Structural analysis of the Takiyeh Zn-Pb mine in the Malayer-Esfahan metallogenic belt, west Iran

The Malayer-Esfahan metallogenic belt is one of the main Zn-Pb mineral regions of Iran which is in the central part of the Sanandaj-Sirjan zone (Rajabi et al., 2012). The Sanandaj-Sirjan zone has long-lived magmatism and deformation related to the Mesozoic subduction and the middle Miocene collision. The rocks in this zone are the most highly deformed ones in the Zagros orogen (Mohajjel and Fergusson, 2014). Most of the sediment-hosted Zn-Pb deposits of the Malayer-Esfahan metallogenic belt are hosted within extensive Early Cretaceous platform carbonates deposited during an extensional back-arc basin (Rajabi et al., 2012). As the Zn-Pb deposits were initially formed in an extensional setting, subsequent compressional phases of the Eurasian and Arabian continental collision have deformed these deposits. It is the inversion tectonic phase that has played an important role in the evolution of the orogenic belts (Zanchi et al., 2006). In this study, the role of fault systems especially the inverted faults in the Takiyeh Mine has been studied. This mine is located in the NW part of the Malayer-Esfahan metallogenic belt, close to the Takiyeh village.

In this study, faults of the area were distinguished using orthotropic images to investigate the relationship between tectonic structures and mineralization in the Takiyeh Zn-Pb mine. Geometry and kinematics of these faults have been studied during several field observations. Then, the study of polished sections, Zn-Pb analysis from all sections of the mine and XRF and XRD methods have been done for ore mineralization.

The Zn-Pb mineralization in the Takiyeh mine occurs in the Ksl ore-bearing unit of the Lower Cretaceous. The Kl unit is thrusted over the Ksl unit during the compressional phases of the continental collision between the Arabian-Eurasian plates. Mineralization is composed of mineral veins of several centimeters to several meters along the main faults of the study area. Generally speaking, two systems of faults with NE-SW and NW-SE trends have caused deformation and controlled mineralization in the Takiyeh mine. The faults with NE-SW trend cut the NW-SE trend faults, indicating activation of the NE-SW faults in a new stress field. The main fault trends of the study area are most frequent in the N60W and N30E to N50E trends. The dip angle of the NW-SE trend faults generally change between 60 to 70 degrees toward the northeast. These faults are generally steep reverse faults due to the fault plane indicators such as direction of roughness and softness of fault surface. The dip angle of the NW-SE trend faults are generally toward the SW and these fault are exposed as steep fault zones. The SC fabric in these faults indicates reversed and steep movement, causing displacement of the NW-SE mineral veins.Generally, mineralization in the Takiyeh mine has been formed during the Lower Cretaceous extensional phases. So, this region had experienced the extensional regime and normal faults have controlled the upward migration of the hydrothermal fluids and mineralization. Mineralization in the study area is hosted by the Lower Cretaceous unit (Ksl). It is noteworthy that the formation of Zn-Pb mineralization in an extensional setting and subsequent compressional orogeny phases, especially the middle and upper Cretaceous orogeny phases, such as the Laramide orogeny phase, has affected the area under compressional settings. Thus, the inversion tectonic in the study area inverted the low-angle normal faults to steep reverse faults. Generally, inversion tectonic is a common process in regions of continental collisional involving the reactivation of major extensional normal faults as reverse faults. Inversion of a normal fault causes deformation transfer to the fault footwall via shortcut thrusts. The outcrop of some shortcut thrusts in the western part of the Takiyeh mine are evidences of inversion tectonic in the study area. These shortcut faults with NW-SE trend and dip angle toward NE have caused deformation of the Cretaceous calcareous units. In fact, these reverse shortcut faults have been normal faults that formed initially under the Cretaceous extensional regimes and then they became inverted under later compressional phases. The inversion tectonics in the study area, in addition to the formation of shortcut thrusts, has deformed the Ksl unit and steep reverse fault and folding has been formed by progressive deformation. The folded structures in the study area in ductile shaly units have been formed as small Z-shaped folds between fault shear zones. Although these folded structures have been formed between parallel fault zones, several minor faults older than these folds are exposed in some parts of the study area due to the activity of these faults. These older faults have been previously formed between the Ksl unit and were folds during the progressive stages of the inversion tectonic.