Geologic evolution of the Caylloma epithermal vein district, Southern Perú
Por:
Echavarria L., Nelson E., Humphrey J., Chavez J., Escobedo L., Iriondo A.
Publicada:
1 ene 2006
Resumen:
The silver- and base metal-rich Caylloma epithermal district in the Tertiary volcanic belt of southern Perú has been worked intermittently since the Incaic period and has produced over 100 million ounces (Moz) of Ag. Intermediate-sulfidation mineralization is present in veins hosted by Miocene andesitic volcanic and volcaniclastic rocks, with minor ore in underlying folded Jurassic sedimentary basement. New 40Ar/39Ar dates give a host rock age of 20.30 ± 0.11 Ma (andesitic volcanic matrix), a hydrothermal alteration age of 18.35 ± 0.17 Ma (adularia in vein wall rock), and postmineralization ages of 11.8 ± 0.8 and 12.25 ± 0.07 Ma (sanidine and biotite from a rhyolite dome). Gangue minerals include quartz, calcite, rhodonite, rhodochrosite, pyrite and minor adularia, illite, barite, and helvite. Ore minerals include sphalerite, galena, chalcopyrite, and tetrahedrite. Hydrothermal alteration is pervasive in lava flows but weak and localized near veins in volcaniclastic rocks. Hydrothermal alteration types include silicification (quartz-adularia and quartz-illite) and propylitization (chlorite + calcite ± illite). Banded veins show four stages of mineral precipitation: (1) early sugary quartz, chalcedony, pyrite; (2) manganese minerals; (3) quartz + sulfides; and (4) late calcite + quartz. Cyclic bands in the manganese stage (early sulfides, coarse- to medium-grained quartz, late rhodonite + calcite + chalcedony) are a few millimeters to 5 cm thick and form ore bands up to 1 m thick. Veins occupy dextral normal faults (020°-050°, 45°-70° SE) and extension fractures(060°-090°, 70°-90° SE) and are 1 to 25 m wide and as much as several kilometers long. The veins display complex and multiepisodic filling with textures characteristic of open-space precipitation such as crustiform banding, symmetric banding, vugs, breccias, and cockade and comb textures. We present a structural model in which the principal veins formed in subparallel northeast-striking dextral-normal faults and related extension fractures within a northwest-striking structural corridor bounded by sinistral regional faults; second- and third-order veins formed by bookshelf sliding related to movement on higher-order, dominantly strike-slip faults. Slickenlines have low rakes (20°-50° SW), and fault-kinematic analysis
Filiaciones:
Echavarria L.:
Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, United States
MHA, Granaderos 1363, Mendoza 5500, Argentina
Nelson E.:
Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, United States
Humphrey J.:
Department of Geology and Geological Engineering, Colorado School of Mines, Golden, CO 80401, United States
Chavez J.:
Mauricio Hochschild and Cia. Ltda., S.A.C., Pasaje El Carmen No. 180, El Vivero de Monterrico, Surco-Lima, Peru
Escobedo L.:
Mauricio Hochschild and Cia. Ltda., S.A.C., Pasaje El Carmen No. 180, El Vivero de Monterrico, Surco-Lima, Peru
Iriondo A.:
Department of Geological Sciences, Univesity of Colorado at Boulder, Boulder, CO 80309, United States
Centro de Geosciencias, Universidad Nacional Autónoma de México, Campus Juriquilla, 76230 Juriquilla, Querétaro, Mexico
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