Post-Collisional Magmatism and Ore-Forming Systems in the Menderes Massif: New Constraints from the Miocene Porphyry Mo-Cu Pa +/- Narbaaya +/- System, Gediz-Kutahya, Western Turkey

Abstract

The PA +/- narbaAYA +/- Mo-Cu prospect is hosted within the PA +/- narbaAYA +/- intrusion, which is exposed together with the NW-SE-trending Koyunoba, Egrigoz, and Baklan plutons along the northeastern border of the Menderes massif. The PA +/- narbaAYA +/- intrusion predominantly comprises monzonite, porphyritic granite, and monzodiorite. All units of the PA +/- narbaAYA +/- intrusion have sharp intrusive contacts with each other. The principal mineralization style at the PA +/- narbaAYA +/- prospect is a porphyry-type Mo-Cu mineralization hosted predominantly by monzonite and porphyritic granite. The porphyry type Mo-Cu mineralization consists mostly of stockwork and NE- and EW-striking sub-vertical quartz veins. Stockwork-type quartz veins hosted by the upper parts of the porphyritic granite within the monzonite, are typically enriched in chalcopyrite, molybdenite, pyrite, and limonite. The late NE- and EW-striking normal faults cut the stockwork vein system and control the quartz-molybdenite-chalcopyrite-sphalerite-fahlore-galena veins, as well as molybdenite-hematite-bearing silicified zones. Lithogeochemical and whole-rock radiogenic isotope data (Sr, Nd and Pb) of the host rocks, together with Re-Os molybdenite ages (18.3 +/- 0.1 Ma - 18.2 +/- 0.1 Ma) reveal that the monzonitic and granitic rocks of the PA +/- narbaAYA +/- intrusion were derived from an enriched lithospheric mantle-lower crust during Oligo-Miocene post-collisional magmatism. The lithospheric mantle was metasomatised by fluids and subducted sediments, and the mantle-derived melts interacted with lower crust at 35-40 km depth. This mechanism explains the Mo and Cu enrichments of the PA +/- narbaAYA +/- intrusion during back-arc magmatism. We conclude that the melt of the PA +/- narbaAYA +/- intrusion could have rapidly ascended to mid-crustal levels, with only limited crustal assimilation along major trans-lithospheric faults as a result of thinning of the middle to upper crust during regional extension, and resulted in the development of porphyry-style mineralization during the early Miocene (similar to 18 Ma). The subsequent exhumation history of the Mo-Cu-bearing PA +/- narbaAYA +/- intrusion is attributed to regional-scale uplift, and further exhumation along detachment faults of the associated core complexes during the middle to late Miocene.