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U-Pb, Re-Os, and 40Ar/39Ar geochronology of the Nambija Au-skarn and Pangui porphyry Cu deposits, Ecuador: implications for the Jurassic metallogenic belt of the Northern Andes

Chiaradia, Massimo ; Vallance, Jean ; Fontboté, Lluis ; Stein, Holly ; Schaltegger, Urs ; Coder, Joshua ; Richards, Jeremy ; Villeneuve, Mike ; Gendall, Ian

In: Mineralium Deposita, 2009, vol. 44, no. 4, p. 371-387

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    Title
    • U-Pb, Re-Os, and 40Ar/39Ar geochronology of the Nambija Au-skarn and Pangui porphyry Cu deposits, Ecuador: implications for the Jurassic metallogenic belt of the Northern Andes
    Author
    • Chiaradia, Massimo. Section des Sciences de la Terre, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Vallance, Jean. Section des Sciences de la Terre, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Fontboté, Lluis. Section des Sciences de la Terre, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Stein, Holly. AIRIE Program, Department of Geosciences, Colorado State University, 80523-1482, Fort Collins, CO, USA
    • Schaltegger, Urs. Section des Sciences de la Terre, University of Geneva, Rue des Maraîchers 13, 1205, Geneva, Switzerland
    • Coder, Joshua. Department Earth and Atmospheric Sciences, University of Alberta, T6G 2E3, Edmonton, Alberta, Canada
    • Richards, Jeremy. Department Earth and Atmospheric Sciences, University of Alberta, T6G 2E3, Edmonton, Alberta, Canada
    • Villeneuve, Mike. Geological Survey of Canada—Ottawa, 601 Booth Street, K1A 0E8, Ottawa, Ontario, Canada
    • Gendall, Ian. Chapleau Resources Ltd., Suite #104, 135-10th Avenue South, V1C 2NI, Cranbrook, BC, Canada
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:313923
    Summary
    New U-Pb, Re-Os, and 40Ar/39Ar dates are presented for magmatic and hydrothermal mineral phases in skarn- and porphyry-related ores from the Nambija and Pangui districts of the Subandean zone, southeastern Ecuador. Nambija has been one of the main gold-producing centers of Ecuador since the 1980s due to exceptionally high-grade ores (average 15g/t, but frequently up to 300g/t Au). Pangui is a recently discovered porphyry Cu-Mo district. The geology of the Subandean zone in southeastern Ecuador is dominated by the I-type, subduction-related, Jurassic Zamora batholith, which intrudes Triassic volcanosedimentary rocks. The Zamora batholith is in turn cut by porphyritic stocks, which are commonly associated with skarn formation and/or porphyry-style mineralization. High precision U-Pb and Re-Os ages for porphyritic stocks (U-Pb, zircon), associated prograde skarn (U-Pb, hydrothermal titanite), and retrograde stage skarn (Re-Os, molybdenite from veins postdating gold deposition) of the Nambija district are all indistinguishable from each other within error (145Ma) and indicate a Late Jurassic age for the gold mineralization. Previously, gold mineralization at Nambija was considered to be Early Tertiary based on K-Ar ages obtained on various hydrothermal minerals. The new Jurassic age for the Nambija district is slightly younger than the 40Ar/39Ar and Re-Os ages for magmatic-hydrothermal minerals from the Pangui district, which range between 157 and 152Ma. Mineralization at Nambija and Pangui is associated with porphyritic stocks that represent the last known episodes of a long-lived Jurassic arc magmatism (∼190 to 145Ma). A Jurassic age for mineralization at Nambija and Pangui suggests that the Northern Andean Jurassic metallogenic belt, which starts in Colombia at 3° N, extends down to 5° S in Ecuador. It also adds a new mineralization style (Au-skarn) to the metal endowment of this belt