U-Pb zircon age and Pb isotopic constraints on the age and origin of porphyry and epithermal vein mineralization in the eastern Dawson Range, Yukon

Six dikes that are closely associated with the Klaza epithermal vein system in the Mt. Nansen district yield early Late Cretaceous U-Pb zircon ages (78.2-76.3 Ma); this age is similar to that obtained from the porphyry stock that hosts the Cyprus Cu-Mo-Au porphyry occurrence immediately to the southeast. These results support the interpretation that epithermal veins in the Mt. Nansen district are likely genetically related to subvolcanic magmatism. Granodiorite of the Dawson Range batholith that underlies most of the Klaza property gives a U-Pb zircon age of 107.9±0.3 Ma. These dates overlap with previously reported mid-Cretaceous U-Pb zircon ages for felsic dikes associated with the Brown-McDade and related vein and breccia deposits in the Mt. Nansen mine. The new results, together with regional dating and Pb isotopic data from western Yukon, emphasize the metallogenic importance of the “early Late Cretaceous” magmatic-hydrothermal event in this region.