Porphyry and High-Sulfidation Epithermal Mineralization in the Nevados Del Famatina Mining District, Argentina
A. J. Losada-CalderÓN, D. C. MCPhail, 1998. "Porphyry and High-Sulfidation Epithermal Mineralization in the Nevados Del Famatina Mining District, Argentina", Andean Copper Deposits: New Discoveries, Mineralization, Styles and Metallogeny, Francisco Camus, Richard M. Sillitoe, Richard Petersen
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This paper discusses the possible genetic relationship between two ore deposits in the Nevados del Famatina mining district, Argentina: Nevados del Famatina Cu-Mo-Au porphyry deposit and La Mejicana Cu-Au high-sulfidation epithermal deposit. The porphyry system crops out in three open annular areas dominated by porphyritic rocks at elevations between 4000 and 4800 m; the epithermal vein system is peripheral to the porphyry and crops out on adjacent ridges at elevations above 4500 m. The spatial, geologic, petrographic and geochronologic parameters suggest that there is a genetic relationship between the two deposits, and detailed mineralogic, fluid inclusion, and stable isotope studies and preliminary thermodynamic modeling provide additional support. The hydrothermal fluids, from which the ore, gangue, and alteration minerals were deposited, were dominated by magmatic volatiles, with admixture of groundwaters during the later vein stages in both the porphyry and epithermal deposits. Representative pressures, temperatures, and salinities decreased over the paragenetic stages of the porphyry and with increasing elevation in the late vein stages of the porphyry and epithermal systems. The fluids also became progressively more oxidized, more acidic, and lower in sulfur gas activity over the same stages and elevations. The temperature, pressure, and fluid composition (salinity, redox state, sulfur gas, acidity) inferred for the epithermal system are similar to those calculated for the last stage of the porphyry deposit. There are striking similarities in detailed mineralogy between the last porphyry vein stage and the epithermal veins. All available data support the hypothesis that the porphyry and high-sulfidation deposits are transitional and genetically related.
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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,