Ali Akbar Hassan-Nezhad

The Qaleh-Zari copper deposit, located in South Khorasan in the Central Lut region of Iran, is a polymetallic vein deposit with major amounts of Cu, Au, Ag and minor amounts of Pb, Zn and Bi. Mineralization occurs in a series of NW-SE trending fault planes and breccia zones in Paleogene andesitic to basaltic volcanic rocks. Argillization, sericitization and propylitization characterize alteration halos bordering mineral veins. The main ore minerals are chalcopyrite, pyrite, galena and sphalerite, with quartz, calcite and minor chlorite as the main gangue phases. Microthermometric measurements of fluid inclusions in cogenetic quartz indicate homogenization temperatures between 160 and 300 °C and salinities from 1 to 4 wt% NaCl equiv. Boiling occurred in the mineralising fluids at 160-1000 m below the paleo-water table at pressures of approximately 15-80 bar at various stages in the formation of the ore body. The wide range of pressures and temperatures reflects the multi-stage nature of the mineralization at Qaleh-Zari. The δ18O values in quartz (relative to SMOW) and δ34S values in chalcopyrite and galena (relative to CDT) range from 6.5 to 7.5‰ and 0.0-1.5‰ (mean: 7.0‰), respectively. At 300 °C, calculated fluid δ18O values are close to 0‰. These data suggest a magmatic origin for sulfur and a surficial origin for the mineralizing fluid. Mineralization at Qaleh-Zari is interpreted as epithermal and low-sulfidation in style and was probably related to a deep-seated magmatic system. Ore deposition was the result of boiling, cooling and pressure reduction. © 2005.