Lead and sulfur isotope evidence for the origin of the Inler Yaylası lead–zinc deposits, Northern Turkey

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. The measured δ34S values of galena (−3.9 to −1.9 ‰V-CDT) and sphalerite (−2.0 to +0.4 ‰V-CDT) and calculated δ34S values of H2S in equilibrium with these mineral (−2.14 to −0.73 ‰V-CDT) are slightly lower than the magmatic sulfur values and suggest an indirect magmatic source, that would involve the leaching of isotopically lighter sulfur from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit. Lead isotope ratios, for galena samples are dispersed in a narrow range from 18.639 to 18.676 (206Pb/204Pb), 15.671–15.698 (207Pb/204Pb) and 38.761–38.870 (208Pb/204Pb). These lead isotope data are close to those of an orogene reservoir and are very different from those of a mantle-related reservoir. In the light of these observations it may be assumed that the sulfur and lead concentrated in the studied deposits was leached by deep circulated meteoric water from either the Upper Cretaceous volcano-sedimentary rocks or a deep seated, older sulfide ore deposit which contained light magmatic sulfur and orogenic lead.