Study of ore mineralization of polymetallic veins of the Qarah Changal area, northwest of Qazvin

The vein-type mineralization of the base (Zn, Pb, and Cu) and precious metals (Au) in the Qarah Changel area (northwest of Qazvin) is located in the southern part of the Tarom-Hashtjin metallogenic belt. Volcanic (trachy-andesite, rhyolite and dacite) and pyroclastic (tuff, tuffite and tuffaceous shale) (Eocene) rocks are the hosts of this mineralization. Distinctive alterations around mineralized veins include argillic, sericitic, propylitic and silicic. Ore mineralization has occurred in two forms, hypogene and supergene. Hypogene ore minerals include sphalerite, galena, chalcopyrite, pyrite, magnetite, gold, digenite, and bornite, which are associated with supergene mineralogical assemblages such as calcocite, covellite, cerussite, malachite, azurite, hematite, and goethite. Calcite and quartz are the associated gaugues of this mineralization. The texture of the ore consists of vein-veinlet, replacement, breccia, disseminated, bladed and open space filling. According to geochemical studies, volcanic host rocks are peralumine and have the nature of high- potassium clac-alkaline to shoshonitic. The enrichment of K, Ba and Cs in comparision to Ti, Nb and Zr, the LREEs enrichment relative to HREEs, and the occurrence of negative Nb anomaly indicate the formation of a magma generating volcanic rocks in the subduction zone. Studies of fluid inclusions in quartz mineral co-genetic with sulfide ore minerals showed that they are chiefly of L+V and having homogenization temperature in the range of 202 to 247 C°. The salinity of fluid iinclusions also ranges from 10 to 22 wt% NaCl eq. According to microthermometric data, boiling and cooling are the most important mechanisms in the development of mineralized veins. Evidence such as the coexistence of liquid and vapor-rich fluid inclusions, hydrothermal breccias, microcrystalline quartz and bladed calcite confirm the occurrence of the boiling phenomenon during the formation of mineralized veins. Combining the results of mineralogical studies, texture and associated alterations, geochemistry and tectonic setting of volcanic rocks, and   microthermometry of fluid inclusions indicate that  mineralization in the Qarah Changel area is most similar to low sulfidation-type epitermal ore deposits.