Post-collisional magmatism and ore-forming systems in the Menderes massif: new constraints from the Miocene porphyry Mo–Cu Pınarbaşı system, Gediz–Kütahya, western Turkey

Abstract

The Pinarbasi Mo–Cu prospect is hosted within the Pinarbasi intrusion, which is exposed together with the NW–SE-trending Koyunoba, Egrigoz, and Baklan plutons along the northeastern border of the Menderes massif. The Pinarbasi intrusion predominantly comprises monzonite, porphyritic granite, and monzodiorite. All units of the Pinarbasi intrusion have sharp intrusive contacts with each other. The principal mineralization style at the Pinarbasi 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 Pinarbasi 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 Pinarbasi intrusion during back-arc magmatism. We conclude that the melt of the Pinarbasi 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 (∼18 Ma). The subsequent exhumation history of the Mo–Cu-bearing Pinarbasi intrusion is attributed to regional-scale uplift, and further exhumation along detachment faults of the associated core complexes during the middle to late Miocene.