Generation of the Zarshuran Gold Deposit in Northwest Iran Triggered by Exhumation of the Iman Khan Metamorphic Core Complex

Abstract Zarshuran is the largest gold deposit in the Middle East. However, the structural controls and ore-forming processes at Zarshuran remain poorly understood. This study presents new geologic mapping results, detailed descriptions of ore textures, and calcite in situ U-Pb dating and thermochronological data to propose a new genetic model addressing the knowledge gap. New field mapping results demonstrate that the Zarshuran deposit is hosted in the Iman Khan Complex, which exhibits abundant ductile fabrics, and gold mineralization is spatially associated with the Zarshuran fault separating the Neoproterozoic Iman Khan and Cambrian Chaldagh units in its footwall from the Cambrian Zarshuran unit and Oligocene-Miocene Qom Formation in its hanging wall. Ore textures include syntectonic gold-bearing pyrite veins around felsic porphyroclasts, syntectonic cata-clastic flow around lenses, syntaxial euhedral calcite, and pyrite veins filled in brittle fracture and stratabound within the Qom Formation. Muscovite-quartz schist of the Iman Khan Complex underwent peak metamorphism of greenschist facies at pressure-temperature (P-T) conditions of 0.20 to 0.44 GPa and 372° to 446°C as constrained by chemical compositions of muscovite. The 40Ar/39Ar dating of syntectonic muscovite yielded a plateau age of 20.59 ± 0.32 Ma. In situ U-Pb dating of calcite associated with gold-bearing pyrite yields 14.5 ± 2.0 Ma. Apatite (U-Th)/He ages range from 12.73 ± 0.77 to 5.55 ± 0.46 Ma. These ages, combined with HeFTy thermal modeling, suggest that the Zarshuran deposit underwent a slow cooling stage from 20.6 to 14.5 Ma, a rapid cooling stage from 14.5 to 9 Ma, and an extremely slow cooling stage at <9 Ma. We propose that the Iman Khan Complex is an incipient metamorphic core complex (MCC), and gold mineralization occurred in the ductile and brittle deformation stages (20.6–14.5 Ma) associated with exhumation of the Iman Khan MCC. Other MCCs in the Tethyan metallogenic belt may be potential gold exploration targets.