Geology and Geochronology of the Golpu Porphyry and Wafi Epithermal Deposit, Morobe Province, Papua New Guinea

The Wafi-Golpu district of Papua New Guinea contains contrasting high- and intermediate-sulfidation styles of epithermal veins and alteration that have overprinted and partially obscured the giant, high-grade Golpu porphyry Cu-Au deposit. The initial stages of magmatic-hydrothermal activity produced high-grade porphyrystyle assemblages that are zoned about the Golpu diorite intrusions, with most mineralization formed between 8.76 ± 0.02 and 8.73 ± 0.01 Ma. Porphyry mineralization was followed by the eruption of the Wafi diatreme, after which upward-widening zones of epithermal alteration and mineralization have overprinted both the mineralized Golpu diorites and the Wafi diatreme. Above the top of the Golpu porphyry, vein and alteration assemblages include quartz (locally vuggy), alunite, pyrophyllite, kaolinite, dickite, and diaspore, with high-sulfidation mineralization consisting of pyrite-covellite-chalcocite-tennantite ± enargite ± bornite that transitions outward to a distal assemblage of disseminated pyrite-sphalerite ± tennantite. A zone of intermediate-sulfidation epithermal carbonate-sulfide ± quartz ± adularia veins and montmorillonite-chlorite ± muscovite ± illite alteration occurs along the margins of the high-sulfidation domain. Most of the epithermal Au occurs near the transition from the high- to intermediate-sulfidation domains. New geochronological results indicate that the main stage of Golpu porphyry mineralization to the last stage of Wafi epithermal veins lasted between 120 and 220 k.y.