GEOCHRONOLOGY OF CRETACEOUS PORPHYRY COPPER DEPOSITS OF THE COASTAL CORDILLERA OF NORTHERN CHILE (LATITUDES 26°30' TO 30°30' S)

21 new zircon U-Pb (LA-ICPMS-MC) and 12 mica 40Ar/39Ar ages for 8 Cu-Au porphyry deposits and prospects from the easternmost part of the Coastal Cordillera of northern Chile constrain the emplacement of porphyry-related magmas in this region from 108.5±3.4 to 88.2±1.7 Ma. Two groups of deposits occur, according to their respective radiometric ages; the older one with U-Pb ages from 108.5±3.4 to 99.8±0.5 Ma (latest Early Cretaceous) occurs between latitudes 28°30' and 30°30' S, and includes the Tricolor, Dos Amigos, Los Loros, and Andacollo deposits. This group includes the only two Cretaceous porphyry copper deposits currently exploited along the Coastal Cordillera of northern Chile (Andacollo and Dos Amigos). The younger group with U-Pb ages from 92.5±1.4 to 88.2±1.7 Ma (Late Cretaceous) occurs between latitudes 26°30' to 27°30' S, and includes the Dinamarquesa, Carmen, Porteña (Inca de Oro) and Los Toros porphyry prospects. These Cretaceous Cu-Au porphyries represent the earliest porphyry mineralization of the Chilean Andes, which developed during the waning stage of the arc-related Cretaceous magmatism along the current Coastal Cordillera. The older deposits (Tricolor, Dos Amigos, and Andacollo) occur along sinistral shear zones and appear to be formed during a stage of transpression, whereas the younger group appears to be originated during a phase of E-W compressive deformation that produced the inversion of the Early Cretaceous back-arc marine sedimentary basin in the region, preceding an eastward shift of the magmatic front. 11 new apatite fission track ages from 80 to 55 Ma indicate that exhumation cooling of these porphyries under the apatite closure temperature for fission track (105±20°C) took place from late Cretaceous to Paleogene; consistent with late Cretaceous surface uplift and later denudation of the area.