The Future of the Southwestern North America Copper Industry

Despite 108 (+) years of large-scale copper production, there are still important advanced exploration and development projects in the region.  And, given the amount of post-mineral cover (gravel and volcanics) strewn over the Laramide arc, there are undoubtedly more deposits to be found. Challenges to exploration and development include the depth to the top of undiscovered deposits, the availability of mineral rights and water, with a rapidly growing population, advancing urbanization and increasing stress on the priority of other uses. For example, on the land use map shown in figure 17, black areas (e.g. Indian Reservations, National Parks, Military Reserves) are off limits and brown (mostly US Forest Service) are difficult. Mining can no longer take community support for granted, even in rural parts of the state, with opposition coming from across the political spectrum.

Figure 17. Land status in Arizona.

The Resolution project, discovered in 1995, Rosemont, discovered in the 60s, and Florence, discovered in the 70s, are currently featured regularly in headlines in Arizona (figure 18).

Figure 18. New copper projects in the industry queue as of July, 2019

The challenges facing Resolution, a deeply buried high-grade porphyry deposit just east of the historical Superior district being developed by a joint venture between Rio Tinto and BHP, are of both a technical and community relations nature. With the top of the deposit at 1700m depth, mining conditions are at the limits of current technology for larger-scale block caving, due to high rock and water temperatures and water volumes. As, or more, daunting are relations with the neighboring San Carlos Apache Tribe and their allies, who have made the fate of the Oak Flat Campground, bordering the NE side of the deposit and a traditional Native acorn gathering area, a cause celebre.

Exploitation of the Rosemont deposit, SE of Tucson, would be much simpler from a technical standpoint. it is an open pit/milling scenario using off-the-shelf technology. Here, opposition comes from more traditional foes: environmental groups and nearby private landowners. The former have latched onto the fate of the vanishingly small (and probably transient) jaguar population in the state as their rallying cry, while the latter run the gamut of NIMBY types, from retirees in Green Valley to well-heeled artists and vineyard owners in Sonoita.

Opposition to the Florence in-situ leaching project, due north off the eponymous community, has come from real estate developers, who see it as a threat (or perceived threat) to water quality in the subdivisions they are marketing on the southeast edge of Phoenix, which are creeping ever closer to the deposit. This sector is usually pro-growth (at any cost) and right-wing, but competition for water in the desert can turn even traditional allies against each other.

I suspect that two of these three projects will be developed in the long run, its just a question of how of a long that run is!

All operating open pit mines face the challenge of increasing stripping ratios as they are pushed deeper and deeper in pursuit of low-grade milling Cu-Mo sulfide ores. This is aggravated by the fact that the shallow leachable copper ores, which have offset at least some of the cost of that stripping, are being rapidly exhausted. Deeper mines also mean geotechnical challenges, in that slope stability of extremely high pit walls will be tested beyond what has ever been seen before.

In sum, favorable geology keeps on giving: Southwestern North America’s Laramide arc has low-grade primary Cu-Mo, as well as high-grade, oxidized and enriched deposits. These, together with mass mining and new recovery technology, made Arizona a major force in Cu mining from 1900s-1970s. A host of economic, social and political problems plagued mining starting in the late 1970s and led to its severely diminished importance, if not death. Implementation of SX-EW was a major factor in the resurrection of mining in late1980s-early 2000s. Relativity cheap power and high labor productivity have been key to the US copper mining industry staying competitive for last 20 years. SX-EW is becoming less important with time, simply because it is based on shallow oxidized and enriched ores, which are rapidly being exhausted. Low-grade but very large primary sulfide deposits with a significant Mo credit will be the predominant source of copper in the region in the future. While lots of exploration potential remains in covered areas, the key question is depth and its impact on economics. Other challenges include access to mineral rights, ever-extending timelines from discovery to production, the availability of water and community relations. In spite of these factors, exploration, discovery, development, and mining in Arizona and Southwestern North America can still be very rewarding!