Industry Best Practices for Mining Site Remediation

Mines and communities have been linked throughout our history. One of the many challenges when mines close is they leave behind mine physical hazards such as openings to surface (shafts, raises, adits, etc.) and near-surface workings (i.e., crown pillars overlying stopes, drifts, and tunnels). Safely closing these mine physical hazards can be complex, expensive, and often require in perpetuity maintenance requirements.

These mine physical hazards can present risks to the public (i.e., injuries and damage to property and infrastructure) if left un-rehabilitated. These mine physical hazards might have been a “lower risk” situation during operations or directly after closure but can become a high risk if they are left to degrade over the following years and/or decades often when the community has forgotten about them. Surface rights owners may even be unaware these mine physical hazards are on their property.

Over the years the remediation requirements for mine closure in Canada and many other locations have evolved and became more stringent, often due to past failures and the overall increased knowledge and experience of all parties involved.

This presentation will provide successful examples of locating, investigating, assessing long-term stability, developing specific risk mitigation and remediation measures for physical hazards of mines located in communities with historical mines.

This article discusses the management of geotechnical risks associated with abandoned mining sites, focusing on infrastructures related to mine tailings storage areas such as dikes, dams, ponds, and waste rock piles. In Quebec, there are over 350 abandoned mining sites, under the responsibility of the State making risk assessment related to the instability of storage facilities necessary for the ministère des Ressources naturelles et des Forêts (MRNF) of Quebec.

To ensure diligent management, the MRNF is implementing a risk management system based on best practices and international standards. The goal is to protect public health and safety and the environment while ensuring transparency and consistency in the management of abandoned mining sites under state responsibility.

The risk management system developed by the MRNF aims to manage the storage facilities of abandoned mining sites using resource optimization tools, communication support, a holistic, proactive, and integrated approach, and continuous improvement to reduce risks.

It is important to find a balance between risk reduction and the costs associated with these measures. It is unrealistic to aim for total risk elimination, as this could lead to excessive expenses and inefficient use of resources. However, it is also crucial not to underestimate the risks, as this could compromise the safety and well-being of surrounding communities. The management of abandoned mining sites under the responsibility of the State must be guided by a commitment to public and environmental safety, while being realistic about available resources and the management of public funds.

This article presents the initial steps in developing a geotechnical risk management system implemented by the MRNF for the storage facilities on abandoned mining sites, with the primary objective of providing a transparent, traceable, and reproducible decision-making tool to effectively inform authorities about the risks.

Environmental remediation to numerical standards is often unattainable in mining jurisdictions due to widespread naturally elevated metal concentrations in soils, bedrock, groundwater and/or surface water. The capacity to differentiate between natural and anthropogenic contamination due to a common source (metal ore) as a standard remedial objective is therefore limited in terms of technical feasibility, thus requiring alternative approaches.

This presentation discusses the opportunities for addressing the challenges of limited closure bonds to facilitate the closure of numerous abandoned/orphaned mine sites via strategic site screening, prioritization of investigation, contaminant delineation, human health and ecological risk assessment and implementation of risk management measures.

The closed Giant Nickel mine site is situated approximately 10 km to the north of the community of Hope, British Columbia. The site was operational from 1959 to 1974 and comprised an underground copper and nickel mine, a concentrator, and tailings storage facilities. Approximately 5 Mt of tailings are stored at the site in the Upper TSF and Lower TSF. In 1995, the tailings were covered with a layer of soil and the site was revegetated with native species. Following this intervention, the site was considered to be in a state of passive closure with limited monitoring, which did not require active water management. In 2002, the property came under the responsibility of Barrick Gold (Barrick) when it acquired the Homestake Mining Company.

In 2015, Barrick initiated a holistic assessment of the tailings facilities at the Giant Nickel site. The site closure strategy was updated to a configuration that is both physically and chemically stable, with the potential for alternative post-mining use. Further remediation work was conducted between 2017 and 2019, comprising the backfilling of both tailings sites to prevent water accumulation, the addition of stabilizing berms to the upper tailings site's east and south embankments, and the installation of a passive seepage treatment system. In 2023, the Giant Nickel tailings facilities became the first in Barrick's portfolio to achieve the designation of 'Safe Closure', as a result of the company's commitment to comply with the Global Industry Standard for Tailings Management (GISTM).

The assessment and mitigation measures encompassed a multitude of aspects, including geotechnical stability, the design of a passive seepage treatment system, the geochemistry of tailings and construction materials, and modifications to the water management plan. The investigations and environmental monitoring conducted on this site have enabled Barrick to improve its understanding of the site and refine the design of the remediation work.

This presentation will outline the multi-disciplinary and iterative approach adopted by Barrick at Giant Nickel to assess and mitigate the geotechnical and environmental risks associated with tailings facilities, as well as the process used to achieve the 'Safe Closure' designation.