7/29/2019 Ballard Et Al-02-CMP-Redox of From Ce in Zircons-Chile Norte 3

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The northern extent of the El Abra complex is definedby a sharp contact made with older Pajonal diorite(Dilles et al. 1997). Together, these comprise thePajonal-El Abra igneous suite. The El Abra complexconsists of quartz and biotite diorites (Dark and Centraldiorite), Equis monzodiorite, South granodiorite, ElAbra quartz monzonite porphyry, Apolo alkali biotiteleucogranite, aplite, and undifferentiated intrusive brec-cia (Graichen et al. 1995). Diorite and porphyry host the

bulk of the ore within the El Abra mine (Ambrus 1977;Maksaev et al. 1994), although the source of the copperhas not been proven.

Based on previous geological mapping, structuralreconstructions, and geochemical data (Graichen et al.1995; Dilles et al. 1997; Rosas 1999), the Los Picos-Fortuna and Pajonal-El Abra igneous suites are inter-preted to have formed part of a contiguous batholithprior to net sinistral displacement along the West Fault.Our recent zircon geochronology and geochemicalanalysis confirm this interpretation and indicate that this

composite body was emplaced over 5.5106 years be-tween 42.9 and 37.4 Ma (Ballard et al. 2003). In addi-tion, the zircon geochronology allows the emplacementsequence of the individual plutons of the Los Picos-Fortuna/Pajonal-El Abra complex to be established, and

shows that the compositionally evolved and ore-bearingEl Abra porphyry is the youngest unit. The spatial as-sociation of a significant copper deposit with theyoungest porphyry suggests a genetic link betweenmagmatic-hydrothermal mineralization and the finalstages of the magmatic evolution of this large igneouscomplex.

Other Eocene porphyry copper deposits

Immediately east of the Fortuna intrusive complex, thesuper-giant Chuquicamata copper deposit (Fig. 2) lies at

the southern end of the 14 by 2 km, north-south-trending Chuquicamata Igneous Complex (CIC; Zentilliet al. 1994; Tomlinson et al. 1995; Maksaev and Toml-inson 1995; Pardo and Rivera 1999). In the Chuquica-mata mine, the CIC consists of three intrusions, theEast, West and Bench porphyries, which can be distin-guished on the basis of texture and varying proportionsof plagioclase, quartz, orthoclase and biotite pheno-crysts (Aracena 1981). The Radomiro Tomic copperdeposit is located 7 km north of the Chuquicamata mine,also within the CIC (Cuadra et al. 1997). At Radomiro

Fig. 2 Geologic map of the Chuquicamata mine and surroundingarea (modified from Chong and Pardo 1994). Locations andidentities of samples are as follows: 1 and 2 Los Picos monzodi-orite, 3 Gris granodiorite, 4 Clara granodiorite, 5 San Lorenzorhyodacite porphyry, 6 leucocratic intrusive, 7 and 8 Opache mineporphyry, 9 Elena granodiorite, 10 Radomiro Tomic major facies

porphyry and 11 minor facies porphyry. Samples of East (12), West(13) and Bench (14) porphyries come from within the Chuquica-mata mine

Fig. 3 Geologic map of the El Abra area (modified fromTomlinson et al. 1995, and Graichen et al. 1995). Locations ofsamples are as follows: 1 Pajonal diorite, 2 Apolo leucogranite, 3Dark diorite, 4 Central diorite, 5 El Abra aplite, 6 Equismonzodiorite, 7South granodiorite, and 8 El Abra mine porphyry

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