MRNF Sites (Manitou and Preissac Molybdenite)

The visit will allow participants to discover two former mining sites currently being restored, under the responsibility of the Ministère des Ressources Naturelles et des Forêts (MRNF). 

• Manitou :  

“The Manitou site, located east of Val d’Or, was mined between 1942 and 1978, producing 7.5 million tonnes (Mt) of zinc, silver, and lead ore, as well as 3.6 Mt of copper ore. During this period, 11 Mt of acid-generating mining waste were deposited in two tailings ponds, without proper containment. 

The site was classified as an ‘abandoned mine site’ in 2002, following the bankruptcy of the last operator. Therefore, this site is listed under the environmental liability from mining and is an integral part of the ministerial work plan for the restoration of abandoned mining sites. 

When the site was taken over by the Ministère des Ressources Naturelles et des Forêts, the tailings were primarily spread across three areas: tailings ponds A and B (43 hectares [ha]), the main spill zone (90 ha), and the Manitou Creek, which extended over a length of 6.5 kilometers (km), including the delta along the Bourlamaque River (52 ha). The total area of land disturbed and contaminated by the presence of acid-generating mining waste represented over 200 ha. 

In 2006, an agreement was signed between the MRNF and Agnico Eagle Mines Limited (AEM) for the restoration of the Manitou site. The project involves using tailings from the Goldex mine to implement the raised groundwater technique with a single-layer cover. More recently, the construction of a capillary barrier cover over an area of 32 ha was initiated, where the deposition of Goldex tailings does not meet restoration objectives. Various vegetation techniques have also been used on the site since 2009. 

The visit to the Manitou site will provide an opportunity to discover the various restoration techniques implemented across all three tailings ponds, as well as the different monitoring activities conducted to track the performance of the restoration”. 

• Preissac Molybdenite : 

“The visit to the Preissac Molybdenite site will provide an opportunity to observe the progress of the restoration work carried out so far and to anticipate the challenges that still remain. 

Located about six kilometers south of the municipality of Preissac, the former Preissac Molybdenite mining site was operated for molybdenum and bismuth between 1962 and 1971. During this period, 2.2 million tonnes of ore were extracted and processed on-site, leaving behind a 2-hectare waste rock pile and an unconfined 12-hectare tailings pond. With no legal owner, the site is now under the responsibility of the MRNF, which is overseeing its restoration. 

Before the start of the restoration work, the site presented several environmental and structural challenges: unstable former underground workings, tailings and mining waste generating acid mine drainage and leachable, as well as contamination from dioxins and furans resulting from illegal burning activities carried out after mining operations.” 

Since 2011, various studies and interventions have been conducted to define and implement a tailored restoration plan: 

• In-depth studies: Environmental and biological characterization, geotechnical and geomechanical investigations, technical analyses 

•   Environmental rehabilitation (2020-2021): Excavation and treatment of mining waste, soils, sediments, and wooded areas contaminated with dioxins and furans. 

•   Stabilization of mining infrastructure (2024): Crushing of waste rock from the stockpile and injection as backfill, through boreholes from the surface, into unstable former underground workings.  

The next step, scheduled for summer 2025, will involve restoring the tributary of Lac Fontbonne by isolating contaminated sediments to protect the aquatic ecosystem. The overall site redevelopment, including the restoration of the tailings pond, is still in the design phase and will span the coming years. This visit will allow you to observe the progress of the work and better understand the challenges related to the restoration of an abandoned mine site. A unique opportunity to learn more about the environmental and technical issues of these interventions!