Cretaceous molybdenite in metasomatic epidosite associated with the Pounamu ophiolite, New Zealand

Epidosites occur in association with pelagic and quartzofeldspathic metasediments overlying the Pounamu suprasubduction zone ophiolite. They are dominated by epidote with minor diopside, tremolite, titanite, zircon and quartz. Detrital zircon age spectra are similar to those of associated quartzofeldspathic schist, with minimum ages of Cretaceous (c. 106 Ma). Epidosite was derived by metasomatic replacement of this metasedimentary protolith by Ca-rich fluids, likely derived from the underlying ophiolite. One epidosite contains laminae and veinlets of molybdenite, which yields a Re/Os age of c. 89.7 ± 0.6 Ma. Metasomatic formation of epidosite and molybdenite mineralisation occurred during the interval between c. 106 and c. 70 Ma when the Pounamu terrane component of the Alpine Schist underwent accretion, subduction, hydrothermal alteration, mineralisation and metamorphic recrystallization. Molybdenite occurrence is unique in the context of Haast Schist metallogenesis, with Mo most likely derived by leaching and redistribution from the sedimentary cover of the Pounamu ophiolite.