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Geology and Mineral Zoning of the Los Pelambres Porphyry Copper Deposit, Chile

By
W. W. Atkinson
W. W. Atkinson
Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309, U.S.A.
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Alvaro Souviron
Alvaro Souviron
4850 South Ammons Street, #937, Littleton, Colorado 80123, U.S.A.
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Thomas I. Vehrs
Thomas I. Vehrs
Cyprus Minerals Company, Casilla 126 - Correo 35, Santiago, Chile
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Alejandro Faunes G.
Alejandro Faunes G.
Compañía Minera Los Pelambres, Alameda 1146, 4° Piso, Sector B, Santiago, Chile
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Published:
January 01, 1998

Abstract

Los Pelambres, located 200 km north of Santiago, Chile, is a major porphyry copper deposit within a small intrusive complex hosted by Early Cretaceous andesitic lavas. The complex consists of a preore tonalite stock which was intruded by a series of porphyries, ranging from quartz diorite to quartz monzonite. K-Ar dates cannot discriminate ages of the individual units, which yielded an average age of 9.9 ± 1.0 Ma. Hypogene mineralization was introduced with quartz stockwork veining, potassic alteration, and breccia pipes. The entire complex was subjected to pervasive biotitization of hornblende. The stockworks show a sequence of types, including Granular Quartz veins lacking obvious alteration halos, quartz veins with K-feldspar halos, and Green Mica veins consisting principally of biotite and phengite. The main stage of mineralization consists of quartz veins with complex alteration halos containing quartz, K-feldspar, biotite, andalusite, and, less commonly, corundum. All these types of veins and alteration contain anhydrite, chalcopyrite, and bornite. Magnetite is present locally in the mica veins and alteration. A later stage of Comb Quartz veins introduced most of the molybdenum, with only minor K-feldspar and sericitic alteration. Late veins contain pyrite and quartz and have sericitic envelopes. Breccia pipes, up to 600 m across, have matrices of igneous rocks, biotite, K-feldspar, quartz, tourmaline, magnetite, chalcopyrite, bornite, pyrite, and molybdenite. Supergene enrichment produced 560 million tonnes of enriched ore with a grade of 0.93 wt. percent Cu. Sulfide minerals occupy a bornite-chalcopyrite zone at the center of the deposit, surrounded by a pyrite-chalcopyrite zone, with increasing pyrite outward related to the sericitic alteration. Molybdenum occupies a truncated dome-shaped zone near the center of the bornite-chalcopyrite zone, which is also the location of the largest breccia pipe. Metal reserves are in excess of 3,300 million tonnes with a grade of 0.63 wt. percent Cu, 0.016 wt. percent Mo, using a 0.4 wt. percent Cu cutoff

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Contents

Special Publications of the Society of Economic Geologists

Andean Copper Deposits: New Discoveries, Mineralization, Styles and Metallogeny

Francisco Camus
Francisco Camus
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Richard M. Sillitoe
Richard M. Sillitoe
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Richard Petersen
Richard Petersen
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Society of Economic Geologists
Volume
5
ISBN electronic:
9781629490298
Publication date:
January 01, 1998

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