Fluid-Inclusion and Stable-Isotope Characteristics of the Inler Yaylasi Lead-Zinc Deposits, Northern Turkey

Abstract

The Eastern Black Sea Region of Turkey contains over 400 massive (Kuroko-type) and vein-type Cu-Pb-Zn deposits. The Inler Yaylasi lead-zinc deposits are typical examples of the vein type and have been economically mined for 15 years. Three ore veins were identified along E-W-trending fault zones, hosted by extensively altered, Upper Cretaceous volcano-sedimentary rocks. A Tertiary granitoid intrusion occurs near the area of mineralization. The ore veins contain sphalerite, galena, and minor amounts of pyrite, chalcopyrite, fahlore, chalcocite, and covellite as ore minerals, with quartz and calcite as gangue minerals. Fluid-inclusion studies show that the salt composition, salinity, and temperature of the hydrothermal fluids changed during various mineralization episodes. The temperature and salinity of the fluid were high (average temperature of 312.9°C and average salinity of 7.0% NaCl equiv.), and the fluid contained CaCl2, MgCl2, and NaCl during an early episode of mineralization characterized by quartz crystallization. During the sulfide crystallization, temperature and salinity were lower (average temperature of 272.0°C and average salinity of 4.0% NaCl equiv.), and the salts were mainly MgCl2, NaCl, and FeCl2. During subsequent mineralization episodes, temperature and salinity were still lower (average temperature 138.5 °C and average salinity 2.6% NaCl equiv.), and the salt content was dominated by NaCl, Na2CO3, NaHCO3, Na2SO4, and KCl. Oxygen- and hydrogen-isotope results (δ18O; +4.2 to +6.7 ‰ VSMOW and δ D; -83.0 to -59.0 ‰ VSMOW) suggest that magmatic water dominated the ore fluid. It is possible, however, that small amounts of meteoric water and/or formation water of meteoric origin were also involved. This isotopic composition may also be the result of interaction of meteoric water with magmatic rocks, as has been suggested for other deposits in the eastern Black Sea region. The decrease in temperature and salinity of the fluid and the increase in σ18O values of the water from 1725 to 1803 m levels also supports the hypothesis that these deposits formed where upwelling hot fluids met cold surfical fluids.