Sulfur isotope compositions of the polymetallic ores of massive sulfide deposits in the Asian areas of Russia

A large group of the massive sulfide deposits of different ages with variou s reserves of lead and zinc including some unique deposits is situated in t he Asian areas of Russia. These deposits are related to a submarine volcani sm of bimodal or differentiated series. Volcanogenous deposits referred to as a VHMS-type and volcanogenous-sedimentary deposits considered to be a tr ansiting group to the deposits of a SEDEX-type are distinguished among them . Volcanogenous deposits are closely associated with crater and subvolcanic bodies of rhyolite-porphyries and are formed at a replacement of weakly li thificated bentonic sediments or due to the deposition of ores directly fro m the ore-feeding channels on the sea floor. They bear the features of the Kurokotype deposits. Volcanogenous-sedimentary deposits are located in the distal facies of the volcanic sequences and were formed in a hydrothermal-s edimentary way from the near-bottom ore-bearing brines according to the Red Sea model or due to a deposition of the dispersed sulfide particles carrie d out by plumes of hydrothermal systems on the sea floor. Ores of the depos its of the volcanogenous group have a more homogenous sulfur isotope compos ition of sulfides. Average values of delta(34)S range from -2.8 to +8.8 par ts per thousand. Magmatic sulfur directly supplied by a fluid or sulfur of magmatic sulfides are considered to be a principal source for these deposit s. A slight increase in a heavy sulfur isotope composition of early sulfide s and sulfates relative to late minerals is revealed in the long-lived ore- forming systems. This phenomenon is explained by an increase of a contribut ion of sulfur from the marine water sulfates to the ore-forming systems. A correlation of the sulfur isotope composition of barite and the marine wate r sulfates of the same age is established. Volcanogenous-sedimentary large- scale deposits have the heavy sulfur. The delta(34)S values vary within a w ide range from +13 to +21 parts per thousand and display an unimodular dist ribution with the average delta(34)S values of +12.8 to +13.6 parts per tho usand. The sulfur isotope composition of the major minerals of the hydrothe rmal-sedimentary ores such as pyrite, sphalerite, and galena is similar. Th ere are no differences of the isotope composition of sulfur in the polystra tal stratabound ore bodies and along their lateral direction. A discreet di stribution of delta(34)S values across a thickness of the individual ore bo dies and ore rhythms was found. This is in agreement with a pulsation-rhyth mic deposition of sulfides from the near-bottom brines. Ores formed in the basin environments with highly reduced or oxygen-bearing conditions have si milar isotope-geochemical features. The marine water sulfates involved in t he dip-circulated ore-forming systems are considered to be the principal so urce of sulfur in this group of deposits.