Characteristics and timing of the Cu–Mo mineralization in the Kighal porphyry stock, NW Iran: Implications for the timing of porphyry Cu-related magmatism in Iran and southern Armenia

The quartz monzonite porphyry stock at Kighal in northwestern Iran intruded the Upper Eocene andesite to latite and basalt units, and the resulted hydrothermal activities led to the development of hydrothermal alteration zones, including potassic, phyllic, argillic and propylitic, coupled with Cu mineralization. Hypogene sulfide mineralization principally occurred within the potassic, transitional potassic–phyllic and phyllic alteration zones as disseminations, stockwork veinlets and open-space fillings. These hypogene minerals include pyrite, chalcopyrite and molybdenite, along with lesser amounts of sphalerite and galena at the marginal parts of the porphyry stock. By taking into account the development of hydrothermal alteration zones and their spatial distribution, stockwork-type mineralization of Cu–Mo minerals, and even the occurrence of mineralization zoning with Cu–Mo-rich ore within the stock and Cu–Pb–Zn ore in the marginal parts, mineralization at Kighal in association with the quartz monzonite sub-volcanic stock can be regarded as of porphyry copper type. However, its low Cu and Mo grade detracts its economic potential. Zircon U–Pb geochronology of the porphyry stock yielded Early Miocene ages of 20.0 ± 0.2 to 18.8 ± 0.2 Ma with a weighted mean of 19.24 ± 0.17 Ma, which correspond to the third porphyry Cu metallogenic epoch in NW Iran. The age data show that it is a little younger than the quartz monzonite porphyry stock in the Sungun porphyry copper deposit (PCD) and the porphyritic granodiorite stock in the Niaz prospect, while it is almost coeval with the porphyritic granodiorite stock in the Haft Cheshmeh PCD, as well as with the mineralization at the Masjed Daghi PCD in NW Iran. The Th/U ratios of the zircons range between 0.37 and 0.59, corresponding to the values for magmatic zircons. The analyzed zircons mainly possess initial εHf(t) values of 6.7 to 10.0, which suggest a juvenile and homogeneous magmatic source and the predominance of mantle-derived magmas with limited crustal assimilation.