Geology, mineralogy, and fluids inclusion studies in Shadan coppergold deposit, Southern Khorasan

Shadan copper-gold deposit is located in nearly 65km Southwest of Birjand. The area is a part of eastern margin tertiary volcanoplutonic belt in Lut Block. The oldest units in this area are tertiary andesite, tuff, rhyolite, and rhyolitic tuff. The units are intruded by late Eocene–Oligocene quartz monzonite-granodieritic (Shadan porphyry), granite, and granodiorite intrusion rocks. The rocks are again overlined by Quaternary deposits. Shadan deposit is considered as Cu-Au porphyry in which mineralization was controlled by tectonic structures. The deposit is hosted by dacite, rhyodacite and quartz monzonite and granodiorite rocks which are mainly associated with potassic, sericitic, argillic and propylitic alterations. Mineralization mostly occurs as disseminated, stockwork, veins and veinlets in the host rocks. The paragenesis in veins and veinlets includes quartz, pyrite, chalcopyrite, bornite, chalcocite, pyrrhotite, magnetite, hematite and covellite, gold, malachite and iron-hydroxides. Gold grains are between 1 to150μm in diameter commonly occurring within the quartz and in some places occur in 10μm diameter within oxidized pyrites. Fluid inclusion studies on 5 types of fluids reveal that homogenization temperatures range between 150 and 500°C (Average 350°C) with salinity from 10 to 60wt.% NaCl equivalent. Field observation and laboratory studies suggested that the mineralization likely belongs to porphyry magmatic-hydrothermal systems.