Oxidized sulfur-rich arc magmas formed porphyry Cu deposits by 1.88 Ga

Abstract Most known porphyry Cu deposits formed in the Phanerozoic and are exclusively associated with moderately oxidized, sulfur-rich, hydrous arc-related magmas derived from partial melting of asthenospheric mantle metasomatized by slab-derived fluids. Yet, whether similar metallogenic processes also operated Precambrian remains obscure. Here we address issue investigating origin, f O 2 , S contents calc-alkaline plutonic rocks Haib deposit Paleoproterozoic Richtersveld Magmatic Arc (southern Namibia), an interpreted mature island-arc setting. We show that ca. 1886–1881 Ma ore-forming magmas, originated a mantle-dominated source minor crustal contributions, were relatively oxidized (1?2 log units above fayalite-magnetite-quartz redox buffer) sulfur-rich. These results indicate sulfur-rich arc magma mineralization already existed late Paleoproterozoic, probably as result recycling sulfate-rich seawater or sediments subducted oceanic lithosphere at time.