs with Abstracts vol. 36, 2013 p. 157-158
Alt SeriesEarth Sciences Sector, Contribution Series 20120412
PublisherGeological Association of Canada - Mineralogical Association of Canada (GAC MAC)
MeetingGeological Association of Canada - Mineralogical Association of Canada Joint Annual Meeting; Winnipeg; CA; May 22-24, 2013
File formatpdf
Lat/Long WENS -78.5000 -78.0000 45.0000 44.7500
Subjectsenvironmental geology; uranium; uranium deposits; mineral occurrences; mineral deposits; mineralization; rare earths; radionuclides; tailings; tailings analyses; tailings geochemistry; pollutants; heavy metals contamination; Bicroft Mine
ProgramTools for environmental impacts and adaptation for metal mining, Environmental Geoscience
LinksOnline - En ligne
AbstractUranium (U) tailings pose complex environmental risks because of their: large volumes; long-lived radioactivity; and their potential to release radionuclides, metal(loid)s, radon gas, and milling reagents into the surrounding environment. The primary objective of this study was to characterize the processes controlling the release, transport, and fate of U, its daughter products (226Ra, 210Pb), and rare earth elements (REEs) in a stream and retention pond system 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, 158 and has recently been the focus of renewed exploration as a source of REEs and other strategic metals. Samples of tailings, sediments, and surface waters were collected from the Bicroft Mine between 2010 and 2012. Regional-scale sampling of sediments, waters and soil gas radon, 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 14 mg/kg). However, much higher concentrations were found in stream and pond sediments below the tailings impoundments (31 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). Soil gas radon measurements show regional values from 3.2 to 48 kBq/m3
(mean 17 kBq/m3), with higher values in soils near U-REE mineralization (up to 770 kBq/m3) and in tailings from the Bicroft Mine (1800-12,000 kBq/m3). Seasonal sampling of effluent from the tailings impoundments in 2011 shows that the concentrations of U and 226Ra are
generally lower in the summer than in the fall. The filtered (<0.45 µm) concentration of U in stream water draining the Bicroft site was 7.6
µg/L in June compared to 25 µg/L in October. Similarly, the concentrations of 226Ra were 0.40 Bq/L and 0.72 in June and October, respectively. These observations provide improved understanding of the long-term stability of U tailings, and have implications for the
design of environmental monitoring plans. The results of this study are being used to develop improved guidelines to reduce the environmental risks associated with any future development of U-REE granitic pegmatite-hosted deposits.