Trace-element distribution in cassiterite and sulfides from rubané and massive ores of the Corvo deposit, Portugal

A large number of samples containing sulfides, sulfosalts and cassiterite from the Corvo volcanogenic massive sulfide deposit, exploited at the Neves-Corvo mine, southern Portugal, were analyzed using electron and proton microprobes after a detailed examination by reflected-light ore microscopy. The samples are representative of the main four types of ore: cupriferous rubane ore, rubane ore with tin, cupriferous massive sulfide ore and cupriferous massive sulfide ore with tin. The trace-element distribution among the minerals from the four ores, and particularly the high Sri and In contents as well as the Se/S values of pyrite, provide evidence of a magmatic signature for this complex and unique deposit. With respect to cassiterite, which is a characteristic major ore mineral at the Corvo deposit, both chemical composition and textural relationships to sulfides suggest that the high-temperature reduced fluids that deposited sulfides also deposited cassiterite. The mineralogical and geochemical data support the field hypothesis of an allochthonous origin for rubane ores, inferred to be a part of the stockwork of massive mineralization, thrust on the top of massive ores during the Late Hercynian.