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Discovery and Geology of the Esquel Low-Sulfidation Epithermal Gold Deposit, Patagonia, Argentina

By
Richard H. Sillitoe
Richard H. Sillitoe
27 West Hill Park, Highgate Village, London N6 6ND, England
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Chris Cooper
Chris Cooper
Galloway Mineral Services, Hartburn, Kirkcudbright DG6 4XS, Scotland
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Marc J. Sale
Marc J. Sale
‘Oape’, Strath Oykel, Sutherland IV24 3DP, Scotland
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Walter Soechting
Walter Soechting
Minera El Desquite S. A., 9 de Julio 451, 9200 Esquel, Chubut, Argentina
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Damian Echavarria
Damian Echavarria
Minera El Desquite S. A., 9 de Julio 451, 9200 Esquel, Chubut, Argentina
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Jose Luis Gallardo
Jose Luis Gallardo
Minera El Desquite S. A., 9 de Julio 451, 9200 Esquel, Chubut, Argentina
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Published:
January 01, 2002

Abstract

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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Special Publications of the Society of Economic Geologists

Integrated Methods for Discovery: Global Exploration in the Twenty-First Century

Richard J. Goldfarb
Richard J. Goldfarb
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Richard L. Nielsen
Richard L. Nielsen
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Society of Economic Geologists
Volume
9
ISBN electronic:
9781629490335
Publication date:
January 01, 2002

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