Sulfur isotope geochemistry and mineralogy of Balcilar vein type barite-sulphide mineralization, Biga peninsula, NW Turkey

The Balcilar (Canakkale) barite-galena mineralization is a typical example of the vein type barite-lead-zinc deposits in the Biga Peninsula. The lithologic units in the study area are Akcaalan andesite, Eocene, Adadagi pyroclastics, Oligocene, Dededag dacite, Miocene, Karaomerler basalt, Plio-Quaternary and alluvium Quaternary. Barite-galena veins occurred along the faults developed within the andesites. Barite, quartz and galena are main minerals and are accompanied by minor amounts of sphalerite, pyrite, chalcopyrite, covellite and marcasite. The earliest barite (barite I) occurs as coarse-grained subhedral-euhedral crystals and the later (barite II) as small tabular crystals in between the earlier coarse crystals. Quartz occurs as fine-grained crystals with the later small barite crystals. Galena, sphalerite, chalcopyrite, pyrite, marcasite and covellite occur open spaces within the earlier barite (barite I) crystals. Sulfur isotopes indicate that in galena the reduced sulfur from bacterially or inorganically reduced sulphate, or from an isotopically light reduced S-source. The δ34SH2S values calculated from the barite-H2S and galena-H2S fractionation factors, in the same samples, indicate a temperature of between 200 and 300 °C. Relatively lower δ34S values of barites than dissolved sulphate in modern oceans or Eocene sea waters have been evaluated as the ore forming hydrothermal fluids were derived from interacting throughout the magmatic host-rocks.