Case Studies of 21st Century Exploration Success
The Nova-Bollinger deposit is a large nickel-copper sulfide deposit discovered in 2012 by a junior Australian exploration company, Sirius Resources. The deposit is interpreted to represent a magmatic sulfide accumulation within several stacked mafic sills that intruded a sequence of sedimentary rocks, which has been subsequently recrystallized and variably deformed by lower granulite facies metamorphism. The deposit is located in the Albany-Fraser orogen of Western Australia—a Proterozoic belt broadly similar to the Circum-Superior belt in North America, which hosts the Thompson and Raglan nickel mining camps. Although some previous explorers had recognized the similarity between these areas and also undertaken limited exploration for nickel, the prospectivity of the Albany-Fraser orogen for magmatic nickel deposits was largely unrecognized and the area was virtually unexplored prior to the involvement of Sirius.
The discovery is somewhat unusual because it is a blind, grassroots discovery made in what was previously assumed to be an unendowed geologic terrane by a small company with a small exploration budget. It is also unusual because the style of deposit discovered was exactly that which was originally targeted. The case study of the discovery includes the geologic concept, the exploration methods, and the key circumstances that led to the discovery of Nova-Bollinger. In one sense the discovery represents a textbook example of the deliberate and successful application of good geologic science and appropriate exploration methodology, but in another sense it was the culmination of numerous key decisions and seemingly unrelated events that spanned a period of nearly fifty years that created the necessary building blocks for the ultimate success. These building blocks include the involvement of a variety of other elements, including the efforts of previous mining companies, an accident by NASA, the persistence of a wealthy Australian prospector, and the initiative of the Government and Geological Survey of Western Australia.
In terms of process, the deposit was discovered by systematically using various methods that were tailored to the target style and the nature of the terrane, and also appropriate to the scale and stage of exploration. These comprised regional aeromagnetics for target definition, soil geochemistry for target verification and prioritization, shallow reconnaissance drilling for defining the source of soil anomalies, ground electromagnetic geophysics for defining discrete drill targets, and finally drilling. It is critical to also evaluate how information and misinformation can potentially affect the exploration process at every step, and how entirely extrinsic factors such as timing and luck can determine the outcome of the process. Of particular interest in the case of the Nova-Bollinger discovery is insight into how junior explorers operate compared to the bigger companies, what they have to do to be effective explorers, how they contribute to the overall well-being of the resources sector, and how their success is influenced by the degree to which three factors coincide—motive, means, and opportunity.
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).