Discovery and Geology of the Esquel Low-Sulfidation Epithermal Gold Deposit, Patagonia, Argentina
Richard H. Sillitoe, Chris Cooper, Marc J. Sale, Walter Soechting, Damian Echavarria, Jose Luis Gallardo, 2002. "Discovery and Geology of the Esquel Low-Sulfidation Epithermal Gold Deposit, Patagonia, Argentina", Integrated Methods for Discovery: Global Exploration in the Twenty-First Century, Richard J. Goldfarb, Richard L. Nielsen
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Esquel is a newly discovered vein gold deposit of low-sulfidation epithermal type situated on the eastern edge of the Patagonian Andes in southern Argentina. Some of the veins are prominently exposed in treeless country, but were not recognized until 1997. Drilling of >50,000 m has shown the deposit to contain 3.82 Moz of gold at an average grade of 6.11 g/t, all potentially amenable to open-pit extraction. The veins were formed during an interval of east-west extension and andesite-basaltic andesite and rhyolite dike emplacement at about 160 Ma, part of a prolonged episode of regional extension and bimodal volcanism throughout the Jurassic arc and back-arc provinces of Patagonia in both Argentina and Chile. The veins occupy a north-striking corridor transected by the main Galadriel-Julia vein, which occupies a remarkably strike-persistent tension gash. The Galadriel-Julia vein contains three closely spaced, shallowly pitching ore shoots over a strike distance of 2.4 km. East- and northeast-striking transfer zones exerted a major control on ore-shoot localization as well as on vein and related dike geometries. The tops of parts of several ore shoots are preserved beneath barren premineral volcanic host rocks, probably due to the protection afforded by concealment beneath oligocene volcanic rocks during Tertiary tectonic inversion, uplift, and erosion. This compressive event contributed to shearing of vein margins and other zones of contrasting ductility in the vein corridor. The veins comprise chalcedony, plus subsidiary quartz, pyrobitumen, calcite, adularia, and illite that display crustiform, cockade, and carbonate-replacement textures. Abundant dark-gray chalcedony is rich in pyrobitumen, a product of synhydrothermal pyrolysis of an underlying sequence of organic-rich black shale. Sulfides comprise <3 vol percent of vein filling and are dominated by pyrite, marcasite, and lesser arsenopyrite, which contribute <250 ppm each of Cu, Zn, and Pb. Native gold and electrum are associated with a variety of gangue and sulfide minerals, are rarely visible in hand sample, and contribute to an overall Ag/Au ratio of between 1 and 2. Discovery of the Esquel veins was a result of traditional prospecting, although the large size of the current gold resource owes much to conceptual geology backed up by drilling.
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Integrated Methods for Discovery: Global Exploration in the Twenty-First Century
The dominant forces that affect the mining industry in today's economy are globalization, entrepreneurship, and unprecedented minerals availability. The current malaise and diminished economic importance of the base and precious metal mining industry in the world economy are the result of ongoing, longterm trends. Shifting market forces within a changed geopolitical landscape have resulted in excess supplies and reduced demands for high-unit-value mineral products and for geologists and engineers in the exploration and mining industries. Although these changes are still evolving, professionals and the mining companies that employ them must realize that these changes are irreversible.
Mining has five dominant characteristics: (1) it is essential to society, (2) it is effective in keeping society supplied with abundant, low-cost mineral products, (3) historically, it has been wealth destructive for investors, (4) it has been subsidized, and (5) it is shaped by social and political forces. What is different now is that instead of being subsidized, the industry is being handicapped by governments and abandoned by investors. The industry has reacted to a marketing problem with an inappropriate strategy of cost reduction and increased production. The increased supply has resulted in decreased prices. Mining companies are earning low or negative rates of return.
Remedies for the larger mining companies and the high-unit-value metals businesses include: Exemplary behavior to regain the trust of the public, governments and investors; Continued consolidation to become sector leaders; Profit through value-added vertical integration and direct marketing to consumers Development of innovative consumer-based financing mechanisms, especially for exploration ventures Individuals and small groups that have been displaced from the mainstream must become entrepreneurs. They must engineer their own survival by shifting careers or by finding, developing, and capitalizing on exploration and production opportunities that are unrecognized by, or are too small for, the major companies.
The mining industry is here to stay. It is too necessary to society to be abandoned; however, the future size and shape of the industry will probably be unrecognizable to most of us. It will be leaner and more opportunistic. It will be characterized by entrepreneurial corporations of all sizes that dominate niches and sectors and that anticipate and profit from the changing needs of society