Hydrothermal evolution of Darrehzar porphyry copper deposit, Iran: evidence from fluid inclusions

The Darrehzar porphyry Cu-Mo deposit is located in Southwestern Iran (∼70 km southwest of Kerman City). The porphyries occur as Tertiary quartz-monzonite stocks and dikes, ranging in composition from microdiorite to diorite and granodiorite. The Darrehzar stock is highly altered, and even in the outermost part of the intrusion, it is not possible to find completely fresh rock. Surface weathering was developing ferrous Fe-rich lithologic units in leached zone and concentrated copper minerals in supergene zone. Unlike eastern areas which do not account for deep faults, the supergene zone is well developed in western areas with maximum of 118 m thickness. Hydrothermal alteration and mineralization at Darrehzar are centered on the stock and were broadly synchronous with its emplacement. Early hydrothermal alteration was dominantly potassic and propylitic, and was followed by later phyllic and argillic alteration. The hydrothermal system involved both magmatic and meteoric water and boiled extensively. Copper mineralization was accompanied by both potassic and phyllic alteration. Four main vein groups have been identified: (I) quartz + pyrite ± molybdenite ± anhydrite ± K-feldspar ± chalcopyrite ± bornite ± Cu and Fe oxidic minerals (peripheral); (II) quartz + chalcopyrite + pyrite + molybdenite; (III) quartz + pyrite ± calcite ± chalcopyrite ± anhydrite (gypsum); and (IV) quartz or calcite, gypsum or ± pyrite. Based on abundance, nature, and phases number observed at room temperature, three types of fluid inclusions are typically observed in these veins: (1) vapor-rich, (2) liquid-rich, and (3) multi-phase. Early hydrothermal alteration was caused by high temperature, high salinity orthomagmatic fluid and produced a potassic assemblage. Phyllitic alteration was caused by high salinity and lower temperature orthomagmatic fluid. Magmatic and meteoric water mixture was developed in the peripheral part of the stock and caused propylitic alteration which is attributed to a liquid-rich, lower temperature.