Tailings plans that manage future risks
Sometimes it seems that the environmental and social expectations placed on the global mining sector are changing at the blinding speed of a slap shot. Yet even as Gretzky went on to become “The Great One” because of his ability to see patterns in the on-ice action and predict where they would lead — so he could get there first — members of the mining industry should consider proactive planning to meet the changing expectations of society.
For mines, some of the greatest changes are being felt in tailings management. This is because the lives of successful mines are measured in decades, and mining companies need to meet the expectations of society as they evolve over the mine’s lifetime.
Gretzky-like mining companies need to estimate where their “puck” will be — the puck being regulatory requirements for tailings management — many years into the future.What is acceptable to regulators, political leaders and other stakeholders currently will likely no longer be acceptable in the near future.
For a glimpse of the future for tailings management, consider occupational health and safety standards. Most mines target zero injuries or deaths on the job. Deviations from this goal are cause for concern. At the same time perfection is sought, however, employers realize that it is not always reached and so have developed emergency-response capability to deal with exceptions when they occur.
In mines management programs, an equivalent goal might be reducing the discharge of tailings-impacted water.
However, as with an injury on the job, there is almost always the possibility of a large or even catastrophic discharge. Tailings impoundment systems may be designed to contain a 50-year flood — but with increasingly unstable weather patterns, what happens when the 100-year storm comes along? Like OH&S programs, the impoundment system must be designed to deal with the larger-than-design event.All impoundment systems must be equipped with an emergency spillway that will allow for some controlled discharge, while preventing the overtopping of a dam. Only a very few specially designed tailings dams are capable of withstanding overtopping flows without failing catastrophically. A properly designed emergency spillway can greatly reduce the risk of a dam burst that would release a catastrophic flood of tailings and tailings- impacted water.
Managing tailings risk in future will also likely mean a larger role for thickened tailings. Compared with tailings that are deposited by conventional slurry methods, thickened tail- ings exhibit little particle segregation. This reduces the ingress of oxygen, which could lead to acid generation in acid-containing tailings. Thickened tailings also shed more water, thus reducing the flow of water through the tailings mass.
As well, we may see greater emphasis on the separate disposal of mine wastes that are of greater environmental concern (typically due to their geochemistry), so that more benign materials can be treated more cost-effectively, reducing overall costs.
It is not uncommon for mine waste facilities to be in operational service for a decade or less, after which they must be closed out. The “design life” for closure is normally much longer than that for the production life.At closure, it is often necessary to upgrade existing facilities to withstand seismic events or floods of much longer return periods than those that were used for the operational life. It is usually more cost-effective to adopt a “design for closure” approach and to build the facilities for long return period events in the first instance, as this avoids the need for large capital costs for closure upgrades just when the mine is going out of service.
Financial sources such as banks increasingly look for evidence that companies are managing risks effectively, and that includes risks stemming from tailings.Merchant banks signatory to the Equator Principles — and signatories now provide some 85% of project lending worldwide — in effect expect First World environmental and social practices to be followed in all projects they support in amounts over US$10 million.Even as the puck in a hockey game keeps moving, those standards keep getting tighter.A new version of the Equator Principles came out this year and is much more aggressive than the last one. As well, if risks are poorly managed, investors may avoid the company’s shares, and the company’s owners may have difficulty selling an otherwise-promising operation. It may also mean higher insurance rates and legal costs.
Just as Gretzky’s study of hockey-game patterns was an investment that paid off well during his on-ice career, investment in future-proof tailings plans can be a source of strategic advantage for a mining company.
John Boyd, P. Eng., is a principal in the Mississauga, Ont., office of Golder Associates Ltd. He is currently president of the Genevabased International Federation of Consulting Engineers (FIDIC). Contact: 905.567.4444; [email protected].
Ken Bocking, P.Eng., is a principal in the Mining practice of Golder Associates Ltd., based in the Brisbane, Australia, office. Contact: [email protected].