Geology, Mineralization, and Geochronological Constraints of the Mirador Cu-Au Porphyry District, Southeast Ecuador

摘要

The Mirador porphyry Cu-Au district is located in the southernmost sector of the northern Andean Cordillera, in Zamora-Chinchipe province, southeastern Ecuador. The district contains two significant porphyry Cu-Au Ag Mo deposits, Mirador and Mirador Norte, and an interconnected series of narrow, mineralized structures known collectively as Chancho. The principal mineralization in the porphyries is disseminated to blebby chalcopyrite developed primarily in potassic alteration, with overlying chalcocite supergene enrichment zones. Prior to radiometric dating presented in this study, these deposits were considered Late Jurassic based on close similarity, and therefore assumed age equivalence, with the well-dated Panantza, San Carlos, and Sutzu porphyry copper deposits located 40 km to the north. New U-Pb zircon ages confirm a Middle Jurassic age for granodiorite of the Zamora batholith at this location (163.8 1.9 Ma), and Late Jurassic ages for subvolcanic intrusions (156.2 1.0 and 153.1 1.3 Ma). Re-Os molybdenite ages average 156 1.0 Ma and indicate coeval mineralization between Mirador and Mirador Norte. Mineralization and related sub-volcanic igneous activity are closely associated at Mirador and represent the same temporal event recorded at Panantza-San Carlos and Sutzu, as well as coeval porphyry, skarn, and epithermal Au mineralization extending at least 80 km south, defining a north-south Cu-Au metallogenic belt spanning over 120 km.