Sulfur-isotope characteristics of the volcanogenic Cu-Zn-Pb deposits of the Eastern Pontide Region, Northeastern Turkey
In the Eastern Pontide Region of northeastern Turkey, volcanogenic Cu-Zn-Pb deposits of the Kuroko type are widespread within the dacitic series of the Liassic-Eocene volcano-sedimentary succession. Sulfide mineralization within the studied deposits shows four different depositional styles: disseminated ore; polymetallic stockwork ores; polymetallic massive ores; and disseminated pyrite in the hanging-wall tuff units. Only the stockwork and massive ores are economically important, and usually one or the other dominates in each ore body. The delta(34)S of sulfide minerals belonging to the various styles of mineralization are in the range fi om -2.6 to +5.2 parts per thousand (VCDT): pyrite has the highest values and the galena lowest values in agreement with the usual isotopic-fractionation trends. Massive ores have heavier sulfur-isotope composition among the mineralization styles and the heaviest values are recorded in barite- and gypsum-rich deposits. The close similarity of the delta(34)S among the various mineralization episodes in some deposits indicates a single sulfur source having a stable and homogenous composition. The delta(34)S of sulfates fall into three groups: barites and primary gypsum (15.4 to 20.4 parts per thousand). close to coeval seawater sulfate: one value: of barite (25.4 parts per thousand) heavier than coeval sea water; and values of secondary gypsum (2.2 to 8.0 parts per thousand) either very light compared to coeval seawater sulfate, or within the range recorded from sulfide minerals. The delta(34)S values of pyrite disseminated in the brecciated dacite tuff units are very close to zero and similar to the ones reported for magmatic rocks, suggesting a magmatic source for the sulfur of the earliest sulfide mineralization episode. These delta(34)S data are not sufficient to calculate the fraction of the reduced sulfur derived from seawater sulfate, as the associated fractionation factor cannot be constrained.