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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 66 (1982)

Issue: 7. (July)

First Page: 986

Last Page: 987

Title: New Gold-Silver-Copper Orebody at El Indio, Chile: ABSTRACT

Author(s): Thomas N. Walthier, Juan A. Proano, Ramon Araneda, Jack Crawford

Article Type: Meeting abstract

Abstract:

In June 1975, a St. Joe Minerals Corp. geologist, Dave Thomson, visited a remote prospect called El Indio, 300 mi (500 km) north of Santiago, close to the Argentine frontier at 13,000 ft (4,000 m) elevation. He recognized the great potential and St. Joe moved promptly. However, an agreement to purchase 80% of the property was not signed until June 30, 1976. Intensive exploration and development followed. It took another year to negotiate a foreign investment agreement with the government of Chile.

On December 2, 1981, the El Indio mine-mill complex was dedicated. The total investment approximates U.S. $200 million and the facility will process 1,380 tons (1,250 MT) ore per day. Mill-feed ore reserves at the time of dedication were calculated at 3.1 million tons averaging 12 g gold, 144 g silver, and 3.5% copper. In addition, direct shipping high-grade ore reserves are estimated at 70,000 tons averaging 11 oz (345 g) of gold per ton. Similar material has been mined and shipped since 1979, containing in excess of 345,000 oz (10,750 kg) of gold. Our geological assessment is that continued exploration at El Indio will discover considerably more ore of both types.

The ore is found in a complex vein system within volcanic andesites, dacites, and quartz dacites within, but near the border

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of, a caldera. The regional structural pattern is north-south faulting. Northeast cross faults forming sigmoid loops are very important ore controls.

Massive enargite-pyrite veins are up to 33 ft (10 m) wide. Propylitic, argillic, quartz-sericite, and siliceous alteration are widespread, with precious metal content favoring the highly siliceous areas. Gold is rarely visible as average grain size of the native metal is 5 microns.

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