Mining Methods for Critical Minerals

Mining is the physical extraction of mineral-bearing rock or fluid from the Earth, and it represents the first major capital-intensive stage in the critical minerals supply chain. The choice of mining method depends on the depth, geometry, grade, and mineralogy of the deposit, as well as environmental, social, and economic constraints. For critical minerals, the diversity of deposit types means that nearly every known mining technique finds application somewhere in the value chain. Lithium is extracted from both hard-rock mines and brine evaporation ponds. Rare earths are recovered from open pits in carbonatites and through in-situ leaching of ion-adsorption clays. Cobalt is mined underground in the copper-cobalt belt of the Democratic Republic of Congo and as a byproduct of nickel laterite operations in Indonesia and the Philippines.

Open-Pit Mining

Open-pit mining is the most common method for large, near-surface critical mineral deposits. The process involves removing overlying waste rock (overburden) to expose the ore body, which is then drilled, blasted, loaded onto haul trucks, and transported to processing facilities. Open-pit mines can achieve enormous scale: the Bayan Obo rare earth mine in Inner Mongolia, China, the world's largest rare earth operation, is an open-pit mine that has been in continuous production since 1957. Similarly, the Greenbushes lithium mine in Western Australia and the Mopani copper-cobalt mine in Zambia use open-pit methods.

The advantages of open-pit mining include lower per-tonne extraction costs, higher production rates, and greater operational flexibility compared to underground methods. However, the environmental footprint is substantial. Open pits generate large volumes of waste rock and tailings, alter surface hydrology, and can create lasting landscape disturbance. Progressive rehabilitation, including backfilling, revegetation, and water treatment, is now a regulatory requirement in most jurisdictions, though enforcement varies considerably between countries.

Underground Mining

When deposits extend to greater depths or are too narrow for open-pit extraction, underground mining methods are employed. These include room-and-pillar, sublevel stoping, block caving, and cut-and-fill techniques. Underground mining is essential for accessing the deep copper-cobalt deposits of the Central African Copperbelt, the platinum group metal (PGM) reefs of South Africa's Bushveld Complex, and numerous hard-rock lithium pegmatites.

Underground operations face higher per-tonne costs due to the need for ventilation, ground support, underground haulage, and dewatering systems. Worker safety is a critical concern, particularly in artisanal and small-scale operations in developing countries where safety standards may be inadequate. The Kamoa-Kakula copper-cobalt project in the DRC, developed by Ivanhoe Mines, represents a new generation of large-scale underground critical mineral operations that aim to combine high production rates with modern safety and environmental standards.

In-Situ Recovery

In-situ recovery (ISR), also known as in-situ leaching, involves injecting a leaching solution into the ore body through a pattern of injection wells, dissolving the target minerals underground, and pumping the pregnant solution to the surface for processing. ISR is the dominant extraction method for uranium and is increasingly being evaluated for lithium, rare earths, copper, and nickel.

The technique is particularly significant for ionic clay rare earth deposits in southern China and Myanmar, where dilute ammonium sulfate or magnesium sulfate solutions are used to desorb rare earth ions from clay minerals. These ion-adsorption deposits are the world's primary source of heavy rare earth elements such as dysprosium and terbium, which are critical for high-performance permanent magnets. However, ISR of ionic clays has historically caused significant environmental damage, including groundwater contamination and soil degradation, prompting Chinese authorities to consolidate operations and tighten environmental standards.

Brine Extraction

Lithium production from continental brines, concentrated in the "Lithium Triangle" of Chile, Argentina, and Bolivia, employs a unique extraction approach. Lithium-rich brine is pumped from underground aquifers into large evaporation ponds, where solar energy drives the progressive concentration of lithium over 12 to 18 months. The concentrated brine is then processed chemically to produce lithium carbonate or lithium hydroxide. This method offers low energy costs but requires vast land areas, consumes significant water resources in arid environments, and has drawn opposition from local communities and environmental groups concerned about impacts on fragile high-altitude ecosystems.

Direct lithium extraction (DLE) technologies, which use selective adsorption, ion exchange, or membrane processes to extract lithium from brines without large evaporation ponds, are under active development by companies including Lilac Solutions, EnergyX, and Koch Technology Solutions. DLE promises faster extraction times, higher lithium recovery rates, and reduced water consumption, and could unlock brine resources previously considered uneconomic.

Environmental and Social Considerations

Mining for critical minerals carries significant environmental and social impacts that vary by method, scale, and jurisdiction. Acid mine drainage, tailings dam failures, deforestation, biodiversity loss, and water depletion are well-documented risks. The catastrophic tailings dam failures at Samarco (2015) and Brumadinho (2019) in Brazil, while associated with iron ore mining, have heightened scrutiny of tailings management across all mining sectors.

Social impacts include displacement of communities, conflicts over land rights, and labor practices in artisanal mining. An estimated 15 to 30 percent of the world's cobalt supply originates from artisanal and small-scale mining in the DRC, where child labor, hazardous working conditions, and lack of safety equipment remain persistent problems despite industry initiatives such as the Responsible Minerals Initiative and the Fair Cobalt Alliance. As demand for critical minerals grows, ensuring that extraction meets acceptable environmental and social standards is both an ethical imperative and a regulatory requirement that increasingly affects project financing and market access.

Permitting and Development Timelines

The time required to take a critical mineral project from discovery to production is a major constraint on supply responsiveness. In the United States, the permitting process for a new mine averages seven to ten years and can exceed 15 years when legal challenges arise. Canada and Australia have somewhat faster processes, typically five to eight years, but still face delays from environmental impact assessments, Indigenous consultation requirements, and community opposition. By contrast, some jurisdictions in Africa and Central Asia can grant mining permits within one to three years, though this speed may come at the cost of reduced environmental and social safeguards.

Recognizing that lengthy permitting timelines undermine the ability to diversify critical mineral supply, the United States, European Union, Australia, and Canada have all introduced legislative and regulatory reforms aimed at accelerating mine approvals for strategic mineral projects. These reforms must balance the legitimate need for speed with the equally legitimate need for thorough environmental and social impact assessment, a tension that will define the politics of critical mineral supply for decades to come.