| Source | Proceedings of El1: The Transport and Fate of Contaminants in the Natural Environment, GAC-MAC Annual Meeting, Kingston, May; Geological Association of Canada-Mineralogical Association of Canada, Joint
Annual Meeting, Programs with Abstracts vol. 40, 2017.  Open Access |
| Abstract | Global demand for modern technology has increased the requirement for critical metals including rare earth elements (REE), platinum-group elements, niobium, tantalum, indium and tungsten. These elements
are used in components in high tech devices, and in development of green and defence technologies. In Canada, the supply of these elements is limited to a few deposits that are currently being mined (Niobec (Nb), St. Honoré, QC ) or under development
(e.g., Aley (Nb) in B.C.; Nechalacho-Thor Lake (Nb, Ta, HREE) in NT; Hoidas Lake (Nd) in SK; Eldor (Nb, Ta, REE), Kipawa (HREE), Montviel (REE), and Strange Lake (HREE) in QC). These deposits commonly occur in carbonatite or peralkaline granite
rocks, have complex mineralogy, and are associated with the radioactive elements U and Th.
To better understand the potential effects from mining REE and other critical metal deposits, a study was initiated at the GSC as part of the Environmental
Geoscience Program aimed at determining risks from metal mining. The St. Lawrence Columbium Mine in Oka, QC, formerly one of the largest Nb producers in the world, afforded a good proxy to examine long-term environmental effects. This open pit and
underground mine operated between 1961 and 1977 and produced 3,536,200 tonnes of Nb-bearing ore (average grade 0.51% Nb2O5) and 3,857,350 t of waste material. Annual production of concentrates containing ~ 52% Nb2O5 was ramped up to 2.25 million kg
from 113,000 kg in the early seventies (Gold et al., 1986). The Oka site is composed of a carbonatite and alkaline rock complex contemporaneous with the Monteregion Hills. Over 70 minerals have been identified and this complex is the type locality
for two minerals (niocalite and latrappite). The complex is formed largely of silica-undersaturated rocks of the melilitite and nepehelinite series. Niobium occurs in pyrochlore group minerals in sövite, a calcite-bearing carbonatite.
This study
focusses on the geochemical and mineralogical controls of metal mobility. To this end, representative rock samples, tailings, and waters from the open pits, tailings, decant pond and local creeks are being analysed. Representative rock samples were
collected from large waste rock piles and tailings samples were collected from two sites at 5 and 30 cm depths each. Preliminary mineralogical analyses by XRD show tailings are rich in calcite (~90 wt%) with minor to trace amounts of apatite,
niocalite, perovskite and pyrochlore. Rock samples contain abundant calcite with variable amounts of gypsum, apatite, mica (biotite/phlogopite), chlorite, amphibole, garnet, pyroxene and zeolite group minerals. Some samples contained sufficient
pyrochlore to be detectable in a calcite-rich sample. Slag material in the central area of the mine site is dominated by high-temperature hibonite and grossite along with vesuvianite, as well as minor amounts of augelite, bredigite, cristobalite,
perovskite, thorite and uraninite (not in order of abundance) interspersed in a glass matrix. The concern from this site is the radioactivity of thorium and uranium and their possible mobility along with other critical metals. The mineralogical
footprint of this site is complex and its characterization will aid in determining the mineralogical and geochemical controls of the contaminants. Lessons from Oka will be applied to deposits currently under development. |