The Bahariyeh iron oxide copper–gold deposit, Khaf-Khashmar-Bardaskan magmatic belt, NE Iran: Constraints from geochemical, fluid inclusions, and O-S isotope studies

Abstract

The Bahariyeh deposit is located in the central segment of the Khaf-Kashmar-Bardaskan magmatic belt (KKBMB), northeast Iran. Previous U-Pb data on zircon revealed an age of 38–41 Ma for the felsic-intermediate intrusions. The stockwork like vein orebodies are hosted in Eocene monzodiorite porphyry rocks which have strong structural controls imposed by the Great Dorouneh Fault System. Hydrothermal alteration is dominated by silicification, propylitic (chloritization), argillic, and sericitic zones. The mineralized veins in the Bahariyeh deposit can be divided into seven types: 1) quartz ± pyrite; 2) quartz + specular hematite + pyrite ± gold; 3) quartz + chalcopyrite + pyrite; 4) quartz + specular hematite + chalcopyrite + pyrite ± sphalerite ± galena ± gold; 5) chalcopyrite + specular hematite + pyrite ± gold; 6) specular hematite ± pyrite; and 7) chalcopyrite + pyrite. The various vein-style orebodies contain high concentrations of Cu, Au, Pb, Zn, and Ag. Microthermometric measurements of fluid inclusions in mineralized veins demonstrate homogenization temperatures in the range of 271–500 °C (mode of 300 °C), and corresponding salinities in the range of 7.9–26.3 wt% NaCl equivalent. The δ18OWater values calculated from δ18O of quartz, and the δ34S values of chalcopyrite reveal a dominantly magmatic origin for the ore-forming fluids. The fluid inclusions indicate that mixing between magmatic fluids and meteoric water, together with cooling, are the dominant mechanisms for metal deposition in the Bahariyeh district. The combination of ore deposit geology, alteration type, fluid evolution processes, and O–S isotope data suggest that the Bahariyeh deposit be classified as a Cu ± Au-rich iron oxide-copper–gold (IOCG) system.