Finding the Copper Mine of the 21st Century: Conceptual Exploration Targeting for Hypothetical Copper Reserves
John P. Sykes, Allan Trench, 2014. "Finding the Copper Mine of the 21st Century: Conceptual Exploration Targeting for Hypothetical Copper Reserves", Building Exploration Capability for the 21st Century, Karen D. Kelley, Howard C. Golden
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An increasingly common perspective is that the predominant “copper mine of the 21st century” will be based on a large, low-grade deposit. Such a project will have to overcome “sustainable development” challenges and in turn may require higher copper prices than witnessed to date to achieve economic returns. Researchers therefore suggest that innovation and technological development in copper mining and processing are thus required to lower production costs. By contrast though, because much of the research assumes that new discoveries will be of lower quality than currently mined deposits, only a minimal role for copper exploration in the 21st century is anticipated, merely outlining further, ever lower quality copper resources. An alternate hypothesis is that the development problem is actually a discovery problem. The implication is that the exploration focus must change. Low-risk exploration during the recent copper price cycle has unveiled few new world-class copper deposits, thus the industry is largely now working with aged, suboptimal copper mine projects. As an illustration, sustainable development was only emerging as a concept when many of these projects were discovered, thus many are now proving problematic to advance toward mine status given current societal and environmental requirements. Exploration can help mitigate both resource depletion and sustainability problems, and the copper mine of 21st century may actually be a high-quality, but as yet undiscovered deposit, which can meet the twin goals of economic and sustainable development.
To discover high-quality sustainable and economic copper deposits, the exploration industry needs to build (or perhaps rebuild) its conceptual exploration capabilities. Three main conceptual challenges need to be addressed: (1) determining whether a copper deposit is likely to be economic from the earliest stages of exploration; (2) drawing sustainable development principles into the exploration targeting process; and (3) preparing for a future characterized by sudden, dramatic innovative technological changes that impact key elements of cost and uncertainty relating to the opening up of new exploration “search space” and other powerful external factors. To address these conceptual challenges and assist with exploration targeting, a number of new in-principle-only reserve types are introduced, including the following: (1) a “theoretical reserve” to aid understanding of the potential economics of a copper resource from the earliest stages of exploration; (2) a “conceptual reserve” incorporating sustainable development principles via the concept of “accessibility”; and (3) a “hypothetical reserve” representing undiscovered resources that have the potential to be both economic and accessible in the future.
Figures & Tables
Earth’s near-surface mineralogy has diversified over more than 4.5 b.y. from no more than a dozen preplanetary refractory mineral species (what have been referred to as “ur-minerals” by Hazen et al., 2008) to ~5,000 species (based on the list of minerals approved by the International Mineralogical Association; http://rruff.info/ima). This dramatic diversification is a consequence of three principal physical, chemical, and biological processes: (1) element selection and concentration (primarily through planetary differentiation and fluidrock interactions); (2) an expanded range of mineral-forming environments (including temperature, pressure, redox, and activities of volatile species); and (3) the influence of the biosphere. Earth’s history can be divided into three eras and ten stages of “mineral evolution” (Table 1; Hazen et al., 2008), each of which has seen significant changes in the planet’s near-surface mineralogy, including increases in the number of mineral species; shifts in the distribution of those species; systematic changes in major, minor, and trace element and isotopic compositions of minerals; and the appearance of new mineral grain sizes, textures, and/or morphologies. Initial treatments of mineral evolution, first in Russia (e.g., Zhabin, 1979; Yushkin, 1982) and subsequently in greater detail by our group (Hazen et al., 2008, 2009, 2011, 2013a, b; Hazen and Ferry, 2010; Hazen, 2013), focused on key events in Earth history. The 10 stages we suggested are Earth’s accretion and differentiation (stages 1, 2, and 3), petrologic innovations (e.g., the stage 4 initiation of granite magmatism), modes of tectonism (stage 5 and the commencement of plate tectonics), biological transitions (origins of life, oxygenic photosynthesis, and the terrestrial biosphere in stages 6, 7, and 10, respectively), and associated environmental changes in oceans and atmosphere (stage 8 “intermediate ocean” and stage 9 “snowball/hothouse Earth” episodes). These 10 stages of mineral evolution provide a useful conceptual framework for considering Earth’s changing mineralogy through time, and episodes of metallization are often associated with specific stages of mineral evolution (Table 1). For example, the formation of complex pegmatites with Be, Li, Cs, and Sn mineralization could not have occurred prior to stage 4 granitization. Similarly, the appearance of large-scale volcanogenic sulfide deposits may postdate the initiation of modern-style subduction (stage 5). The origins and evolution of life also played central roles; for example, redox-mediated ore deposits of elements such as U, Mo, and Cu occurred only after the Great Oxidation Event (stage 7), and major Hg deposition is associated with the rise of the terrestrial biosphere (stage 10; Hazen et al., 2012).