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TitleGeoenvironmental characterization of carbonatite tailings, Saint Lawrence Columbium Mine, Oka, Québec
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorDesbarats, A JORCID logo; Percival, J BORCID logo; Pelchat, P; Sekerka, J; Bilot, I; Girard, IORCID logo; Gammon, P
SourceGeological Survey of Canada, Open File 8753, 2020, 87 pages, Open Access logo Open Access
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedNRCan photo(s) in this publication
RelatedThis publication is related to Geoenvironmental characterization of ferroniobium slag, Saint Lawrence Columbium Mine, Oka, Québec
File formatreadme
File formatpdf; rtf; xlsx (Microsoft® Excel®)
NTS31G/08; 31G/09; 31H/05; 31H/12
Lat/Long WENS -74.1333 -73.9500 45.6000 45.4333
Subjectsenvironmental geology; hydrogeology; geochemistry; mineralogy; economic geology; geophysics; Nature and Environment; Science and Technology; Economics and Industry; groundwater resources; groundwater pollution; surface waters; water quality; environmental impacts; mineral deposits; metals; niobium; mining; mineral processing; concentrates; mine waste products; radioactive waste; tailings; tailings geochemistry; groundwater geochemistry; pyrochlore; meteorology; precipitation; pollutants; uranium; thorium; host rocks; bedrock geology; lithology; igneous rocks; intrusive rocks; carbonatites; trace element analyses; geophysical surveys; radiometric surveys, ground; radioisotopes; climate; physiography; boreholes; core samples; observation wells; grain size distribution; hydraulic conductivity; models; piezometric levels; Saint Lawrence Columbium Mine; Oka Complex; Mining industry; Waste water; Resource development; mitigation; Mitigation; Climate change; Methodology; cumulative effects; Water supply
Illustrationsphotographs; tables; satellite images; geoscientific sketch maps; ternary diagrams; profiles; time series; schematic cross-sections; plots
ProgramEnvironmental Geoscience Cumulative effects in cobalt watersheds
Released2020 11 19
Between 1961 and 1976, the St. Lawrence Columbium (SLC) mine produced pyrochlore concentrate and ferroniobium alloy from a carbonatite deposit near Oka, Québec. This report is concerned with the environmental characteristics of tailings generated by the processing of carbonatite ore at the SLC mine. It describes their physical properties, their mineralogy, their bulk chemistry and the chemistry of seepage draining from the tailings impoundment. Tailings solids were sampled at closely-spaced intervals in a borehole intersecting the full thickness of the impoundment. Tailings pore-waters were sampled in a nest of eight piezometers screened at different depths near the decant pond. Effluent was sampled at seepage points on the toes of the embankments of the tailings impoundment.
Grain-size distribution data for the tailings show that they range in texture from medium sand to clayey silt. The average water content, density, and porosity of the tailings are 30 %, 2.82 g/cm3, and 47 %, respectively. The geometric mean hydraulic conductivity of the tailings is estimated at 1.4 E-07 m/s using an empirical formula based on grain-size data.
The tailings are composed mainly of calcite (64-89 %) containing significant Sr, Mn, Mg, Ba, and REE. Other identified minerals include biotite (6-17 %), fluorapatite (2-22 %), chlorite (0-5 %), nepheline (0-2 %), magnetite, pyrite, sphalerite, and unrecovered pyrochlore. The fluorapatite contains high concentrations of REE although most of the REE inventory in the tailings is hosted by calcite. Most of the fluorine is hosted in biotite. The average total S content (mainly as sulfide) of the tailings is 0.53 %. In addition to Nb, the pyrochlore hosts U, Th, Ta, and Zr. Average U and Th concentrations in the tailings are 20 and 65 ppm, respectively.
Depth profiles of major ion pore-water chemistry show significant variations across the thickness of the impoundment as a result of several processes. In the shallow tailings, chemistry is controlled by calcite dissolution, sulfide oxidation and acid neutralization, which releases sulfate, Fe, Zn and Mo. At greater depths, oxygen is depleted and sulfate reduction occurs. Throughout the tailings, Ca, Mg, and Sr concentrations decrease with depth whereas Na and K concentrations increase steadily. This may be the combined result of nepheline hydrolysis and cation exchange. Fluoride concentrations increase with depth, approaching 25 mg/L. Aqueous concentrations of trace elements (U, Nb) in pore-water are very low and do not show any clear depth trend because of the low solubility of their mineral hosts. Total (aqueous and sorbed particulate) concentrations of REE reach 1 mg/L. The average pH and specific conductance of effluent from the tailings impoundment are approximately 8 and 1400 µs/cm, respectively. Effluent from the SE embankment contains 500 mg/L of sulfate, and fluoride concentrations of 8 mg/L, which exceeds the 0.12 mg/L guideline for the protection of freshwater aquatic life. Concentrations of U and other trace elements in tailings effluent are low.
This investigation of tailings at the former St. Lawrence Columbium mine, Oka, Québec, provides new geoscience data and knowledge useful for the environmental assessment of mining projects in carbonatite settings. This information will allow proponents and other stakeholders to anticipate potential environmental impacts associated with future resource development and to plan appropriate mitigation measures accordingly.
Summary(Plain Language Summary, not published)
New technologies are driving a strong demand for critical metals found in carbonatite deposits such as rare earth elements and niobium. However, little is known about the environmental characteristics of mine wastes from carbonatites. This study investigates the hydraulic properties, mineralogy, geochemistry, and drainage chemistry of tailings from the processing of niobium ore at the former St-Lawrence Columbium mine in Oka, Quebec. In addition to calcite, minerals found in the tailings include fluorapatite, biotite, diopside, pyrrhotite, and unrecovered pyrochlore. Potentially hazardous trace metals, including uranium and thorium, are sequestered within insoluble minerals. However, drainage from the tailings impoundment contains sulfate and fluoride at concentrations that may be harmful to aquatic life. Results of this study provide open access benchmark data for environmental impact assessments of carbonatite-hosted critical metal deposits developed in the future.

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