Fluid inclusion and stable isotope study of the Khalyfehlou copper deposit, Southeast Zanjan, Iran

Abstract

The Khalyfehlou deposit is one of volcanic-hosted vein-type Cu deposits located in the Tarom metallogenic zone, NW Iran. The host rocks are part of an Eocene volcano-sedimentary sequence formed into a NE–SW trending anticline with the Khalyfehlou deposit in its axis. The main ore minerals are chalcopyrite, bornite, chalcocite, and covellite and the gangue minerals are quartz, sericite, and calcite. This paper attempts to identify the source of the mineralizing fluids by using sulfur and oxygen isotope data and fluid inclusion studies. Two-phase liquid-rich fluid inclusions in the quartz gangue associated with the sulfide veins were studied and interpreted. Homogenization temperatures for these inclusions range from 159 to 293 °C and salinities are between 14 and 19.3 wt% NaCl equivalent. The sulfur isotope values for the chalcopyrite range from −2.0 to −5.3 ‰. Negative sulfur isotopes values and the occurrence of framboidal pyrite in the tuffaceous sandstone host rocks suggest a sedimentary origin for the sulfur. The oxygen isotope composition of quartz from the veins ranges from 12.3 to 14.3 ‰. The δ18Ofluid values calculated from the oxygen isotope data and the mean value of the homogenization temperatures range from 0.6 to 3.6 ‰. The constant fluid salinities at the whole range of temperature values and the H–O isotopic characteristics indicate that the ore-forming fluid for the Khalyfehlou deposit was relatively high salinity recirculating Ca–Na-rich meteoric-formational water. This study suggests that mineralization at the Khalyfehlou deposit is similar to cordilleran vein-type deposits. As such and based on the fluid inclusion data and other geological data, the cordilleran-type Khalyfehlou deposit would have been emplaced by a mesothermal system.