One of the main reasons for starting to write posts on this website was to prepare for my viva or PhD defense. As you may not know, my PhD focused on the reactive transport and geochemistry of in-situ recovery of copper, also known as Cu-ISR. I find Cu-ISR and ISR in general quite fascinating. One of the biggest challenges of this technology, especially for Cu and other metals, is the lack of predictive reactive transport models that can accurately forecast recovery and financial success while ensuring minimal environmental disturbance. However, that’s a story for another post. In this intro post, I will introduce conventional Cu-ISR. We will explore later why I refer to hydraulic-driven Cu-ISR as “conventional,” but for now, let’s delve into the key concepts and see if I can convince you that Cu-ISR has great potential for future applications. Please note that most of this text is copied from my PhD thesis, so there may be some self-copyright infringement, but hey, free information is free information, right?

Let’s get started!

What is Cu-ISR?

ISR, also known as in-situ leaching (ISL) or solution mining, is a mining method that involves injecting a solution into the ground to dissolve specifically targeted minerals or metals. The solution, which is called a lixiviant, is typically an acid or a mixture between an acid and an oxidant1, although alkaline solutions have also been tested. The lixiviant is injected through a well into the ore deposit. As the solution migrates across the ore deposit, it dissolves the targeted minerals or metals, which are then transported to an extraction well. Therefore, ISR has the potential to significantly reduce landscape scarring, eliminate tailings dams and waste rock stockpiles, and minimise energy consumption and carbon emissions.

Cu-ISR

Why isn’t Cu-ISR more commonly used?

Despite its promise, Cu-ISR has primarily been applied to shallow ore bodies, predominantly uranium deposits, where the grades are relatively uniformly distributed. It appears to be less suitable for deposits with complex geometries or those located at great depths. One of the main limitations of Cu-ISR is the challenge of inducing rapid solution migration through ore bodies with very low hydraulic conductivity. As a result, while Cu-ISR has been successfully employed for uranium extraction2,3, it has not yet been widely adopted for other types of metal deposits. Another significant limitation of ISR is the potential contamination of groundwater and surrounding ecosystems if highly reactive chemicals injected into the subsurface are not properly managed. Therefore, to expand the application beyond uranium mining, it is crucial to gain a better understanding of its techno-economic feasibility for suitable copper deposits. This requires assessing the geological, hydrogeological, and mineralogical conditions under which Cu-ISR can be effectively and safely utilized. Enhanced understanding of these factors will not only address technical and economic issues but also contribute to increased public acceptance of Cu-ISR, wherever it proves to be a suitable method and maintains a social license to operate.

Cu-ISR Applications: Past and Present

Over the past decades, in-situ recovery has been extensively applied to uranium mining. In 2020, around 57 % of global uranium production was supplied by ISR4. The success of uranium in-situ recovery (U-ISR) can be largely attributed to the specific characteristics of typically mined uranium deposits. These are generally sedimentary deposits that possess sufficient hydraulic conductivity to permit the lixiviant to migrate sufficiently fast across them. Additionally, they are often hydraulically constrained, such that the migration of the lixiviant is easier to be controlled and directed towards the recovery well. U-ISR is the main mining method for uranium in Kazakhstan, Australia, China, Russia, Uzbekistan, and the United States. For example, Beverley and Beverley North (South Australia) are closed mines currently under care and maintenance status, and Four Mile is a current ISR mine in Australia. Those deposits are characterised by sand and gravel sediments, where the mineralization occurs at depths between 100 and 250 m5. U-ISR is becoming increasingly popular in other countries like Canada. For example, Denison Mines is currently developing the Phoenix deposit and conducting ISR testing with recovery rates of up to 97 %6.

For copper and other metals, however, ISR applications are sparse, and the outcomes in terms of recovery efficiency are far more diverse. Currently, no copper mines are using ISR in a full-scale operational mode. However, various test facilities have been set up, and several field trials have been undertaken with variable success. Examples of completed field trials include Casa Grande and Safford in Arizona (copper porphyry), Gunpowder in South Australia (copper oxides), and Chuquicamata in Chile (paleochannel). Examples of ceased mine operations include Mount ISA in Queensland (copper oxides) and San Manuel in Arizona (copper porphyry)2. Among all previous endeavours, the ISR operation at the San Manuel mine has been the most successful, reaching a production of 11,000 ton/yr at its peak7. In general, the crucial showstoppers for many of these projects have been (i) the lack of sufficient permeability and (ii) the loss of lixiviant through fractured zones of the targeted deposits. Currently, new tests are being undertaken in Florence (Arizona) and Kapunda (South Australia). Both projects target oxidised copper ore and have conducted advanced hydrometallurgical testing. Florence Copper has received environmental approval to inject lixiviants and is currently the most advanced copper ISR project. Overall, the majority of attempts to develop Cu-ISR projects have been undertaken for copper oxide deposits2. Even in San Manuel, the successfully exploited part of the porphyry corresponded to the oxidised shallower cap. However, to make ISR a more widely applicable and efficient mining technology, extending its use to copper sulphides is crucial. This is because most of the world’s copper reserves are found to be hosted by chalcopyrite, which is often found in the sulphidic zones of copper porphyries.

In the next series of blog posts, I’ll be talking about how reactive transport and numerical modelling can help make Cu-ISR a reality while assuring its environmental safety.

  1. Barton, I. F.; Hiskey, J. B. Chalcopyrite Leaching in Novel Lixiviants. Hydrometallurgy 2022, 207, 105775. https://doi.org/10.1016/j.hydromet.2021.105775. ↩︎

  2. Seredkin, M.; Zabolotsky, A.; Jeffress, G. In Situ Recovery, an Alternative to Conventional Methods of Mining: Exploration, Resource Estimation, Environmental Issues, Project Evaluation and Economics. Ore Geol Rev 2016, 79, 500–514. https://doi.org/10.1016/j.oregeorev.2016.06.016. ↩︎ ↩︎ ↩︎

  3. Sinclair, L.; Thompson, J. In Situ Leaching of Copper: Challenges and Future Prospects. Hydrometallurgy 2015, 157, 306–324. https://doi.org/10.1016/j.hydromet.2015.08.022. ↩︎

  4. IAEA; NEA. Uranium 2020: Resources, Production and Demand; 2020. https://www.oecd-nea.org/jcms/pl_52718/uranium-2020-resources-production-and-demand. ↩︎

  5. Government of South Australia. Energy & Mining. In situ recovery (ISR) mining. https://www.energymining.sa.gov.au/industry/minerals-and-mining/mining/major-projects-and-mining-activities/in-situ-recovery-ISR-mining. ↩︎

  6. Denison Mines Corp. Denison Announces 97% Recovery from Long-Term Phoenix ISR Core Leach Test; 2022. https://denisonmines.com/news/denison-announces-97-recovery-from-long-term-pho-122781/. ↩︎

  7. Gorman, G. O.; Michaelis, H. Von; Olson, G. J. Novel In-Situ Metal and Mineral Extraction Technology; Golden, Colorado, 2004. http://www.osti.gov/servlets/purl/835781-2V2h9D/native/. ↩︎