SULFUR ISOTOPE STUDY OF SOURCE AND DEPOSITS OF STIBNITE IN THE TURHAL AREA, TURKEY
The Turhal antimony sulfide ore deposits are hosted by a Permain-Jurassic sequence which consists of black phyllites at the base followed by interbedded phyllites and calcareous quartzites with metabasite interlayers and then by brown-gray phyllites with marble blocks. Four different styles and three distinct episodes of mineralization were distinguished according to deposition features of the ores and kinkbands in the stibnite crystals. Stibnite from stratiform, disseminated and vein occurrences as well as pyrite from black phyllites showed the following sulfur isotope composition (delta-S-34): + 2.8 and + 3.0 parts-per-thousand for stratiform stibnite (n = 2), + 3.6 and + 5.5 parts-per-thousand for disseminated stibnite (n = 2), + 2.5 to + 7.8 parts-per-thousand for vein stibnite (n = 11) and -6.1 to + 0.1 parts-per-thousand for pyrite (n = 3). The delta-S-34 compositions of stibnite are interpreted as suggesting an ultimately single source for sulfur in the various styles of mineralization, i.e. synsedimentary volcanic exhalations for the stratiform and disseminated together with ores and hydrothermal mobilisation of these as well as leaching of volcanic rocks to form the vein ores. Deep basinal fluids probably under normal geothermal gradient conditions caused the leaching of the primary sulfides as suggested by the oxygen isotope composition of vein quartz associated with the ores. By contrast sulfur in pyrite is essentially a derivation of seawater sulfate through bacterial and/or chemical reduction.