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Discovery History of a Giant, High-Grade, Hypogene Porphyry Copper-Molybdenum Deposit at Los Sulfatos, Los Bronces-Río Blanco District, Central Chile

By
Vicente Irarrazaval
Vicente Irarrazaval
1
Anglo American Exploration Chile Limitada, Pedro de Valdivia 291, Piso 4, Providencia, Santiago, Chile
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Richard H. Sillitoe
Richard H. Sillitoe
2
27 West Hill Park, Highgate Village, London, N6 6ND, England
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Alan J. Wilson
Alan J. Wilson
1
Anglo American Exploration Chile Limitada, Pedro de Valdivia 291, Piso 4, Providencia, Santiago, Chile
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Juan Carlos Toro
Juan Carlos Toro
1
Anglo American Exploration Chile Limitada, Pedro de Valdivia 291, Piso 4, Providencia, Santiago, Chile
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William Robles
William Robles
1
Anglo American Exploration Chile Limitada, Pedro de Valdivia 291, Piso 4, Providencia, Santiago, Chile
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Graeme D. Lyall
Graeme D. Lyall
1
Anglo American Exploration Chile Limitada, Pedro de Valdivia 291, Piso 4, Providencia, Santiago, Chile
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Published:
January 01, 2010

Abstract

Los Bronces-Río Blanco copper-molybdenum district, located in the late Miocene to early Pliocene magmatic arc of central Chile, has been the focus of exploration and mining activities since the discovery of highgrade copper ore in 1864. From humble beginnings as a source of small tonnages of direct-shipping ore, the district has grown to be one of the world’s premier copper producers, with 2009 production exceeding 448,000 metric tons (t) of copper from open-pit and underground mines owned and operated by Anglo American (Los Bronces) and Codelco (Río Blanco).

Anglo American acquired Los Bronces in 2002 as part of its purchase of Compañía Minera Disputada de Las Condes from an Exxon Mobil Corporation affiliate. Near-mine exploration conducted by Anglo American Exploration Division since the acquisition resulted in addition of at least 65 million metric tons (Mt) of copper to the district mineral inventory in two world-class porphyry deposits, Los Sulfatos and San Enrique-Monolito.

Exploration activities at Los Sulfatos were undertaken by previous owners of Los Bronces in the late 1960s and early 1990s, but it was not until Anglo American’s third drilling campaign, in 2006 to 2007, that large volumes of high-grade, hypogene porphyry- and breccia-style mineralization with clear economic potential were discovered beneath a previously untested part of the prospect area. Copper-molybdenum mineralization at Los Sulfatos is related to at least two discrete porphyry centers and a large, composite magmatic-hydrothermal breccia complex. The current inferred mineral resource at Los Sulfatos is 1,200 Mt averaging 1.46 percent Cu and 0.02 percent Mo, although the overall potential is envisioned to be 4,000 to 5,000 Mt at 0.8 to 1.0 percent Cu.

Location of the deposit in precipitous high Cordilleran terrain, brevity of the summer field season, and rigorous environmental restrictions combined to complicate the exploration, and mandated helicopter support for the program. Key discovery tools at Los Sulfatos are considered to have been high-quality geologic mapping, innovative geologic thinking, and deep diamond drilling. Additional important factors include the early decision to appraise and rank all district prospects prior to commencement of exploration and to assign the program to Anglo American Exploration Division rather than to the Los Bronces mine geology team, thereby ensuring that timely evaluation of Los Sulfatos was conducted by personnel unencumbered with the daily responsibilities of an operating mine.

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Contents

Special Publications of the Society of Economic Geologists

The Challenge of Finding New Mineral Resources: Global Metallogeny, Innovative Exploration, and New Discoveries

Richard J. Goldfarb
Richard J. Goldfarb
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Erin E. Marsh
Erin E. Marsh
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Thomas Monecke
Thomas Monecke
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Society of Economic Geologists
Volume
15 (1)
ISBN electronic:
9781629490397
Publication date:
January 01, 2010

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