5 ESTIMATING ULTIMATE RESOURCES
5.4 Conclusions
It should be obvious from the previous sections, as well as the estimates and spec- ulations outlined in this section, that Earth contains a truly enormous amount of Cu. Just how much of this material might be mined now or in the future is not known, but it is definitely much larger than currently available estimates of reserves and resources. The long-term resource picture for most other mineral commodities, especially the metals, is probably similar. How long these might last depends not only on their supply, and our ability to find the deposits, but also on the rate at which we consume and recycle the commodities, plus on technological advances in mining and mineral processing as well as efficiencies of use and alternatives. These topics are far beyond the scope of this volume, but are obviously just as important.
For the moment, we hope we have demonstrated that mineral resources are much more abundant than simple reserve estimates indicate. It is our chal- lenge, as geoscientists, to find and help mine them. We trust that our picture of an evolving resources industry will encourage geochemists, and geoscientists in general, to think about and find ways to make significant contributions to the discovery, production and environmental challenges that the mining industry will face in the future. Below, we suggest a few of these challenges.
Box 5.3 – The Future of Open-pit Mining –Some environmental groups advocate a total ban on open pit mines. They applauded the remark made in 2016 by the incoming Philippines Environment and Natural Resources Secretary, in charge of mining, who proclaimed that open pit mining is “madness”. According to another group “In a bold and precedent-setting move, Costa Rica has prohibited all future open-pit metal mining! Environmentalists are celebrating the passage of the new law, which – approved unanimously by the Costa Rican Congress – establishes Costa Rica as a country that is ‘free from open-pit metal mining.’ Earthjustice and its partners are thrilled with this development …”. How realistic are these actions?
As mentioned in Section 4, many types of deposits can be exploited only by surface mines; for many others, an underground mine would cost so much more that the operation would not be viable. All of the world’s Al and half its Ni come from laterites that form as laterally extensive but relatively thin deposits at or close to the surface. Resources of these metals are sufficient to meet demand to well into the next century and, for all of this period, the deposits will be developed in open pit mines. When done properly, this type of operation has only a temporary impact on the environ- ment. The layer of topsoil at the surface is removed and conserved, and is replaced once the underlying ore has been removed. Examples of successful remediation can be found in regions south of Perth in Western Australia where the endemic jarrah forest is progressively restored after bauxite mining is completed (e.g., Gardner, 2001). Most other high-volume bulk commodities like Fe, Mn, aggregates, limestone (for cement) and industrial minerals (including gravel and sand) are mined in open pits. There are some exceptions, such as Kiruna in northern Sweden, a steeply dipping sheet-like Fe deposit that has been mined underground since the 1960s, but well over 90 % of Fe is recovered in vast open pits like those in the Hamersley region of Australia or the Carajás Mine in Brazil. Stringent procedures are now imposed to help assure the mine site is properly rehabilitated following mine closure, but total restoration of the large holes left after mining is impossible. The bottom line is that if modern society continues to consume Fe and steel for cars (electric or conventional), bridges and wind turbines, plus the rest of the infrastructure needed for the produc- tion of renewable energy, a large proportion of the raw materials will be recovered in open-pit mines, at least for several decades in the future.
For the base and precious metals, mining is and will continue to be divided between open pits and underground mines, depending on the nature of the deposit, its location, and other factors. There is a well-developed trend towards large-scale underground mining of Cu as the introduction of new and improved caving practices increase the efficiency of the process. Other factors that will favour underground mines are the exhaustion of near-surface deposits. Examples like the Mittersill tungsten mine in Austria illustrate the advantages of modern underground mines. The mine operates near a National Park and Nature Reserve but the operation is highly automated and the ore is transported to the ore-dressing plant through a 3-km long tunnel with the consequence that the mine is barely visible at the surface.
Finally, the development of in situ leaching techniques, whereby metals are extracted in fluids then transported to the surface, may eventually eliminate the need for tradi- tional mines.