Abstract

—The Kighal porphyry Cu–Mo deposit, located at 46°42′36″ N and 38°37′06″ E, occurs 120 km north of Tabriz and 12 km north of Varzeghan in the Arasbaran magmatic belt, NW Iran. The geologic units in the Kighal area are Eocene and Oligocene volcanic rocks associated with Miocene intrusive and subvolcanic rocks. Quartz-monzonite porphyry in the Kighal area hosts porphyry style Cu–Mo mineralization consisting of four alteration zones (potassic, phyllic, argillic, and propylitic) and abundant quartz veinlets. Based on mineralogy and geochemistry data, the intrusive and subvolcanic rocks belong to quartz-diorite, diorite, and granite units with high-K calc-alkaline to calc-alkaline affinities. All samples are enriched in LILE and depleted in HFSE, pointing to a mantle magma source contamination with subducted oceanic-crust material. Three types of fluid inclusions are identified in quartz from different quartz-sulfide veinlets, including multiphase (LVS) and liquid-rich (LV) inclusions in the potassic zone, liquid-rich (LV) and vapor-rich (VL) inclusions in the phyllic zone, and liquid-rich (LV) inclusions in the silicic zone. Microthermometry studies showed that Th in multiphase fluid inclusions in the potassic zone varied from 265 to 450 °C and salinity, from 38 to 59 wt.% NaCl-equiv. These values are higher than those of two-phase fluid inclusions in the phyllic zone (Th of 163 to 466 °C and salinity of 0.3 to 11 wt.% NaCl-equiv.). The calculated δ18OH2O and δDH2O values in biotite, sericite, and quartz from potassic, phyllic, and silicic zones showed that it is predominantly magmatic water with a lesser amount of meteoric water that is responsible for mineralization in the potassic zone. Light δDH2O values of biotite in the potassic zone suggest a magma degassing process and/or a change in the fluid composition with magmatic water influx to a hydrothermal system.

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