Backfill – The Other Tailings Storage Facility: Part 1

Promoting the Role of Backfill in Tailings Management

For many years, tailings management and mine backfill have largely been treated as separate processes.

The processing plant produces tailings continuously, while the backfill system intermittently produces the material required to support the mining cycle. The amount of tailings sent underground is often determined by the minimum volume of backfill required, with the remaining material directed to surface storage.

But is this still the right way to think about backfill?

As the mining industry continues to reconsider how tailings are managed, there is an opportunity to take a more integrated view. Rather than considering backfill solely as a requirement of the mining method, strong leadership will also consider it to be a key part of the mine’s overall tailings management strategy.

In other words, backfill can become the primary tailings storage facility.

Looking at the whole tailings system

In 2016, Rob Brown from Paterson & Cooke presented a simple challenge to the industry: as backfill engineers, designers and operators, we should continue looking for better ways to put more tailings back where they came from, underground.

The principle behind this was straightforward, striving to reduce the surface footprint and, with it, the associated risks.

At the time, tailings were commonly deposited in surface storage facilities as slurry or paste, while underground backfill was generally produced, often begrudgingly, as a necessary evil and only in the quantities required to support the mining cycle. The two processes were often planned and operated largely independently.

This approach can overlook an important opportunity. The approach that Rob suggested in 2016 was to look to consider backfill and tailings as parts of the same overall system and even turn it upside down in some cases; underground backfill is the primary storage system and surface storage used only as a last resort.

This does not mean that all tailings can, or should, automatically be placed underground. However, it does mean that the question should extend beyond simply determining the minimum amount of backfill required for ground control.

A more useful question may be:

How much of the tailings produced by the mine can practically be returned underground?

A changing approach to tailings management

Over the past decade, tailings dam failures have brought renewed attention to the risks associated with the storage and long-term management of mine tailings.

These events have reinforced the need for the mining industry to continually examine how tailings are generated, stored and managed throughout the life of a mine.

While surface tailings storage facilities will continue to play an important role at many operations, the industry is increasingly considering ways to reduce the volume of tailings requiring long-term surface storage.

This is where backfill can contribute.

By returning suitable tailings underground, backfill can reduce the quantity of material that needs to be stored on surface. Backfill should not be viewed as a replacement for responsible tailings management or as a solution to the risks associated with poorly designed or operated storage facilities. Instead, it can form part of a broader, integrated strategy aimed at reducing reliance on external tailings storage.

As backfill engineers, designers and operators, our role is not simply to design systems that produce enough fill to support the mining cycle. By developing reliable systems capable of consistently placing more suitable tailings underground, we can help mines capture more tailings underground through higher utilisation, while reducing the volume of tailings requiring surface storage and contribute to a broader shift towards more integrated tailings management.

The challenge is to find safe, practical and economically viable ways to put more tailings back where they came from.

Moving beyond the perception that backfill is a burden

Historically, backfill has often been perceived as a necessary burden of underground mining.

Backfill systems require capital investment. They consume energy and, in the case of cemented backfill, require binder. Designing and operating a reliable backfill system can also be complex.

At the same time, tailings sent to surface storage can appear to be low cost, out of sight, with an almost endless lifespan.

The true cost of surface tailings storage is rarely fully accounted for and can extend beyond simply transporting material to a storage facility. Depending on the operation, it can include the cost of TSF design, permitting, construction and expansion, dam management, water treatment during operations and after closure, rehabilitation and long-term monitoring.

There can also be consequences underground when the mine is unable to fill stopes at the required rate. Unfilled voids can affect the mining sequence, lead to expensive dilution and, in some cases, contribute to production delays.

When these factors are considered together, the comparison between backfill and surface storage becomes more complex.

The question is no longer simply:

What does it cost to make backfill?

It becomes:

What does it cost to manage tailings and maintain the underground mining cycle over the life of the operation?

This requires a whole-of-mine perspective rather than evaluating the backfill plant as a standalone cost centre.

Putting more tailings underground with realistic expectations

The objective is not necessarily to eliminate surface tailings storage.

Once rock has been excavated, crushed and ground into tailings, its volume increases; the swell factor. This means that there is not always sufficient underground void space to accommodate all of the material generated by the mine.

Surface storage will therefore continue to play a role at most operations.

The opportunity is to avoid treating surface storage as the default destination for tailings.

Instead, mines can examine where the practical limits of underground placement lie and make a conscious decision about how much tailings should be returned underground.

The goal is to push those limits where it makes technical, operational and economic sense.

Integrated tailings management is not a new idea

Below are just two examples of mines that have incorporated backfill into their broader tailings management strategies.

At the Louvicourt Mine in Québec, mine closure and environmental protection were incorporated into the mine design using the principle of “Design for closure, operate for closure.”

The tailings management strategy included both underground cemented backfill and surface deposition. Approximately 55% of the tailings were planned to be returned underground as cemented backfill, while the remaining 45% were deposited on surface.

This provides an early example of a mine deliberately considering underground backfill and surface tailings storage as complementary parts of the overall tailings strategy.

Another example is the Éléonore Mine in Québec, where the mine’s environmental requirements included restrictions on the discharge and storage of sulphide tailings in the environment. As a result, the operation investigated ways to incorporate the high-sulphide tailings into its paste backfill while achieving the strength requirements necessary for the mining operation.

The pyrite-rich tailings are concentrated and returned underground as paste backfill, while the non-sulphide tailings are stored on surface.

These examples illustrate an important point: integrated tailings management does not necessarily mean treating every tonne of tailings in the same way.

Different tailings streams, material characteristics, environmental requirements and mine conditions may lead to different disposal strategies.

The key is to consider these options together rather than designing the tailings and backfill systems independently.

The role of backfill is expanding

Over the past decade, the mining industry has placed greater emphasis on the lifecycle management of tailings and on considering alternative technologies and strategies.

This has created a stronger focus on integrated approaches to tailings management and on reducing the volume of tailings and water placed in external facilities.

For backfill engineers and operators, this changes the context in which backfill systems are designed and managed.

The backfill system needs to be considered not only in terms of its ability to meet strength and production requirements, but also in terms of its ability to reliably divert tailings underground.

The operational challenge

The idea of returning more tailings underground is simple.

Making it work can be considerably more complex.

A mine may have sufficient underground void space and more than enough tailings available to produce backfill yet still struggle to place enough material underground. Availability, utilisation, mine scheduling, stope preparation and operational downtime can all limit the amount of tailings that are ultimately diverted.

This leads to the next challenge.

If backfill is to play a larger role in tailings management, the industry needs to focus not only on how much fill the mine can get away with, but rather how much tailings can the underground take?

In Part 2 of this series, we examine the operational challenge of maximising underground tailings placement and why the answer involves much more than simply increasing paste plant capacity.

About this series

Backfill – The Other Tailings Storage Facility explores the evolving relationship between mine backfill and tailings management, based on Maureen McGuinness’s keynote address at Minefill 2026.

Next in the series:
Part 2: Maximising Underground Tailings Placement – The Operational Challenge