Abstract

The Kighal porphyry Cu deposit, in the Arasbaran magmatic belt (AMB), is hosted by Late Eocene to Oligocene volcanic rocks and Miocene high–K calc–alkaline subvolcanic intrusions. The Miocene quartz monzonite stocks host porphyry–style Cu mineralization characterized by potassic, phyllic, argillic, and propylitic alteration zones and an advanced argillic lithocap. The Ar–Ar dating of secondary biotite from the potassic alteration and alunite from the lithocap yields precise ages of 20.10 ± 0.18 Ma and 19.15 ± 0.21 Ma, respectively, documenting the evolution of the hydrothermal system over ~ 1 Myr. Hydrothermal rutile occurs in the deposit from the proximal potassic to distal propylitic alteration zones, and their Ti–Fe–Cr–V–W contents can be used as a fertility indicator which suggests a decrease from the proximal zones towards the distal zones. The geochemical fingerprints of the Kighal (and in general the AMB) igneous rocks reflect a post–collisional arc setting. Their distinctly high Th/Yb and Ta/Yb ratios are typical of high–K calc–alkaline intrusions, suggesting that their parental melts were derived from an enriched upper mantle source modified by slab–derived components. Their 87Sr/86Sr(i) (0.70427 to 0.70452) and 143Nd/144Nd(i) (0.512712 to 0.512754) ratios reveal that the magmas experienced moderate crustal assimilation during their magmatic evolution, also supported by increasing Th/La and 87Sr/86Sr(i) and decreasing εNd(i) values with increasing SiO2 content. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of the intrusions (18.67 to 18.84, 15.60 to 15.66, and 38.83 to 39.06, respectively) reveal a crustal origin. Hence, a post–collisional arc setting is proposed for NW Iran, in which mantle–derived mafic melts underwent a MASH process and ascended into shallow magma chambers in the upper crust associated with moderate crustal contamination, which account for the formation of large–scale porphyry Cu mineralization in the AMB.