In-situ recovery seeks to remove mineral ore from right where it sits, as opposed to removing large amounts of rock and earth above and around it. In-situ recovery is commonly used to recover copper and uranium.
In-situ recovery, or ISR, is an extraction process designed to leave a mine’s physical location undisturbed. It is touted as an environmentally cleaner method of extraction.
In a nutshell, in situ means “in the natural or original position,” and the process seeks to remove mineral ore from right where it sits, as opposed to removing large amounts of rock and earth above and around it (which, of course, is typically how mine sites operate).
ISR is commonly used to recover uranium. However, the process is also used to mine copper, and to extract deposits of water-soluble salts such as sodium chloride and sodium sulfate.
According to the Copper Development Association, ISR mines are comprised of injection wells and recovery wells that penetrate mineral-bearing rock. They’re built with acid-resistant casings and cemented from the top of the ore zone to the surface.
An acid or carbonate leach is pumped into porous ore through perforations in the well casings, dissolving the ore into the solution upon contact. The solution, now rich with copper or uranium ore, is then pumped through a series of recovery wells for processing. These wells surround the active leach area, preventing the leach solution from escaping and creating a flow to funnel the solution inward to the leaching zone.
Then, the ore-rich solution is transferred to a solvent extraction and electrowinning plant where an organic reagent is added to the solution to extract the mineral ore. After the ore is depleted of its mineral properties, the wells are sealed with cement and the land is returned to its original use.
Benefits of ISR
The ISR process has many benefits, the most notable of which is the cleanliness of the process itself. According to Excelsior Mining (TSXV:MIN), ISR removal is minimally invasive to the surrounding areas and to the mine itself. Since it doesn’t operate in the same way as a typical mine, it doesn’t create large amounts of waste or result in huge, unsightly open pits.
Elmer Stewart, CEO of Copper Fox Metals (TSXV:CUU), spoke with Copper Investing News about the benefits of the extraction method and noted the low costs associated with the process — since less equipment is required, the process utilizes less capital on the front end. The method also cuts down on potential hazards to employees due to accidents or contaminated dust inhalation, which can lead to additional heath issues.
Stewart also stated there is minimal noise involved with this method of extraction, allowing for better on-site communication and fewer disruptions for neighboring communities.
In-situ removal is relatively safe and well regulated, but risks still exist. There are rigid guidelines in place for ISR leaching, and the wells are coated to prevent any solution from escaping.
Additionally, for uranium operations, since the removal is underground from the ore’s natural resting place, most of the ore’s radioactivity remains underground as well, causing minimal release of radon and additional dust contaminants, according to the World Nuclear Association.
Furthermore, many guidelines require that following the end of a project’s life, the water in the area must be usable for the same purposes it was used for before the project’s construction. For that reason, local water will often undergo purification, commonly by reverse osmosis, following the closure of projects.
However, it is impossible to entirely remove all contaminants from water, which has caused concern over the ISR process and has led some to question whether the process is as safe as it is claimed to be.
According to the US Environmental Protection Agency, it is possible for the leaching solution to seep into groundwater. This has led to regulations and legislation requiring water treatment and testing.
Back in 2012, Ronnie Hawks, an environmental lawyer with Jennings, Haug & Cunningham, wrote a report for the Arizona Water Association in which he weighs the benefits as well as the risks of ISR leaching. The report states that the main risk is the potential spilling of the large amount of chemicals used in the process. Hawks adds that the solution targets more than the desired minerals, and the solution can be full of other contaminants and unwanted minerals as well.
However, proponents of the process argue that while risks exist, they still pose significantly less harm to the environment and human health than traditional methods of mining. This is especially true if the in-situ mine is not located near a residential area or where water is used for drinking.
Overall, due to the minimal invasiveness of the process, low overhead and reduced environmental impact, more and more mining companies have been turning to in-situ removal processes for various minerals. For example, the World Nuclear Association notes that 47 percent of the world’s uranium in 2013 was mined from in-situ operations.
Copper companies using ISR
Here is a brief look at some current copper projects that are using ISR:
- Excelsior Mining, Gunnison project — The Gunnison property, located 65 miles southeast of Tucson, Arizona, is 2,461 hectares in size. The project has measured and indicated mineral resources of 3.91 billion pounds. The annual production rate will be 110 million pounds of copper for the first 14 years, then declining for a 20-year mine life, with a total of 1.682 billion pounds of copper produced throughout the life of the mine.
- Copper Fox Metals, Van Dyke project — The Van Dyke project is a 1,100-acre oxide copper deposit located approximately 1.2 miles south of the Van Dyke oxide copper deposits in the Globe Miami mining district, approximately 90 miles east of Phoenix, Arizona. Using a 0.05 percent total copper cut off, the recently released inferred resource estimate for Van Dyke consists of 261.7 million tonnes grading 0.25 percent total copper containing 1.44 billion pounds of copper. Based on in-situ pressure leach tests, 89 percent of the copper contained in the samples is reported as soluble copper, both acid soluble and cyanide soluble.
- Taseko Mines (TSX:TKO), Florence project — Taskeo recently acquired Curis Resources to gain the Florence copper project, near Florence, Arizona. The project contains approximately 2.4 billion pounds of copper reserves with an average grade of 0.36 percent total copper, and the reserves are contained within a measured and indicated resource of 2.8 billion pounds of copper with an average grade of 0.33 percent total copper. A 2013 prefeasibility study reveals a pre-tax net present value of $727 million with an internal rate of return of 36 percent. Base-case study parameters include a $2.75 per pound long-term copper price and average copper recovery of 70 percent.