Author: Necati KARAKAYA, Muazzez Çelik KARAKAYA ve Kevin FAURE
Publishing Date: 2007
Volume: 22 Issue: 1-2
Widespread and intensive hydrothermal alteration is associated with volcanogenic massive sulfide and vein type sulfide deposits are generally observed thought the Eastern Black Sea province. Samples were collected from many localities in the province for bulk-rock and clay fraction Xray diffraction (XRD), scanning electron microscopy and energy dispersive X-ray (SEM-EDX), dry chemical analyses were made.
Clay mineral assemblages are observed in and around of Late Cretaceous volcanic rocks composed of basaltic, andesitic, dacitic, rhyodacitic and rhyolitic lavas and pyroclastics are often spatially associated with Late Cretaceous-Paleocene granitoid intrusion. Hydrothermal alteration of the volcanic rocks resulted in the formation of propylitic, phyllitic (seritic) and, argillic alteration along with hematite, silica polymorphs and, alunite mineralization. Alunite, kaolinite, gypsum, pyrite and native sulfur are abundant in high sulfidation zones, kaolinite and silica are abundant in the argillic alteration and sericite (illite) dominates in the phyllic alteration. Some of kaolinite occurrences are composed of kaolinite, silica polymorpps and partly illite. Other kaolinites were seen as veins and their thickness are between 5 to 30 cm and white to light green in color.
Illite minerals are generally 2M polytype and their crystalinity are good. Oxygen isotope values of illite minerals range between 6 and 8 ‰ (V-SMOW) and suggest deposition from seawater at elevated temperatures (200-300 °C). Oxygen isotope values of the kaolinite veins range between 16 and 17 ‰. The veins were most likely formed at temperatures of 75 to 100 °C in equilibrium with water that has values similar to those of seawater (0 ‰). Two type of bentonite occurrences in the alteration were defined zones and generally contain Ca-montmorillonite. First type of the bentonite deposits which are greenish yellow colored consists of nearly pure montmorillonite whereas second type which is white to purple ones contain minor amounts of silica polymorphs (% 5-10) besides to Ca-montmorillonite. Oxygen isotope values of montmorillonite from the bentonite deposits range between 23 and 29 ‰ clear evidence of formation by halmyrolysis. Na and K are found in Ca-montmorillonites in generally all of bentonite occurrences.
Key Words: Black Sea; clay minerals; hydrothermal alteration; illite; kaolinite; montmorillonite