Zircon U–Pb and molybdenite Re–Os geochronology, with S isotopic composition of sulfides from the Chah-Firouzeh porphyry Cu deposit, Kerman Cenozoic arc, SE Iran

Abstract

The Chah-Firouzeh deposit with about 100 Mt ore reserves @ 0.5% Cu is a porphyry copper deposit located 14 km west of the Meiduk deposit in the northern section of the Kerman Cenozoic Magmatic Assemblage (KCMA), southeastern Iran. The mineralization is associated with a porphyry quartz-monzodiorite to quartz-diorite stock, which intruded into Eocene volcanic rocks consisting of andesite, basalt, and andesitic to dacitic tuff. Hydrothermal alteration types in the area include potassic, phyllic, and propylitic varieties. Silicic alteration locally occurred at the surface, while supergene argillic alteration overprinted the other alterations at shallow levels. Mineralization occurs as quartz-sulfide veinlets and stockworks, as well as disseminations in the porphyry body and volcanic host rocks, in association with potassic and phyllic alteration. Hypogene minerals in the deposit include pyrite, chalcopyrite, magnetite, molybdenite, and bornite. Supergene enrichment is irregularly developed in the Chah-Firouzeh deposit. Zircon U–Pb dating of two representative samples from the Chah-Firouzeh porphyry stock yielded emplacement ages of 16.9 ± 0.4 Ma and 16.5 ± 0.2 Ma, respectively. The Early-Middle Miocene epoch marks the most important period of porphyry Cu mineralization in the KCMA. During this period, many adakitic magmas intruded the Eocene volcano-sedimentary sequences and formed some of the largest porphyry copper deposits in Iran, such as Sarcheshmeh and Meiduk. Molybdenite Re–Os dating on two samples separated from "B and D type" veinlets show that mineralization occurred at 16.60 ± 0.06 Ma and 15.99 ± 0.06 Ma, implying a time span of about 0.6 Ma for mineralization. The δ^(34)S values for molybdenite, chalcopyrite, and pyrite from "A, B, and D type" veinlets vary from −1.4 to +2.5‰ suggesting a magmatic source for sulfur. The calculated temperatures for sulfide pairs are compatible with those obtained from fluid inclusion microthermometry and show isotope equilibrium due to fluid evolution.

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