Fluid characteristics and evolution of porphyry Cu-Au-Mo and Mo systems, Yukon-British Columbia, Canada

Geochemical techniques (isotopic, major, trace, and rare earth elements, fluid inclusion, solute chemistry) have been used to investigate porphyry mineralization of the Canadian Cordillera. Specifically, the Endako porphyry Mo deposit, central British Columbia, and the Casino, Cash, and Mt. Nansen Cu-Au-Mo occurrences of the Yukon were studied with the objective of characterizing the hydrothermal fluids associated with alteration and mineralization and subsequently to produce a more comprehensive understanding of these systems. The crystalline rocks neighboring the porphyry occurrences in the Yukon were also studied with the objective of understanding their protoliths and tectonic setting during formation.;The low fluorine Endako porphyry Mo deposit is characterized by early quartz +/- molydenite stockwork veins, with K-feldspar-bearing selvages and paragenetically later quartz-molybdenite ribbon veins, with sericite-bearing selvages. Oxygen isotope, fluid inclusion and solute chemistry studies indicate the involvement of hydrothermal fluids, exsolved from a crystallizing melt, in the formation of the Endako molybdenum deposit. However, hydrogen isotope compositions suggest the early involvement of meteoric water in the ore forming fluids and ore genesis.;The geochemical characteristics of the Devonian-Mississippian rocks of west-central Yukon indicate that the Yukon was a land mass outboard of North America representing a continental arc during Devonian-Mississippian times. The mid-Cretaceous Dawson Range batholith represents magmas crustally derived of the Precambrian basement of the Yukon. Whereas, the late Cretaceous plutons, genetically related to porphyry Cu mineralization, are associated with magmas that were derived from a mantle source contemporaneous with subduction.;Biotites in granitic rocks altered by mineralizing fluids of the Casino occurrence possess elemental compositions distinct from biotites in neighboring unaltered granitic rocks. The observed chemical trends are similar to those reported from other porphyry Cu deposits; however, the absolute elemental contents are variable between porphyry Cu deposits. Calculated fugacity ratios of the hydrothermal fluids of porphyry Cu deposits suggest that log fH2O/fHCl and log fHF/ fHCl are similar; whereas, log fH2O/ fHF values are variable.;Isotopic compositions (H, Sr, Pb, Ar) of primary mineralizing fluids associated with porphyry Cu-Au-Mo mineralization of the west-central Yukon indicate that fluids are composed of mixed non-magmatic and magmatic fluids. This hypothesis is atypical to the generally accepted thinking of fluid origin of porphyry Cu systems.