Abstract

Ali Abad intrusive body is located in Alborz belt, 35 km east of Zanjan. This intrusion with Oligocene age was intruded into the Eocene volcanic and volcano-sedimentary rocks. Based on microscopic studies, this body is quartz-monzogabro to quartz-monzodiorite in composition that represents porphyry to porphyroeid textures. Plagioclase, pyroxene and amphibole are the major minerals of this intrusion which are accompanied with minor biotite, apatite, zircon and opaque minerals. Secondary minerals include sericite, chlorite and calcite that are alteration products. Potassic and silicified alterations as well as Cu mineralization indicate that Ali Abad intrusive body and volcanic host rocks are affected by hydrothermal fluids.