Abstract

High-temperature, high-silica rhyolites are commonly found near Cu-Zn volcanic-associated massive sulfide (VMS) deposits in the Archean Abitibi subprovince. They are characterized by anhydrous phenocrysts (feldspar, quartz) in concentrations of generally <15 modal percent and have >73% SiO(2), high incompatible element contents, Rb/Sr > 1, Zr/Y < 5, La(N)/Yb(N) < 3.5, and negative Eu anomalies. They have zircon saturation temperatures of 840–940 ° C, as calculated by using the zircon solubility model, which are higher than most other Abitibi rhyolites. Considering their high zircon saturation temperatures, their composition, and their spatial and temporal associations with tholeiitic mafic and ultramafic rocks, Abitibi high-temperature rhyolites are similar to silicic volcanic rocks found in hotspot-related oceanic settings with anomalously high heat flow, such as in eastern Iceland. The association of high-temperature rhyolites with VMS deposits may provide a useful exploration guide where zircon inheritance is minimal, such as in many of the primitive Archean and Early Proterozoic greenstone belts.

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