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1 Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET).
2 Centro Patagónico de Estudios Metalogenéticos, CIMAR, Facultad de Ingeniería, Universidad Nacional del Comahue, Av. Buenos Aires 1400 (8300) Neuquén, Argentina.
3 Instituto de Recursos Minerales, Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata, Calle 64 N° 3, 1900, La Plata, Argentina.
4 Centro da Desenvolvimento de Tecnología Nuclear (CDTN-CNEN), Belo Horizonte, MG, Brazil.
5 Department of Geology, Smith College, Northampton, MA 01063, United States.
Correspondence: Corresponding Author: mfranchi{at}uncoma.edu.ar
Several Fe, Fe-Cu, and Cu-Ag prospects hosted by Mesozoic carbonate-rich sedimentary rocks that were intruded by diorite stocks define an approximately 20 x 200 km belt along the Andes Cordillera of southwest Mendoza province, Argentina (34°–36°S). This belt includes the Hierro Indio and Vegas Peladas Fe skarns, Las Choicas, and several other Cu-(Ag) prospects.
The main features of the Fe skarns include: association with mantle-derived middle Miocene (~15–11 Ma) diorite stocks and sills; widespread alteration including epidote ± amphibole ± magnetite endoskarns, and zoned garnet (Grs0–66 Adr32.5–100) ± magnetite ± pyroxene (Di24–50 Jo2–9 Hd74–41) exoskarns formed from oxidized, saline, high-temperature brines (530°–660°C; 60–70 wt.% NaCl equiv.); and magnetite-hematite orebodies associated with quartz ± epidote ± calcite ± actinolite formed at lower temperatures (290°–436°C) from saline fluids (32–50 wt.% NaCl equiv.) of magmatic origin.
West of the Fe skarn belt, the Valle Hermoso district covers more than 300 km2 and hosts several poorly known Cu-(Ag) prospects (estimated 30 Mt with 1.5% Cu and 20 g/t Ag). These prospects share many characteristics with the iron oxide copper-gold-type systems and manto-type Cu deposits of northern and central Chile. One of the prospects (Las Choicas) is located at the apex of a regional 015°-trending anticline, along the contact of stratified calcareous sandstone and limestone (Neocallovian-Oxfordian) with a diorite pluton. This pluton has positive Ta and Nb anomalies (on normalized diagrams) and a high Ti content, features uncommon in Miocene diorites associated with Fe skarns and of magmas derived from sub-arc mantle sources. Alteration at Las Choicas includes early widespread chlorite + calcite ± albite ± scapolite ± ilmenite or titanite ± apatite, and local actinolite ± hematite ± biotite alteration of diorite and sedimentary rocks along contacts. Later Cu mineralization (1%–10% Cu) is associated with calcite ± albite ± quartz alteration in fractures, vein networks, and crackle breccias. Mineralization is zoned from bornite ± chalcopyrite ± millerite with Zn, As, Mo, Ag, and U anomalies in the main orebody, through chalcopyrite-rich breccias with Zn anomalies, and chalcopyrite ± tetrahedrite vein networks with Sb, As, Ag, and Zn anomalies in the uppermost zone, to a Cu-depleted pyrite-rich envelope with Co anomalies, and finally to late, barren calcite veins in distal zones.
Key Words: Fe skarns • manto Cu deposits • IOCG deposits • late Miocene • calc-alkaline diorite plutons • Cordillera Principal • southwest Mendoza
This article has been cited by other articles:
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  J. M. Pons, M. Franchini, L. Meinert, C. Recio, and R. Etcheverry Iron Skarns of the Vegas Peladas District, Mendoza, Argentina Economic Geology, March 1, 2009; 104(2): 157 - 184. [Abstract] [Full Text] [PDF]
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