Abstract: Porphyry to epithermal deposit models are inferred to best describe the Late Cretaceous Klaza Au-Ag-Pb-Zn-(Cu) deposit. Here we report evidence for a protracted and complex magmatic-hydrothermal system typical of porphyry-epithermal deposits (e.g., multiple magmatic events, magma mingling, relevant vein-alteration types). In the Klaza area, there are at least four compositionally and texturally distinct intrusions interpreted as part of the Casino intrusive suite (ca. 80–76 Ma) that intrude granodiorite country rock of the Whitehorse suite (ca. 105 Ma). A ca. 72 Ma dike swarm (likely Prospector Mountain suite) was emplaced approximately 4–5 m.y. after emplacement of the Casino suite. Evidence of high-T hydrothermal activity consists of early dark micaceous (EDM) veins, sinuous and planar A-type veins, B-type, and D-type veins, and molybdenite-quartz veins. Composite epithermal-type sulphide veins cut high-T Cu-Au-Mo mineralization associated with phyllic and lesser potassic alteration assemblages. The age of porphyry-type mineralization is constrained by 187Re-187Os molybdenite dating to ca. 77 Ma (Kelly) and ca. 71 Ma (Cyprus). The 40Ar-39Ar muscovite dates from phyllic alteration in the Central Klaza zone yield ages of ca. 77 Ma. These field observations, integrated with archival Cu-Au-assay data, suggest the Klaza epithermal veins are located in the phyllic alteration shell of a two-stage Cu-Au-Mo porphyry system. It is possible that the Klaza epithermal veins represent a Prospector Mountain-age porphyry–epithermal system overprinting a Casino-age porphyry system.

Authors: Lee, W.-S., Kontak, D.J. Richards, J.P. and Sack, P.

NTS Mapsheet(s): 115I03

Citation: Lee, W.-S., Kontak, D.J. Richards, J.P. and Sack, P. 2020. Updated geology and porphyry copper potential of the Klaza deposit, Mount Nansen district (Yukon MINFILE 115I 067). In: Yukon Exploration and Geology 2019, K.E. MacFarlane (ed.), Yukon Geological Survey, p. 75–97.

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