Metallogeny of Manto-type stratabound Cu-(Ag) mineralization in Iran: Relationship with NeoTethyan evolution and implications for future exploration

Abstract

Stratabound or “Manto-type/volcanic red-bed” Cu-(Ag) deposits occur along the Urumieh-Dokhtar magmatic arc (UDMA), Sanandaj-Sirjan Zone (SSZ), Alborz Magmatic Assemblage (AMA), Sabzevar Zone, and Lut Block structural zones of Iran, and are hosted by Cretaceous and Eocene volcanic and volcano-sedimentary rocks. The most important deposits of this type are East Narbaghi, Khankishi, Kahak, Veshnaveh, and Koshkouieh in the UDMA; Keshtmahaki in the SSZ; Mari, Qeblebolagh, and Yamaghan in the AMA; Abbasabad, Dochileh, Gol-Cheshmeh, Zangaloo, Abri, Rahbari, and Cheshmeh-Marzieh in the Sabzevar Zone; and Vorezg in the Lut Block. Back-arc extensional basins are the principal tectonic setting for the Manto-type deposits of Iran, that developed during the subduction of the NeoTethyan crust beneath the Iranian micro-continental plates. The stratigraphic sequences of these deposits are commonly formed from volcanics, volcaniclastics, and sedimentary rocks, which are similar to other volcanic-hosted stratabound copper districts around the world. Iranian Manto-type deposits are stratigraphically controlled in which Cu-(Ag) mineralization occurs as vein-veinlets, disseminated grains, and filling vesicles. Copper mineralization is commonly closely related to framboidal pyrite and pyrobitumen. The mineralogy of the Cu-(Ag) mineralization in all Manto-type deposits of Iran is simple and consists of chalcocite, bornite, native copper, chalcopyrite, acanthite, and minor secondary digenite, covellite, cuprite, tenorite, chrysocolla, anilite, malachite, azurite, and Ag-bearing clausthalite as the main economic minerals, accompanied by pyrite, chlorite, calcite, quartz, and zeolite. Copper sulfides occur mainly as a replacement of diagenetic pyrite, which in turn, replaced pyrobitumen. Iranian Manto-type deposits are interpreted to be the result of mineralizing hydrothermal fluids derived from footwall volcanic rocks that migrated upwards, driven by the late diagenetic processes. The UDMA and Sabzevar Zone are the most favorable metallogenic provinces in Iran for Manto-type Cu-(Ag) exploration since these two zones host the largest copper deposits of this type, including Abbasabad, Koshkouieh, East Narbaghi, and Abri deposits. Consequently, reconstruction of orebearing basins, such as presented, is not only critical to understanding the genesis of ancient deposits and their tectonic setting, but also for guiding exploration in deposit-proximal areas.