Geology, mineralogy and fluid inclusion studies of the Yamaghan Manto-type Cu (Ag) deposit, southeast Zanjan, NW Iran

The Yamaghan deposit is located in the southeast of Zanjan, within the Tarom subzone of Alborz magmatic belt in NW Iran. The rocks of the area are a collection of Eocene volcano-sedimentary units. Cu (Ag) mineralization in the deposit has occurred as stratabound in the mega porphyritic andesite unit. The main sulfide ores of chalcocite, bornite, chalcopyrite together with pyrite are seen as dissemination, open-space filling, vein-veinlet and replacement textures. Silver sulfide (acanthite) has also been identified based on microprobe studies. Propylitic and mineralization-related alteration types are observed in the deposit. The homogenization temperature of mineralizing fluids was measured in the range 230-390°C, average salinity being 15% NaCl equiv. The Yamaghan deposit formed in three main stages, the first stage occurred at temperatures lower than 100°C during diagenesis, forming framboidal pyrites in the host rock of mega porphyritic andesite. The second stage occurred at temperatures more than 300°C and caused the formation of copper sulfide minerals due to the replacement of pyrite in the first stage. During this replacement, excess iron in pyrite formed as hematite in the place of ores. In the third (or supergene) stage, secondary minerals such as secondary chalcocite, covellite, digenite and copper carbonate minerals such as malachite and azurite formed due to the influence of meteoric water. Based on the geology, host rock, mineralogy, structure and texture, and fluid inclusion data, the Yamaghan copper deposit is similar to Manto-type copper deposits around the world forming through hydrothermal processes.