Mine reclamation of older sites: Today’s Requirements

The Preissac Molybdénite site has been the subject of several data acquisition studies due to its past mining and industrial activities (roasting). These multidisciplinary studies (biology, ecology, environmental characterization, geotechnics, hydraulics, hydrogeology, etc.) were conducted throughout the development of the restoration project, from the data acquisition phase to preliminary engineering. They subsequently led to the development of restoration and rehabilitation concepts, implemented according to intervention priorities established based on safety requirements and environmental impacts. Restoration and rehabilitation work began in the early 2020s with the implementation of the solutions at the site and is still ongoing.

Historical mining sites constitute an industrial, environmental and territorial legacy whose reclamation requires approaches tailored to their long history. Designed and operated at a time when standards, waste management practices and stakeholder expectations differed significantly from current requirements, these sites present unique challenges. Reclamation therefore requires understanding, documenting and managing a complex legacy.

This presentation will draw on the example of Matagami, in Québec, to examine the issues associated with the closure and reclamation of a historical mining site. The analysis will focus in particular on reconstructing operational history, managing documentary gaps, evaluating residual risks and addressing aging infrastructure whose design may not meet current standards.

The presentation will also address the evolution of regulatory frameworks and environmental expectations, which can alter closure criteria over a site’s lifespan. These changes can increase uncertainty regarding closure plans, the scope of work, costs, financial guarantees, schedules and long-term monitoring obligations. They thus raise a central question for investment planning: how to manage the financial and technical risk associated with shifting government targets and standards?

Through the case of Matagami, emphasis will be placed on an integrated approach based on adaptive management, technological innovation, progressive site knowledge and dialogue with authorities and communities.

The Abitibi region and Northern Ontario form one of the most historically significant mining regions in Canada, with over a century of large-scale mineral exploration and production. The legacy of these mining activities is hundreds of mine works, such as mine shafts and other underground openings.

Rehabilitation work is often needed to secure these works that pose safety risks. Initial approaches to this work often seek to control the risks rather than manage the underlying causes. Comprehensive and integrated interventions—including a long-term vision aimed at eliminating hazards rather than simply mitigating them—yield numerous benefits for both host communities and the industry.

Planning the rehabilitation of mine works generally begins with a literature review, sometimes relying on limited historical data, to identify the risks. Field investigations make it possible to confirm initial hypotheses and develop tailored rehabilitation options.

This presentation addresses completed and ongoing rehabilitation projects in Abitibi and Northern Ontario. It discusses industry perspectives on the challenges of having limited historical information, considerations guiding the choice of investigation methods and field constraints encountered during the investigation and rehabilitation processes. It will demonstrate that effective rehabilitation aimed at hazard elimination relies on a tailored, risk-based approach that evolves as information becomes available.