Australia’s resources sector is racing to replace high-risk brownfields with self-sustaining landforms engineered for the future.
For decades, mine closure was often treated as an afterthought. Fill the hole, cap the waste, plant some vegetation and move on. The problem is that natural systems are dynamic: slopes erode, drainage lines migrate, vegetation communities change and water reshapes land over time.
But with almost 240 Australian mines projected to close by 2040, demand is growing for innovative and cost-effective mine remediation methods that mitigate environmental, social and economic risks.
In Australia, the shift is visible in both practice and regulation. For example, Queensland now requires operators to submit final landform designs linked to proposed post-mining land use, supported by modelling of long-term stability.
Irene Chan FIEAust CPEng, Principal Geotechnical Engineer at PSM, stresses that closure engineering is multidisciplinary.
“The engineering design of a post-mining landform is often complex and requires input from a broad range of disciplines to address aspects such as geotechnical stability and settlements, surface water, groundwater, geochemistry, erosional stability, soil science and revegetation,” she told create.
She notes that these technical questions are inseparable from broader design considerations, and that it is important to understand how the different elements interact in order to achieve the optimal closure design outcome that satisfies the design intent.
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Landform design
The major change in mine remediation in the last decade or so has been around intent. Regulators are no longer asking whether a site looks neat at the point of closure; they are asking whether it can perform without ongoing intervention long after the operator has left, and for a myriad of proof-points starting before ground is broken.
Walter Weinig, Discipline Leader of Hydrology and Mine Closure at Stantec, described the earlier approach to mine closure as one that was often treated as the final step rather than planned for from the outset.
“Until more recently, the idea of mine closure was very much ‘the last person out locks the gate’,” he said. “In some cases, particularly historically and among smaller operators, sites ceased operating without a clearly defined long-term closure strategy. Responsibility for the land could then revert to the Crown or the state, depending on the original tenure, leaving a legacy of unresolved issues.
“But it’s been really nice to see in the last 10-15 years that we’re being more intentional about mine closure and thinking about what that end game really is, instead of leaving that to the next people.”
Weinig said post-mining land use is now part of feasibility planning and operational procedures, a shift prompted by the “recognition of the magnitude of the liabilities” as well an increasing acceptance that more planning up front makes a significant difference to costs at the back end.
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Natural lessons
Geomorphic landform design starts from a simple premise: no natural slope is perfectly static, so a successful post-mining landform should not be designed as if it will never change.
Weinig believes there has been a lot of progress in geomorphic landform design and models in the last five years, using them to guide activities during operations to help reshape the landscape to blend into the surroundings.
“It doesn’t necessarily restore the exact shape as it was before mining, but it blends in, and we use the natural landforms and natural areas as good analogues because they’re stable, so maybe we can make this stable also – learning from what nature is giving us.”
A key consideration is what is meant by the term “stable”.
“In a strict geomorphic sense, no natural slope is truly static,” Chan said. “All landscapes evolve over time as they respond to weathering, erosion, vegetation changes and gravity processes. Even undisturbed natural slopes undergo gradual change over time.
“For this reason, geomorphic landform design is not about creating a landform that never changes, but to create a landform that can evolve in a manner similar to the surrounding natural landscape.”
She said that, in practical terms, geomorphic design tries to replicate the geometry, drainage patterns and surface processes of natural catchments so the landform responds to rainfall and runoff in a way that is consistent with the surrounding environment.
“Although soil and rock properties are important, water is usually the dominant control on long-term performance, both with respect to erosional impacts and the potential influences on slope pore pressures. Rainfall intensity, runoff concentration, catchment hydrology, groundwater conditions and vegetation establishment are often the key factors that determine whether a landform remains resilient over time.”
By the numbers
Weinig reaches the same conclusion, saying that “a lot of the hurdles revolve around water”, especially where climate change adds uncertainty to extreme events, water quality and downstream impacts.
Overall, the practical challenge is that closure design must respond to local materials and climate rather than force a standard template onto every site.
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Negative legacies
Mine Closure Management Services’ Harley Lacy said most mine landforms lack integration with the natural ecosystem and landscape they inhabit, and impact as negative legacies.
“If some of the current landform design practices continue, many of these landforms will be prone to failure, bringing ongoing problems for the resources industry. In parallel, social outrage against mining will continue unabated as society will rightly feel vindicated in calling for greater regulation.”
It would be ideal to have zero impact, but Weinig said it is more realistic to think about what that post-mining land use is going to be and work towards that.
“It’s not necessarily restoration of the land to exactly as it was, but to what may be a beneficial use in the future, recognising the impacts that the mine is potentially going to have.”
Lacy believes that in Australia’s arid lands and marginal farmlands, we rarely see a use for final voids because there is no human population at a scale to attract the capital required for conversion, so they remain brownfields and, in many cases, abandoned.
However, one remote project has become the poster child for repurposing mine sites.
Genex’s Kidston Pumped Storage Hydro Project in Northern Queensland was a world-first when the former gold mine was transformed into a natural energy hub.
CEO Craig Francis described Kidston as a case where an old gold mine’s liabilities became the basis of a new industrial asset providing sustainable energy generation and storage.
“There were two giant open pits,” he said. “One was about 300 m deep and full of water already, and the other one was shallower and surrounded by revegetated waste rock dumps. They were very close to each other, which meant that you could have short waterways connecting, so it’s lower-cost there.”
Just as important, he said, was the inherited infrastructure: “There was construction power supply, a dedicated water supply, accommodations for workers, an airstrip – it ticked a lot of boxes in that regard.”
The concept of the scheme is to construct a dam on top of the shallower pit using existing waste rock dumps for the upper reservoir and connect this to the deeper pit as the lower reservoir via an underground power station and waterways.
The significant difference in water levels of the two reservoirs enables the generation of power when water flows from the higher pit to the lower pit via underground turbines and generators.
The system then operates in reverse to store water (or energy) by pumping from the lower reservoir to the upper reservoir in times of low electricity demand.
The project also combines solar – a 50 MW solar farm has been operating at the site since 2017 – and wind energy with a battery energy storage system to optimise dispatchable power supply.
“The tailings area had already been capped; it was flat, elevated, so there’s no shading from any trees, and it was homogeneous material too, because of the rehabilitation,” Francis said. ”That made it suitable for a 50 MW solar farm.
“We bought the mine having been rehabilitated, with the long-term obligations to essentially retain water run-off within the site. We are in the process of moving into a different legislative regime, away from mining legislation to contaminated lands because of the long-term use with the pumped storage hydro project.
“Given the long-term industrial use, and that the water is being retained onsite centrally, we think it’s an appropriate juncture to do that.”
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Accelerating closure
Mine closure still depends heavily on earthworks, water management and vegetation establishment, but technology is changing the speed at which those tasks can be completed and verified.
Lacy noted that over the last couple of decades, geomorphic restoration/geomorphic landform design tools, such as GeoFluv, and landform erosion models such as SIBERIA, have been proven as the most likely pathways to engineer and construct mine landforms to leave a positive legacy.
In a study of coalfields in the Hunter Valley by the University of Newcastle, GeoFluv design using SIBERIA modelling reduced erosion by half while being able to store 7 per cent more mine waste volume than contour banks. Additionally, the gullying pattern was predicted by the landscape evolution model, and 77 per cent of the eroded material was predicted to be deposited within the first-order subcatchments, significantly further reducing sediment yield.
GeoFluv is a design tool that recreates the drainage patterns and slopes of stable natural landscapes adjoining the potential remediation site, so it can perform more like mature terrain over the long term and promote the growth of flora and fauna.
It involves measuring slope gradients, channel dimensions and catchment forms, with the data fed into 3D design software to generate a network of ridges, valleys, swales and stream channels scaled to the site’s conditions and variable flows.
The final digital surface can be tested for cut-and-fill balance and then uploaded to GPS-guided earthmoving equipment for construction.
Meeting standards
If there is a single phrase that defines modern closure, it is the regulator’s expectation that the post-mining landscape be safe, stable and sustainable. But proving that is not straightforward.
Chan said the requirements are evolving and many of the state regulatory policies have been updated within the past five years, including creation of specific mine closure bodies, such as the Queensland Mine Rehabilitation Commissioner.
“Often in regulatory policy there is reference to the post-mining landscape being safe, stable and sustainable,” she said.
“While guidance on interpretation of this requirement does exist, it is still often subject to interpretation and alignment between a mine and the regulatory body depending on what is feasible for a particular site considering its unique conditions. This highlights the importance of establishing acceptability criteria for different aspects at the outset of mine closure planning.
“This is complicated by the fact that each site is unique and there isn’t a tick-box list of requirements to allow relinquishment of a mining lease upon closure – and the outcome requirements, monitoring approaches and establishing a proof of performance are all subject to interactions with the applicable state regulator.”
Australia’s standards are still largely state-based, but several interviewees describe clear progress. Weinig said parts of Australia are now “as good as anywhere else around the globe” in how proactively they think about post-mining land use and closure metrics.
Lacy is more cautious, arguing that standards have improved, but commercial pressures, fragmented bonding regimes and inconsistent enforcement still create gaps between best practice and what actually gets built.
However, he noted regulators are pointing the way. In 2021 the NSW Resources Regulator published a guide “identifying and adopting geomorphic design principles to achieve a natural and stable landform outcome”.
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Creating environments
The broader lesson is that mine closure is not separate from mine design. It is an extension of it, and a long-term extension at that. Rather than being about whether the environment is acceptable at handover, engineers are being asked to use natural analogues as design references to create environments that are likely to keep functioning for centuries as climate, runoff and ecological communities change.
The most advanced Australian closure projects are not trying to erase mining. They are trying to leave behind landforms with a credible future – self-sustaining, lower-risk and increasingly capable of supporting new ecological and social value.
Groundbreaking innovations
Algal biomass to address contaminated mine site water
Research by CSIRO and CRC TiME has discovered that various micro and macro algae found in mine waters can remove pollutants and sequester carbon dioxide. Algal biomass could also be used to suppress dust and improve plant growth as a fertiliser and biostimulant.
Dr Guy Boggs, CEO of CRC TiME, said water treatment and management of acid mine drainage remains a significant hurdle to successful transitioning to next land uses.
“If industry can capitalise on new technologies like algae and algal biomass to improve water conditions, this could help both risk reduction and value creation – key factors in transforming regions after mining.”
Tailings dewatering
The MudMaster – Phibion’s patented twin-screw amphibious machine – operates directly on soft tailings, mechanically removing interstitial water and increasing material strength. While improving density and shear strength, it also accelerates water recovery without the need for filtration or chemical treatment by leaving it on the surface to be pumped away and reused.
Phibion said these outcomes support safer storage, smaller footprints and preparation of land for life after mining.
Electrokinetic dewatering
Electrokinetic dewatering involves direct current voltage using two or more electrodes. Water flows towards the negatively charged electrode, the cathode, separating it from the sludge.
Although the technology is not new, its usefulness in mine tailings has been limited due to issues such as rapid corrosion of the anode, difficulties with collecting the water flowing to the cathode and loss of contact with the electrodes as the tailings dry.
Recently, forming conductive polymers into tubular wells around which a filter cloth is wrapped has solved the problem of water collection, and contact is improved with a greater surface area of the polymer electrodes. The lack of exposed metal also negated the corrosion issue.
Various research projects are underway to see how electro-osmosis dewatering can be used to enhance the strength of the tailings and support mine closure and reclamation processes.
