Geology and Mineral Zoning of the Los Pelambres Porphyry Copper Deposit, Chile
W. W. Atkinson, Alvaro Souviron, Thomas I. Vehrs, Alejandro Faunes G., 1998. "Geology and Mineral Zoning of the Los Pelambres Porphyry Copper Deposit, Chile", Andean Copper Deposits: New Discoveries, Mineralization, Styles and Metallogeny, Francisco Camus, Richard M. Sillitoe, Richard Petersen
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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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The copper deposits of Perú consist of porphyry Cu±Mo, Au, Ag, breccia pipe Cu-Mo, enargite vein and replacement Cu±Au, Ag, Zn, Pb, calcic skarn Cu±Fe, Au, Zn, amphibolitic skarn Cu±Fe, volcanogenic massive sulfide Cu-Zn, vein and manto Cu±Ag, Pb, Zn, Sn, W, and sandstone (“red bed”) Cu types. The vast majority of these deposits formed during the Andean Orogeny and are geographically and chronologically distributed in well-defined metallogenic domains. These domains correlate with geochemically distinct magmatic episodes.
The magmatic and metallogenic domains appear to be controlled in part by transverse growth-faults in the Mesozoic and older basement rocks underlying the intensely folded and thrust-faulted Mesozoic and Tertiary rocks of the higher structural levels of the Cordillera. During the Andean Orogeny the extent of magmatism and the corresponding metallogenic provinces were influenced by subducted plate segmentation and by continental margin basement tectonics. In addition, the lithologic nature of the host rocks played an important role in determining the types of copper deposits formed.
Porphyry Cu, breccia pipe Cu-Mo and calcic skarn Cu deposits are related to the Pomahuaca, Coastal and Caldera batholiths, as well as to felsic Cordilleran volcanism between 8° and 12°S. However, the largest and richest porphyry Cu deposits are related to the Caldera batholith. The Cobriza Cu-bearing skarn is the only significant copper deposit of pre-Mesozoic age.
Perú has many ore deposits associated with the Miocene felsic extrusive and intrusive rocks along the Cordillera, forming veins and disseminations in igneous rocks and noncarbonate sedimentary rocks, and replacement mantos, pipes and veins in limestones. Several are large and high-grade enargite-type deposits containing mainly Cu, Ag, Au, Pb and Zn, accompanied by significant amounts of Cd, Te, Se, In, Bi and Tl. Others are veins and mantos containing Cu±Ag, Pb, Zn, Sn, W.
The Mesozoic volcanosedimentary sequences along the coast host volcanogenic massive sulfide Cu-Zn and vein/manto-type amphibolitic skarn Cu±Fe deposits.
Red bed Cu deposits are relatively unimportant in Perú.
The following information on the history of copper mining in Perú has been condensed largely from Samame (1979), Petersen et al.(1990) and Benavides (1990).
In Perú, gold and silver were apparently used before copper. The latter was first mined and processed by the pre-Inca Chimú culture along the northern coast and by the Tiahuanaco civilization in the Lake Titicaca region.
Copper became an important metal during the Inca period,