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El Indio Belt - El Indio, Tambo, Pascua Lama
Main commodities: Au Cu

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The El Indio Belt of Central Chile, some 500 km north of Santiago, and 180 km to the east of the coastal town of La Serena contains the three significant deposits, namely El Indio Au-Cu, and the Tambo and Pascua Lama Au orebodies. The El Indio-Tambo group of mines were nearing exhaustion in 2001 at the then current gold prices, and subsequently closed. Pascua-Lama was under development in 2005.

The host sequence at El Indio-Tambo comprises Oligocene to Miocene andesitic to rhyolitic tuffs and volcanics preserved in a fault bounded depression. The rhyolitic and dacitic host rocks have been strongly altered and bleached over considerable areas. Mineralisation in the belt is related to both an early porphyry type event at 12 to 10 Ma, and a later high sulphidation overprint at 7 to 6.5 Ma.

El Indio is a high sulphidation Au-Ag-Cu deposit hosted by welded ash flow tuffs that underlie andesitic volcanics in a north-south striking fault bounded depression. Mineralisation appears to be related to the emplacement of small felsic domes and is of late Miocene age. The ore is present as fault controlled veins covering an area of 500 x 150 m. Mineralisation was emplaced in two well defined phases, namely initial massive enargite-pyrite veins, and second stage quartz-gold veins. The massive sulphide veins are accompanied by kaolinite and lesser alunite alteration and are rich in Cu, but gold poor. The second stage has associated sericite and lesser pyrophyllite, with local bonanza gold grades. Total production plus reserves are quoted as 23.2 mt @ 6.6 g/t Au, 50 g/t Ag, 4% Cu. Past production of bonanza grade ore totalled 0.5 mt @ 121 g/t Au.

The Tambo mine is around 5 km to the south of El Indio, separated by Cerro Canto, an 800 m thick pile of altered dacitic tuffs with minor dacite and quartz porphyry intrusives, interpreted to be a volcanic feeder zone. A similar, but subsidiary centre, Cerro Elephante, is immediately to the east of Tambo. The three separate pits that constitute the Tambo 'mine' are characterised by 'higher level' barite-alunite vein and breccia ores. Grades in the three pits average around 7 g/t Au.

Pascua-Lama is some 50 km to the north of El Indio, on the Chile-Argentina border. Pascua is the section of the swarm of deposits in Chile, while Lama is in Argentina. At the end of 2004 it had a proven resource of 540 t (17.6 Moz) of contained gold comprising 370 Mt @ 1.50 g/t Au. The probable mineral resource comprised 44 Mt @ 1.96 g/t Au, accounting for another 86 t (2.6 Moz) Au. The operations are controlled by Barrick Gold Corp..
  Pascua-Lama is a structurally controlled high sulphidation acid sulphate system hosted by intrusive and volcanic rock sequences of Upper Paleozoic and Middle Tertiary age. Basement is predominantlycomposed of a multiphase granite pluton that may be a phase of the Permian Guanaco Sonso sequence of intrusives and volcanics. In the deposit area, the granite intrudes older diorites and volcanic pyroclastic units and is, in turn, intruded by diorite stocks and dykes of mid-Tertiary Bocatoma age. During the Tertiary, all of these rocks were cut by sub-vertical faulting and hydrothermal breccias were located at complex fault intersections.   Breccia bodies are found in the Esperanza, Quebrada de Pascua and Lama zones. The individual breccia zones range in size from from a few centimetres to greater than hundreds of metres across and typically correlate with the intersection of major structures. The large 'inter-mineral' breccia pipe Breccia Central, occurs in the Quebrada de Pascua area. At surface this breccia has dimensions of around 650 x 250 metres, while 200 to 400 m below surface the composite body tapers to approximately 550 x 130 m is known to at least 700 m below surface. This well-mineralised breccia pipe represents an explosive hydrothermal event related to the development of the Quebrada de Pascua ore deposit. The mineralised system is further cut by post-mineral breccias, the largest of which are Breccia Oeste and Breccia Sur. The north-south oriented Breccia Oeste pipe has surface dimensions of 500 x 150 m and extends to a depth of up to 300 m in the Esperanza area.

The most recent source geological information used to prepare this decription was dated: 2001.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

El Indio



  References & Additional Information
   Selected References:
Bissig T, Clark A H, Lee J K W, Hodgson C J  2002 - Miocene landscape evolution and geomorphologic controls on epithermal processes in the El Indio-Pascua Au-Ag-Cu Belt, Chile and Argentina: in    Econ. Geol.   v97 pp 971-996
Bissig T, Clark A H, Lee K W, et al.  2003 - Petrogenic and metallogenic responses to Miocene slab flattening: new constraints from the El Indio-Pascua Au-Ag-Cu belt, Chile/Argentina: in    Mineralium Deposita   v38 pp 844-862
Bissig, T., Clark, A.H., Rainbow, A. and Montgomery, A.,  2015 - Physiographic and tectonic settings of high-sulfidation epithermal gold-silver deposits of the Andes and their controls on mineralizing processes: in    Ore Geology Reviews   v.65, pp. 327-364.
Chouinard A, Williams-Jones A E, Leonardson R W, Hodgson C J, Silva P, Tellez C, Vega J and Rojas F  2005 - Geology and Genesis of the Multistage High-Sulfidation Epithermal Pascua Au-Ag-Cu Deposit, Chile and Argentina: in    Econ. Geol.   v100 pp 463-490
Davidson J, Mpodozis C  1991 - Regional geological setting of epithermal gold deposits, Chile: in    Econ. Geol.   v86 pp 1174-1186
Deyell C L, Bissig T, Rye R O,  2004 - Isotopic evidence for magamtic-dominated epithermal processes in the El Indio-Pascua Au-Cu-Ag belt and relationship to geomorphologic setting: in Sillitoe R H, Perello J and Vidal C E 2004 Andean Metallogeny: New Discoveries, Concepts and Updates Society of Economic Geologists, Denver,    SEG Special Publication 11 pp 55-73
Deyell C L, Leonardson R, Rye R O, Thompson J F H, Bissig T and Cooke D R  2005 - Alunite in the Pascua-Lama High-Sulfidation Deposit: Constraints on Alteration and Ore Deposition Using Stable Isotope Geochemistry: in    Econ. Geol.   v100 pp 131-148
Oyarzun R, Lillo J, Higueras P, Oyarzun J and Maturana H  2004 - Strong arsenic enrichment in sediments from the Elqui watershed, Northern Chile: industrial (gold mining at El Indio–Tambo district) vs. geologic processes : in    J. of Geochemical Exploration   v84 pp 53-64
Siddeley G, Araneda R  1999 - The El Indio - Tambo gold deposits, Chile: in   Proceedings of GOLD 86 Symposium, Toronto, 1986 Balkema, Amsterdam    pp 445-456
Sillitoe R H  1995 - Nevada, Chile: in Sillitoe R H,  Exploration and Discovery of Base- and Precious-Metal Deposits in the Circum-Pacific Region During the Last 25 Years Metal Mining Agency of Japan    pp 70-71
Sillitoe R H  1995 - El Indio, Chile: in Sillitoe R H,  Exploration and Discovery of Base- and Precious-Metal Deposits in the Circum-Pacific Region During the Last 25 Years Metal Mining Agency of Japan    pp 68-70
Sillitoe, R.H.,  1991 - Gold metallogeny of Chile - an introduction: in      Econ. Geol.   v.86, pp. 1187-1205.
Walthier N, Sirvas E, Araneda R  1985 - The El Indio gold, silver, copper deposit: in    E&MJ, Oct., 1985    pp 38-42

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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