The Pine Point lead-zinc mine, which operated from 1964 to 1988, included more than 50 open pits and associated waste-rock dumps, a mill site and concentrate loadout, a tailings impoundment area containing processing waste, and associated infrastructure. The pits, mill site, roads, waste-rock dumps, and powerlines were reclaimed to the standards in place at the time the mine closed, and the land leases were returned to the government. Teck Metals retained the lease for the tailings impoundment area to supply ongoing care and maintenance.
In 2017, the Mackenzie Valley Land and Water Board asked Teck to submit an updated closure and reclamation plan for the tailings area that followed revised guidelines the board had issued in 2013. The newer guidance was based on the closure principles of physical and chemical stability, no need for long-term active care, and compatibility with future land use.
Before a revised closure plan could be developed, more information about the site was needed to provide a better understanding of the fate and transport of zinc and other metals within the tailings area. Barr developed a multi-year research plan to study metal concentrations as well as the fate and transport of metals across the site. We also studied the watersheds and surface-water routing, groundwater conditions, and the water balance and geochemistry at the site, and conducted an assessment of human-health and ecological risks associated with the existing conditions. In 2018, the Mackenzie Valley Land and Water Board authorized the research plan for implementation.
Barr’s work began with reviewing the existing closure plan for the tailings area, which covers 2 square kilometers and contains 54 million tonnes of tailings from the mine. From there we identified the research activities and studies needed to resolve remaining uncertainties and data gaps, and developed a phased approach for implementing that work. The results of the research and studies is helping Teck choose the best overall closure option and further revise its long-term plan.
One field component of the research involved collecting environmental samples to obtain a better understanding of the tailings’ chemical and physical characteristics. Geochemical testing — aimed at investigating the potential for ongoing metals leaching due to the weathering of sphalerite and other trace minerals — included static testing, column leaching, and evaporative drying tests.
Data from the samples were incorporated into several desktop studies. Using the GoldSim platform, Barr developed coupled water-balance and fate-and-transport models that incorporated methods for evaluating closure options offering climate-change resiliency. That integrated modeling was key to informing development of the closure and reclamation plan. Other supporting studies are currently underway.
Engaging local Indigenous communities allowed Teck and Barr to learn what the communities envisioned for the restored site, including how it should look and what it should provide. Involving local communities early in the research process helped shape studies to address their concerns. For example, concerns related to the potential for dust generation have arisen in meetings and Barr has performed air dispersion modeling to assess potential risks and inform future decision making. In addition, we partnered with community members to collect samples of surface water and wild berries.
Barr prepared the research plan and revised the larger closure plan with the outcome in mind: long-term closure that is cost-effective, meets regulatory requirements, and addresses community concerns. Addressing high-level tasks up front and conducting work in phases has kept activities focused on the key issues, so that time and money aren’t taken up by noncritical pursuits.
Barr has also been supporting annual water-treatment operations at the site, including forecasting pondwater levels and the timing of spring melt so operators can schedule resources; evaluating the efficacy of the lime low-density-sludge process; and assisting with process optimization plans. In addition, we have bench- and field-tested several chemical aids to improve particle formation and settling.