Geochemistry of Tailings from the Mount Polley Mine, British Columbia

To support remedial decisions for the Tailings Storage Facility breach at the Mount Polley Mine (MPM), a geochemical characterization program assessing the metal leaching and acid rock drainage potential of the tailings and other materials released into Polley Lake, Hazeltine Creek, and Quesnel Lake was performed. Because the tailings and other materials settled under subaerial conditions along the banks of Hazeltine Creek and in subaqueous conditions in Polley and Quesnel Lakes, the geochemical characterization assessed reactivity in both terrestrial and aquatic environments. Tailings and other materials deposited in these areas were found to be consistently non-acid generating indicating that weathering conditions are expected to be pHbasic under all depositional conditions. Leaching potential of tailings in subaerial environments was low and the potential for oxidative and reductive dissolution under deep water conditions was found to be negligible. Sub-aerial copper leaching is likely controlled by mineral solubility, which will limit loadings to the environment and can be used to inform remedial decisions.

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