Heap leaching is of course alive and well, and still pretty much centered on Nevada. The 2022 International Heap Leach Symposium, organized primarily by Dirk van Zyl, was held in Reno in September, and had an attendance of about 300 people split evenly between people working in gold and those working in copper. There seemed to be an interesting divergence between the two camps. The primary concern among the gold people was the physical and chemical behavior of the ore. The copper people were almost all presenting various instrumentation techniques for measuring solution flow within the heap.

The trends in the precious metals mining industry are not heading in the right direction as far as technical sophistication is concerned. If you measure the success of a heap leaching operation in terms of return-on-investment, there seem to be as many failures in 2022 (on a percentage basis) as there were when the industry was young, in the mid-1970s. The success rate was getting better in the mid-1980s, but now it is declining.

Why is this? It seems to be a result of two developments:

Firstly, while there are more projects today, the labor pool of practical hands-on university graduates is not keeping pace. For years, the mining industry has been saying that a severe labor shortage is coming. It is here. It is compounded a bit by the fact that young engineers have exciting alternatives, and the schools have responded by reducing the emphasis on learning hands-on applications expertise. The Mackay School of Earth Sciences and Engineering is responding a bit by creating a Center for Mining Excellence in Elko under the direction of Dr. Sam Spearing. One of its functions will be to work somewhat like a Community College, and train people who might want to fill the gap between being a technician and being an “academic” engineer.

Another reason we are seeing heap leach failures is that we are pushing the limits of what is possible. 10 years ago, it was possible to get equity financing in the Canadian markets for small high-grade projects that show good return-on-investment. Now, the emphasis seems to be on increasing the resource ounces even at the expense of having a decent return or a risk-free project. Of course, the large mining companies are getting larger and so they need orebodies with more contained resources. But that does not explain why small companies face a large hurdle for their small but very robust projects. Just like with the shortage of field engineers, there seems to be a shortage of young ambitious people in the financial community who are willing to spend the time to learn the industry and truly understand the risk-reward relationships. A few companies have been able to overcome this with good and engaged management, such as I-80 Gold, which has accumulated a group of exciting northern Nevada projects, Fortitude Gold with their very robust Isabella Pearl mine, and First Majestic Silver which developed a portfolio of small mines in Mexico and has now acquired Jerritt Canyon in Nevada.

Meanwhile, the copper industry has embraced heap leaching in a big way. Traditionally, they have had dump leaches, which are low-tech economic margin processes for recovering more copper than it costs. But now they are paying much more attention to investing in proper heap design and stacking methods. The gold industry is used to the chemistry being fairly straightforward, but in a copper heap leach, there are a lot of important variables such as pH, oxygen availability, and the health of the various bacteria, which are necessary to dissolve the copper minerals. There are a few true copper “heap leaches” in Arizona, but the majority of them are in South America.