Microthermometric and O‐ and H‐isotope characteristics of the mineralizing fluid in the Akgüney copper–lead–zinc deposit, NE Turkey

Abstract

The Akgüney copper–lead–zinc deposit (Ordu Province) is actively mined in the eastern Black Sea Region of Turkey. This deposit consists of ore‐bearing veins emplaced along fault zones and hosted by slightly altered Upper Cretaceous andesites. Seven ore veins, D‐1 to D‐7, have been identified. These veins strike N 70–80°W with a dip of 50–60°NE, except for D7 which strikes E–W with a dip of 25°S. The ore‐bearing quartz vein outcrops are slightly limonitized and hematitized. Two different ore associations are distinguished within the D‐1 and D‐2 veins. The first contains only pyrite, whereas the second consists of coarse‐grained sulphides such as chalcopyrite, galena, sphalerite, tetrahedrite, and secondary limonite veinlets in addition to pyrite. Quartz and calcite are the gangue minerals. The mineral paragenesis has been identified as: pyrite→galena→chalcopyrite (I)→sphalerite→chalcopyrite (II)→(tetrahedrite ?)→quartz→calcite. Fluid inclusion data indicate that the ore‐forming fluids contained significant concentrations of divalent cations in addition to NaCl. The salinity of the fluids lies in the range 14–24% (ave. = 19.0) NaCl equivalent; liquid homogenization temperatures range from 276 to 349°C (ave. = 307°C) and decrease to 211°C through the later stages of mineralization. Oxygen and hydrogen isotope data are consistent with the mineralizing fluid being of meteoric origin, with modification of the oxygen isotope composition by exchange with the volcanic host rocks. However, low δD values suggest a magmatic water component in some samples. The combination of fluid inclusion and stable isotope data suggest that the Akgüney Cu–Pb–Zn vein‐type deposits were formed by the leaching of metals and sulphur from the surrounding volcano‐sedimentary rocks by deep‐circulating meteoric water.