Formation of carbonate-hosted Zn-Pb deposits in collision belts: An example from the Pirejman Zn-Pb + Ba deposit, SE Türkiye

Abstract

The Pirejman region Zn-Pb-Ba mineralizations are located north of Diyarbakır, south of the Bitlis-Zagros Suture Zone, within Upper Cretaceous and Eocene aged units. These mineralizations can be classified into two main groups based on the lithologies and ages of the rock hosting them. Each group is further subdivided into subgroups based on ore type and mineral paragenesis.

The first group developed within the Middle Jurassic-Lower Cretaceous limestone blocks embedded in the Upper Cretaceous aged Ophiolitic Melange. These mineralizations include the Pirejman Main -Zn-Pb deposit, the Sülfür Ocak deposit, and the Mezarlık Tepe deposits. The Pirejman deposit consists of sulfide and oxide‑carbonate Zn-Pb zones. The sulfide zones contain galena, sphalerite, and pyrite, while oxide‑carbonate zones primarily composed of smithsonite, hemimorphite, sericite, and iron oxides. The oxide‑carbonate ore formed as replacements in the adjacent rock and as karst fillings alongside the sulfide ore zone.

The second group of mineralizations developed within the carbonate rocks of Eocene-Oligocene-aged Midyat Group and is further divided into subgroups as barite and Pb-Zn-bearing barite mineralizations. These mineralizations generally occur in vein structures along N30–50°E and vertical fracture zones. They mainly consist of barite, with occasionally occurrences of galena and sphalerite.

The trace element contents of the mineralizations within the melange and Eocene-aged carbonates exhibit significant similarities. Moreover, the stable sulphur isotope values (δ³⁴SV-CDT) of barite and galena from both groups fall within a narrow range of 18–24 ‰ and resembling the isotopic values of MVT Pb-Zn deposits rather than those of SEDEX deposits in similar geological settings.

Field observations and analytical data suggest that the primary mineralization likely formed in the Middle Jurassic-Early Cretaceous interval within passive margin carbonates, probably as MVT Pb-Zn deposits. Subsequently, with the closure of the Neotethys Ocean, the initial MVT mineralizations were transferred into blocks during the Late Cretaceous. As the Neotethys Ocean completely closed during the Miocene, the region underwent uplift and deformation during the collision of the Arabian and Anatolian plates, resulting in thrusts and subsequently normal faulting in an extensional tectonic regime. Hydrothermal fluids circulating along these normal faults remobilized Pb, Zn, and Ba elements from the initial MVT ore bodies within the melange and formed vein-type Ba-Pb-Zn mineralizations along the normal faults. During this process, Pb-Zn mineralizations within the melange oxidized and transformed into supergene oxide‑carbonate Zn-Pb deposits.