Tashvir ore occurrence, NE Zanjan: Intermeiate-sulfidation style of epithermal base metal (Ag) mineralization in the Tarom-Hashtjin zone

Tashvir ore occurrence, 75 km northeast of Zanjan, is located in the Tarom-Hashtjin subzone. Mineralization occurs as ore-bearing quartz vein-veinlets within the Eocene tuffs and andesitic lavas (equal to Karaj Formation). Ore minerals include chalcocite, chalcopyrite and galena, and quartz, calcite and chlorite are present as gangue minerals at Tashvir. The ore show vein-veinlets, breccia, disseminated, replacement, relict, colloform, crustiform, dog tooth and plumose textures. Four stages of mineralization can be distinguished at Tashvir. These stages are progressed from quartz- chalcocite- chalcopyrite- galena‒cemented veins and breccias (stage-1), individual or sets of quartz veinlets (stage-2), and vug infill calcite (stage-3) and chlorite (stage-4) vein-veinlets. Hydrothermal alteration consist of silicified, argillic, carbonatic and chloritic. In the outer parts of the mineralization zones, alteration is propylitic. Similar REE patterns of the mineralized veins and the host rocks indicate they are genetically related. Enrichment of ore-forming elements (Ag, Cu, Pb, Zn) in ore zones is specifies leaching of elements from altered host rocks to ore zones. Characteristics of Tashvir ore occurrence are comparable with intermediate-sulfidation style of epithermal base metal (Ag) deposits. Mineralization at Tashvir and other epithermal deposits of the Tarom-Hashtjin subzone took place as a result of hydrothermal activity related to the late Eocene magmatism, and is controlled by fault systems. Therefore, investigation of the altered Eocene volcanic and volcano-sedimentary rocks, especially at the composite place of granitoid intrusions and along the fault structures, became the most favorable locus for epithermal ore bodies at Tarom-Hashtjin subzone.