Sulfur isotope geochemistry of the Chodarchay Cu-Au deposit, Tarom, NW Iran

Abstract

The Chodarchay porphyry–high-sulfidation epithermal Cu-Au deposit in the Tarom subzone of the western Alborz structural zone of NW Iran is related to quartz-monzonite and alkali-granite intrusions that were emplaced within the volcanic-volcaniclastic rocks of Karaj Formation during Tertiary. The Chodarchay deposit formed as a high-sulfidation epithermal overprint on porphyry type mineralization. The mineralization occurred as stockwork, dissemination, veinlet, open space filling and breccias. Chalcopyrite, pyrite, sphalerite, and galena are the main sulfide minerals in the area. The sulfur isotope composition of sulfide minerals from the Chodarchay deposit is positive, ranging from 0.2 to 6.8 ‰. The sphalerite-galena isotope geothermometer shows 360 °C for the crystallization temperature. Sulfur was sourced from a homogeneous magma, and its isotopic composition decreases with depth and temperature decreasing due to fluid oxidation changes. Therefore, sulfur isotope assemblages show a systematic spatial distribution within the Chodarchay system.