See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/249057232 El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework Article in International Geology Review · January 1997 DOI: 10.1080/00206819709465258 CITATIONS READS 62 763 6 authors, including: Richard Tosdal Constantino Mpodozis Independent University of Chile 138 PUBLICATIONS 3,988 CITATIONS 144 PUBLICATIONS 8,137 CITATIONS SEE PROFILE SEE PROFILE Andrew James Tomlinson Christopher Mark Fanning El Servicio Nacional de Geología y Minería Australian National University 32 PUBLICATIONS 821 CITATIONS 573 PUBLICATIONS 25,836 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Tectonic evolution of the Andes View project Cartographie MCF View project All content following this page was uploaded by Richard Tosdal on 29 May 2014. The user has requested enhancement of the downloaded file. This article was downloaded by: [Canadian Research Knowledge Network] On: 28 May 2011 Access details: Access Details: [subscription number 932223628] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37- 41 Mortimer Street, London W1T 3JH, UK International Geology Review Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t902953900 El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework Paula Cornejoa; Richard M. Tosdalb; Constantino Mpodozisc; Andrew J. Tomlinsonc; Orlando Riverac; C. Mark Fanningd a Servicio National de Geologoia y Mineria, Santiago, Chile b U.S. Geological Survey, Menlo Park, California c Servicio National de Geologia y Mineria, Santiago, Chile d Australian National University, Canberra, Australia Online publication date: 06 July 2010 To cite this Article Cornejo, Paula , Tosdal, Richard M. , Mpodozis, Constantino , Tomlinson, Andrew J. , Rivera, Orlando and Fanning, C. Mark(1997) 'El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework', International Geology Review, 39: 1, 22 — 54 To link to this Article: DOI: 10.1080/00206819709465258 URL: http://dx.doi.org/10.1080/00206819709465258 PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. International Geology Review, Vol. 39, 1997, p. 22-54. Copyright © 1997 by V. H. Winston & Son, Inc. All rights reserved. El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework1 PAULA CORNEJO, Servicio National de Geologoía y Minería, Avenida Santa María 0104, Santiago, Chile RICHARD M. TOSDAL, U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 CONSTANTINO MPODOZIS, ANDREW J. TOMLINSON, ORLANDO RIVERA,2 Servicio National de Geología y Minería, Avenida Santa María 0104, Santiago, Chile AND C. MARK FANNING Australian National University, Canberra, Australia Abstract The Eocene (42 to 41 Ma) El Salvador porphyry copper deposit in the Indio Muerto district, northern Chile (26° 15' S Lat.), formerly thought to have formed at the culmination of a 9-m.y. period of episodic magmatism, is shown by new mapping, U-Pb and K-Ar geochronology, and petrologic data to have formed during the younger of two distinct but superposed magmatic events—a Paleocene (~63 to 58 Ma) and an Eocene (44 to 41 Ma) event. In the district, high-K Paleocene volcano-plutonic activity was characterized by a variety of eruptive styles and magmatic compositions, including a collapse caldera associated with explosive rhyolitic magma­ tism (El Salvador trap-door caldera), a post-collapse rhyolite dome field (Cerro Indio Muerto), and andesitic-trachyandesitic stratovolcanos (Kilometro Catorce-Los Amarillos sequence). Pre- caldera basement faults were reactivated during Paleocene volcanism as part of the collapse margin of the caldera. Beneath Cerro Indio Muerto, where the porphyry Cu deposit subsequently formed, the intersection of two major basement faults and the NNE-striking rotational axis of tilted ignimbrites of the Paleocene El Salvador caldera localized emplacement of post-collapse rhyolite domes and peripheral dikes and sills. Subsequent Eocene rhyolitic and granodioritic- dacitic porphyries intruded ~14 m.y. after cessation of Paleocene magmatism along the same NNE-striking structural belt through Cerro Indio Muerto as did the post-collapse Paleocene rhyolite domes. Eocene plutonism over a 3-m.y. period was contemporaneous with NW- SE-directed shortening associated with regional sinistral transpression along the Sierra Castillo fault, lying ~10 km to the east. Older Eocene rhyolitic porphyries in the Indio Muerto district were emplaced between 44 and 43 Ma, and have a small uneconomic Cu center associated with a porphyry at Old Camp. The oldest granodioritic-dacitic porphyries also were emplaced at ~44 to Downloaded By: [Canadian Research Knowledge Network] At: 21:38 28 May 2011 43 Ma, but their petrogenetic relation to the rhyolitic porphyries and younger granodioritic- dacitic porphyries in the district is unclear. The main porphyry Cu-Mo-related granodioritic- dacitic stocks in Quebrada Turquesa on Cerro Indio Muerto intruded, cooled, and were mineralized within ~1 m.y. between 42 and 41 Ma. Volumetrically minor late- to post-mineral porphyries are slightly more mafic than earlier granodioritic-dacitic porphyries, a compositional trend possibly repeated on several scales and more than once over the 3-million-year Eocene magmatic history of the Indio Muerto district. This compositional trend requires either addition of basaltic material into an open-system silicic magma chamber or tapping of progres­ sively deeper levels of a vertically zoned magma chamber. Eocene porphyry magmas were more hydrous and their residual source mineralogy richer in garnet than the relatively anhy­ drous Paleocene rocks, whose source was rich in pyroxene. The presence of inherited 1This paper is one of a series of contributions (Marcos Zentilli, compiler) to Project No. 342, Ages and Isotopes of South American Ores, of the International Geological Correlation Program. 2Present address: Pasaje Volcán San Francisco 3851, Peñalolén, Santiago, Chile. 0020-6814/97/240/22-33 $10.00 22 EL SALVADOR COPPER DEPOSIT REVISITED 23 zircons in Paleocene and Eocene rocks requires interaction with crustal rocks of Paleozoic and/ or Proterozoic age. Paleocene and Eocene igneous rocks in the Indio Muerto district were emplaced during distinct magmatic-tectonic events that are unrelated, although spatially associated. The district- scale Paleocene and Eocene eruptive styles and geochemical and mineralogic characteristics mimic characteristics of similar-aged igneous rocks throughout northern Chile (20°30' S Lat. to 27° S Lat.), attesting to the regional nature of the Paleocene and Eocene events. Porphyry Cu mineralization in the district furthermore is associated not only with an Eocene granodioritic- dacitic (42 to 41 Ma) complex, but also with one of an older Eocene (44 to 43 Ma) rhyolitic porphyry, implying that a long period of precursor magmatism is not required for generation of the El Salvador porphyry Cu-Mo deposit. Rather, the episodic magmatism preceding porphyry Cu mineralization reflects repeated structural localization through time of superimposed high- level volcano-plutonic complexes in an active magmatic arc. Introduction PORPHYRY COPPER SYSTEMS are frequently emplaced late in the magmatic history of vol­ cano-plutonic terranes, and many are believed to have formed in the roots of a coeval volcano (Titley and Beane, 1981; Sillitoe, 1973, 1988; Hedenquist and Lowenstern, 1994). This mag- mato-hydrothermal association has led to the obvious question of whether protracted precur­ sor magmatism, including volcanism, might play some role in the formation of porphyry copper systems (Titley, 1982; McCandless and Ruiz, 1993). The El Salvador copper deposit in the Indio Muerto district of northern Chile (Fig. 1), described in the seminal paper by Gustafson and Hunt (1975), is cited as one example where protracted magmatism preceded porphyry copper deposition (e.g., Titley and Beane, 1981; Sillitoe, 1988). Gustafson and Hunt (1975) concluded, on the basis of Rb-Sr and K-Ar geochronology, that the porphyry Cu- Mo deposit formed as the "culmination" of a Downloaded By: [Canadian Research Knowledge Network] At: 21:38 28 May 2011 ~9-m.y. period of episodic volcanic and sub- volcanic activity (Fig. 2), which began in the early Eocene at ~49 to 50 Ma with eruption of rhyolitic domes, was succeeded by the emplace­ FIG. 1. Distribution of porphyry Cu-Mo deposits