The Haftcheshmeh porphyry Cu-Mo-Au deposit in the Arasbaran metallogenic belt(AMB) of NW Iran contains more than 185 Mt of ore, with a grade ranging from 0.3% to 0.4%. It is hosted within a porphyritic diorite to granodiorite intruded into an older gabbro-diorite intrusion. 40 Ar/39 Ar analyses of primary magmatic hornblende from the granodiorite porphyry and gabbro-diorite show plateau ages of 26.41 ± 0.59 Ma, with an inverse isochron age of 25.9 ± 1.0 Ma and a plateau age of 27.47 ± 0.17 Ma, with an inverse isochron age of 27.48 ± 0.35 Ma for these two rock types, respectively. Comparing these new age data with those from the nearby Sungun(20.69 ± 0.35 Ma) and Kighal porphyry deposits defines a northwest-southeast Cu-Mo-Au mineralization zone extending for 20 km over the time span of ~27 to 20 Ma. Geochemically, Haftcheshmeh rocks are calc-alkaline with high potassium affinities with tectonic setting in relation to volcanic arc setting. Large ion lithophile elements(LILE) such as Th, U and K show enrichment on a primitive mantle normalized diagram(specially Pb), and are depleted in high field strength elements(HFSE) such as Ti and Nb, pointing to a mantle magma source contamination with crustal materials by subducted oceanic crust.
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