Isotope (d34S, d13C, d18O) Compositions of Disseminated Sulfide Mineralization in Igneous Rocks of the Dukat Ore Deposit (Northeastern Russia)

The paper discusses a study of variations in the S-34, C-13, O-18 compositions of disseminated sulfides and the carbonate phase, occurring in trace amounts in igneous rocks, which control the outlines of the unique Dukat Au-Ag deposit (northeastern Russia). The parameters obtained were compared with similar isotope parameters of ore assemblages of the same deposit. The S-34 values in sulfides and jarosite sampled in igneous rocks lie in a narrow interval (from -3.4 to + 3.6 parts per thousand), which is comparable with the interval of S-34 variations in sulfides from orebodies (from -4.5 to + 2.0 parts per thousand). Sulfur in pyrite of the early generation from K-Na leucogranites and pyrite from orebodies originated from the same source. Pyrite formed at late magmatic stages is characterized by a lighter sulfur isotope composition. Carbonate phases in igneous rocks of the Dukat ore deposit have low C-13 values (from -12.8 to -8.8 parts per thousand). Based on oxygen isotope composition, carbonates are subdivided into two groups: those in equilibrium with the silicate matrix of rocks at high temperatures and those with abnormally low O-18 values (from -0.8 to +0.9 parts per thousand). The data obtained can be described by a model that proposes that the formation of the sulfur isotope composition in sulfide and carbonate occurs in the process of thermochemical sulfate reduction (TSR) due to oxidation of organic carbon. Calculations show that the S-34 and C-13 values measured in rocks and ore assemblages of the Dukat ore deposit may have appeared due to abiogenic reduction of marine sulfate in a temperature range of 300-450 degrees C. Comparison ofates in orebodies may have been country (underlying) rocks and the fluid released from cooling intrusive bodies of K-Na leucogranites, in which about 80% CO2 is lost. the isotope parameters of carbonates from rocks and ore assemblages show that the source of carbon