|Bruno Bussière, UQAT’s new industrial chair, is conducting mine site reclamation work on the abandoned Manitou site near Val-d’Or, QC. | Valerian Mazataud
The Université du Québec en Abitibi-Témiscamingue (UQAT) launched a new industrial chair this year exclusively dedicated to mine site reclamation. With $2.5 million in funding over five years, lasting until 2020, coming from the National Sciences and Engineering Research Council of Canada (NSERC) and industrial partners, the chair’s mandate is to develop efficient reclamation strategies that will limit mining’s environmental impacts. It will take over from UQAT’s previous chair on environment and mine waste management, which existed from 2001 to 2012.
For the Research Institute on Mines and Environment (RIME), which hosts new chair Bruno Bussière, a UQAT professor focused on waste management and mine site reclamation, the abandoned Manitou site is an ideal laboratory.
Of all the abandoned mine sites in Quebec, Manitou is by far the largest and most problematic. On the 200-hectare site, 15 kilometres from Val-d’Or, the cracked earth resembles a desert, with soil ranging in colour from pure white to dark orange. These tailings, which consist of sulphuric rocks, generate acid mine drainage (AMD) that has released heavy metals into the environment, and more precisely into the nearby Bourlamaque River. Aquatic life has been unable to survive in the river for decades along a three-kilometre segment downstream.
The former zinc and copper mine site, closed in 1979, was taken over by Quebec’s Ministry of Energy and Natural Resources after its last owner went bankrupt in 2003. In 2006, the ministry decided to cover the site with non-sulphuric tailings from Agnico Eagle’s Goldex Mine, some 24 kilometres away. The ministry began reclamation work the same year, with a plan to bury 11 million tonnes of sulphuric tailings. The previous chair had done research on the site in the hope of finding the best reclamation scenario. The first step was to dig 10 kilometres of drainage ditches to prevent the watershed from reaching the contaminated tailings.
The original plan was to cover the whole site with a 45 per cent liquid pulp from Goldex so that water from the pulp could drain through the tailings and raise the underlying groundwater level. After a while, groundwater would completely submerge the Manitou waste, thus blocking its contact with air and preventing oxidation.
However, the reclamation concept had to be revised after Agnico Eagle closed its Goldex mine in 2011 due to stability and infiltration problems at the mine. After the mine reopened in 2014, the tailings tonnage prediction was reduced. “In the centre of the pond, our calculations showed that we wouldn’t be able to raise the groundwater level enough to submerge the waste,” said Bussière, who has been doing research at Manitou since the 1990s as a graduate student at UQAT and was involved in the 2006 reclamation work. “So we convinced the ministry to change its method.”
Although a final decision has not yet been made, the plan eventually changed to building a cover with capillary barrier effects on the centre of the site. It will consist of three layers of different grain sizes that together are meant to prevent oxygen from reaching Manitou’s sulphuric wastes. Goldex is providing waste rocks of different grain sizes that will be reused as covering layers.
According to Bussière, reclamation planners should always consider using tailings and waste rocks from operating mines when looking for material. “Normally, Goldex would have put its tailings where it would have been easier and cheaper to put them,” he said. “They would have built a brand new tailings pond, while here we would be looking for natural materials, so in addition to reclaiming the Manitou site, we would also have to rehabilitate the places we would have stripped.” According to Bussière, mines that generate non-sulphuric waste represent invaluable opportunities for reclamation works.
Of the 713 abandoned mine sites in Quebec, 213 were in operation before their abandonment (the rest are exploration sites, or priority sites that have already been reclaimed). The total reclamation cost for all of the mine sites managed by the province is estimated to be $1.2 billion. The Manitou reclamation project alone has a total budget of $50 million and will go on until Goldex’s planned closure in 2024.
|The Manitou mine site is by far the largest and most problematic of the abandoned mine sites in Quebec | Valerian Mazataud
Challenges of revegetation
However, RIME does not focus solely on heavily contaminated sulphuric sites such as Manitou or Principal Mine, a 400-hectare mine site near Chibougamau in northern Quebec. It is also looking for efficient ways to revegetate both waste rock and tailings ponds, even ones that do not generate AMD. Mining regulations in Canada require that companies plant vegetation that can regenerate itself following mine closure.
Since 2010, Marie Guittonny-Larchevêque, a professor at RIME, has been reflecting on the best ways to reforest the waste rocks and tailings pond on the Canadian Malartic mine in Malartic, Quebec. The gold mine entered commercial production in 2011 and began progressive reclamation of its site as soon as 2013. The same year, Guittonny-Larchevêque began a series of experiments on reforestation of the steep slopes on the site.
“We know more or less how to revegetate flat areas,” she said. “On steep slopes though, little research has been done. You need to limit the impacts of erosion. The soil that you put at great cost will slip down slope if you don’t have the right vegetation to fix it.”
One common solution is to plant fast-growing herbaceous species on the slopes, such as clover, trefoil, fescue or rye grass, to lay down a green cover. The problem is that these plants are often hostile to trees. Guittonny-Larchevêque thus decided to try to plant fast-growing poplars instead, hoping that their roots could restore the soil quickly and prevent erosion so that other trees could establish themselves naturally. The poplars are doing fine so far, but a lot of research is still needed before she knows if they can fill reforestation objectives in the long run, she said.
Reclamation science is still young and researchers do not yet have the benefit of hindsight. More time is needed before they know whether these techniques will still be effective in 20, 50 or 100 years. This is why the mining industry has a direct interest in the new chair’s work.
RIME plans to train 20 undergraduate student interns in reclamation-related disciplines, in addition to hosting 16 master’s students, seven doctoral students and two post-doctoral students, all of whom will have access to mine sites to advance their work.
“Reclamation projects include characterization works and preliminary studies that can take a lot of time,” said Bussière. “Before moving on to the heavy works, we need to make sure that we found a sustainable solution. Having to come back in 20 years to start all over again is not an option.”
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