No abstract

We obtained sulfur isotope analysis results of sulfide samples from hydrothermal vent chimneys of the eastern Pontide volcanogenic massive sulfide (VMS) deposits. The total range of δ 34 S values for vent chimneys in the eastern Pontide VMS deposits is -2.7 to 6.5 per mil. Sulfide δ 34 S values show narrow variation in the Lahanos, Killik, and Kutlular deposits, but wider variation in the Kızılkaya and Çayeli deposits. The δ 34 S values of sulfides in Çayeli chimney samples gave a slightly higher range than the other Pontide chimney samples. In some samples, a rough isotopic zonation pattern was observed throughout chimney zones. Variations in δ 34 S values of sulfides within chimney walls were probably caused by chemical reactions of reprecipitation and replacement between vent fluids and earlier sulfide minerals in the chimney. Ranges of δ 34 S values of sulfide minerals are similar for different deposits within the same region. Variations in the δ 34 S values of the Pontide deposits appear to be geographic rather than stratigraphic. The sulfur isotope values of the deposits have a narrow compositional range, indicative of a fairly specific origin. Although "deep-seated" sulfur may be a potential source in the Pontide district, a significant contribution of seawater sulfate cannot be ruled out. The δ 34 S values of selected samples from Pontide vent chimneys are within the range of sulfur values obtained from Phanerozoic VMS deposits. The range is similar to, but slightly broader than, the range of values reported for modern vent chimneys and ancient vent chimneys from the Yaman-Kasy deposit.

Metalliferous sedimentary rocks, despite being limited in scope, are important stratigraphic horizons within the volcanogenic massive sulfide (VMS) deposits in the Upper Cretaceous volcanic belt of the Eastern Pontides. The metalliferous sedimentary rocks compose a distinctive genetic class. The abundance of such rocks in the Eastern Pontide district provides a basis for study and description that may be more widely applied in other VMS districts. The metalliferous sedimentary rocks generally form layers less than 1.5 m thick above stratiform massive sulfide ores. The metalliferous sediments are largely composed of quartz and hematite. While the Si ± Fe content of sediments directly overlying the stratiform massive sulfide ores is high, an increase in the amount of carbonate is observed in sediments that are not directly overlying the ores. The metalliferous sedimentary rocks were formed by the mixing of mainly chemical components and to a smaller degree detrital components in various proportions due to sedimentation processes occurring on the seafloor. Of the major constituents of the metalliferous sediments, Si, Fe, Cu, Zn, Pb, Sb, and Au generally have a hydrothermal origin, whereas Al, Zr, and Ti are from detrital volcanic and volcaniclastic components. The high levels of U and V indicate a seawater origin, pointing to a submarine environment for the formation of the Eastern Pontide metalliferous sedimentary rocks. The composition of the metalliferous sediments of Eastern Pontide VMS deposits implies that these sediments carry a continental-arc provenance signature. Silica (±iron)-rich rocks in the Eastern Pontides can be used as guide horizons in exploring for volcanogenic massive sulfide deposits in the district since they formed close to the sulfide ores and their areal extents are much greater than those of the sulfide ores. In comparison with their analogues on a global scale, these rocks are broadly comparable to silica-and iron-rich sedimentary rocks in the VMS-bearing districts of the Urals.

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Four porphyry Cu-Mo systems were investigated by Re-Os molybdenite geochronology to constrain their timing with respect to the geodynamic and magmatic evolution of the eastern Pontides, Turkey. Molybdenite from the Ispir-Ulutaş deposit yielded an Re-Os age of 131.0 ± 0.7 Ma, which is consistent with Early Cretaceous U-Pb laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon ages of local calc-alkaline intrusions. It demonstrates that porphyry deposits were already formed during Early Cretaceous subduction of the Neotethys along the eastern Pontides, and that they can be correlated with porphyry Cu events in the adjacent Lesser Caucasus. Molybdenite Re-Os ages of 76.0 ± 0.4 and 75.7 ± 0.4 Ma at the Elbeyli prospect and 77.2 ± 1.0 Ma at the Emeksen prospect overlap with U-Pb LA-ICP-MS zircon ages of shoshonitic to high-K calc-alkaline intrusions in the region, which were emplaced during Late Cretaceous Neotethys subduction. A 50.7 ± 0.3 Ma molybdenite Re-Os age at the Güzelyayla deposit confirms porphyry Cu-Mo emplacement coeval with Eocene postcollisional, calc-alkaline adakitic magmatism of the eastern Pontides. An electron microprobe study of molybdenite samples, supplemented by data obtained during Re-Os dating, shows that the Eocene Güzelyayla deposit and the Late Cretaceous Emeksen prospect have the highest Re enrichment. Postcollisional melting of a thickened mafic lower continental crust and melting of a metasomatized lithospheric mantle with little to no interaction with upper crustal rocks may explain the Re enrichment at Güzelyayla and Emeksen, respectively.