Metallogeny of Cretaceous carbonate-hosted Zn–Pb deposits of Iran: geotectonic setting and data integration for future mineral exploration

More than 285 carbonate-hosted Zn–Pb deposits occur in Iran, including world-class deposits such as Mehdiabad and Irankuh. Cretaceous carbonates are the most common host rock for these deposits, which are largely concentrated in the Malayer-Esfahan metallogenic belt (MEMB) and the Yazd-Anarak metallogenic belt (YAMB) and, to a lesser extent, in the Central Iranian geological and structural gradual zone and in the Central Alborz metallogenic belt. To erect a broad metallogenic framework for Cretaceous-hosted Zn–Pb resources in Iran, we integrated a geographic information system data base, including all reported deposits and occurrences of this affinity. A significant correspondence between the distribution of these deposits and the main suture zones in the Iran plate is clearly indicated. In addition, stratiform laminated sulphides are common features in most of the Early Cretaceous deposits (e.g. Irankuh, Ravanj, and Anjireh-Tiran), indicating a synsedimentary origin of these deposits. Most of the Cretaceous-hosted orebodies cluster around the Nain-Baft and Sabzevar Cretaceous suture zones and are associated with two major tectonic events: (1) extensive Early Cretaceous back-arc basin formation, producing, for instance, the Nain-Baft mineralized basin and (2) compressive Late Cretaceous closure of the back-arc basins, reflecting the Laramide orogenesis, for example, around the Nain-Baft and Sabzevar sutures in the west and north of the Central Iranian Microcontinent. Related to the back-arc basin formation and evolution, stratiform sedimentary exhalative (SEDEX)-like (e.g. Irankuh, Vejin, Robat, Takiyeh, and stratiform Ravanj) and Irish-type (e.g. Mehdiabad) Zn–Pb ± Ba deposits formed, whereas basin closure and plate collision triggered basinal fluid flow from the suture towards both sides of the MEMB and the YAMB, thus causing the formation of Late Cretaceous-hosted Mississippi Valley-type provinces (e.g. Nakhlak, stratabound Ravanj, Khanjar-e-Reshm, Chahriseh, and Lapalang deposits) on both sides of the Nain-Baft suture zone. These two different geotectonic scenarios and their evolution explain the distribution pattern of most of the Zn–Pb deposits hosted by Cretaceous sedimentary rocks in Iran. On the other hand, the formation of these deposits is not related to the collision between the Arabian and Iran plates (including the Sanandaj-Sirjan zone), inasmuch as no spatial relationship exists between this tectonic event and the distribution pattern of the deposits, which occurs far away from the collision front. The occurrence of SEDEX-like deposits in continental back-arc basins of the Iran plate confirms that an extensional setting favourable for regional Zn–Pb metallogenesis prevailed during the Early Cretaceous. In addition, Irish-type Zn–Pb mineralization took place in carbonate platforms developed on the passive margins that surrounded the Nain-Baft back-arc oceanic basin (e.g. Mehdiabad deposit).

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