Old tailings may be more than an environmental liability; with the right evidence and engineering, some could become secondary mineral resources.
A tailings dam built for copper decades ago may still contain cobalt. The miners did not necessarily miss it. Cobalt may not have been the product they were paid to recover, its concentration may have been uneconomic at the time, or the available processing technology may not have been able to separate it.
Change the market, the technology and the minerals a country considers strategically important, and yesterday’s waste can begin to look like tomorrow’s ore.
That possibility is driving interest in secondary prospectivity: the search for previously overlooked mining opportunities in waste from operating, closed and abandoned mines. For Australia, the opportunity is difficult to ignore. The University of Queensland estimates that Queensland alone holds at least 3,000 million tonnes of waste rock and 1,250 million cubic metres of stored tailings.
What could still be hiding in tailings?
Mines have traditionally been designed around one or a few principal commodities. Other elements entering the plant may have reported to tailings because there was no market for them, no requirement to measure them or no viable recovery circuit.
This matters because about half of the minerals on Australia’s Critical Minerals List commonly occur as co-products or by-products of commodities such as copper, zinc, lead, nickel and aluminium. Gallium, germanium and indium, for example, can occur in zinc deposits but may not be captured during processing.
There are more direct examples. University of Queensland researchers note that cobalt was historically recovered from Mount Isa copper ores but has also been sent to mine waste. Their work is investigating whether retreatment could recover the metal while reducing the environmental risk posed by the waste.
The material is already mined, crushed and sitting at the surface. That can remove some of the cost and disturbance associated with extracting fresh rock. It does not, however, make recovery simple.
A map is not a mineral resource
Geoscience Australia’s Atlas of Australian Re-mining Potential brings together information on tailings, waste rock, smelter residues and other mine wastes across the country. Its underlying database links waste features to their locations, storage types, source deposits and known commodities. Where information is available, it also records volume and rehabilitation status.
The Atlas gives engineering professionals and researchers a valuable place to start. It does not prove that every marked site can be mined again.
Historical tailings are rarely uniform. The upper layers may have weathered for decades, while deeper material remains chemically different. Valuable elements can be locked inside quartz or clay, attached to sulphide minerals, or spread through particles too fine for conventional separation. A promising assay result therefore answers only one question: what is present? Engineering professionals must still determine where it sits, how it is bonded and whether it can be liberated at a useful recovery rate.
That work requires drilling and representative sampling, followed by geochemical and mineralogical analysis. Resource models must also account for how the tailings were deposited, moved and altered over time. Without that characterization, a processing plant risks being designed around an average sample that does not represent the facility.
How would the minerals be recovered?
The recovery route depends on the material. Tailings may first be excavated or hydraulically reclaimed, screened and separated by particle size. Conventional methods such as gravity separation, magnetic separation or flotation can then concentrate minerals with suitable physical or surface properties.
For metals dispersed at low concentrations, hydrometallurgy may be needed. This can involve leaching the tailings, then using solvent extraction, precipitation or ion exchange to separate the target metal from the resulting solution. A 2025 review of critical-metal recovery from mine tailings also highlights bioleaching and organic acids as emerging alternatives, although their cost and performance at industrial scale still require careful testing.
The best flowsheet may combine several methods. Just as importantly, it must deal with what remains after recovery.
The environmental gain is not automatic
Re-mining can reduce the volume of legacy tailings, recover water and help fund rehabilitation. It may also allow old material to be placed in a newly engineered storage facility built to modern standards. Commonwealth Scientific and Industrial Research Organisation (CSIRO) has argued that long-term storage should be the last option considered, alongside further processing, water recovery and ways to reduce tailings at the source.
Yet disturbing an old facility can expose sulphides, release contaminated dust or water, and create a fresh residue stream. Flotation chemicals, acids and solvents bring their own handling and treatment requirements. A project that consumes excessive energy and water, or simply moves hazardous material from one dam to another, may offer little environmental improvement.
No waste disappears; it changes form. A credible project therefore needs a complete mass and water balance, geotechnical assessment, life-cycle analysis and rehabilitation plan. Mineral recovery and site remediation must be designed together.
A new engineering problem built on old material
Australia’s Critical Minerals Strategy 2023–2030 calls for more domestic processing, stronger environmental performance and a skilled workforce. Re-mining sits at the intersection of all three.
It will require geologists who can model unconventional deposits, metallurgists who can build selective flowsheets, civil and geotechnical engineers who understand ageing storage facilities, and automation specialists who can monitor variable feed and water conditions. For professionals preparing for this work, applied pathways such as EIT’s mining and resources engineering courses can help connect those disciplines with current industry practice.
So, can yesterday’s mine waste supply tomorrow’s critical minerals? In some cases, yes. However, tailings should not be treated as ready-made ore reserves. The real opportunity is to screen widely, characterize rigorously and advance the sites where recovery can strengthen mineral supply while leaving the land and water in a demonstrably safer condition.
References
Atlas of Australian Re-mining Potential | Geoscience Australia
Australian Mine Waste Database | Geoscience Australia
Critical Mineral By-product Potential | Geoscience Australia
Mine Waste Transformation through Characterisation | The University of Queensland
Tailings, an Emerging Market Opportunity | CSIRO
A Review on the Recovery of Critical Metals from Mine and Mineral Processing Tailings: Recent Advances | Journal of Sustainable Metallurgy
Critical Minerals Strategy 2023–2030 | Australian Government Department of Industry, Science and Resources
This article was published September 8th, 2026 and the content is current as at the date of publication.
