Том 61, № 1 (2019)

A reliable estimate is obtained for the gold mineralization age for the Malomyr deposit (eastern part of the Mongol–Okhotsk Fold Belt), one of the most well-known in the Russian Far East. The obtained data indicate that the age of the hydrothermal ore process that led to the formation of the Malomyr deposit can be estimated at ~134–130 Ma and the age of postore dikes is 110–104 Ma. At the same time, there are no data on magmatism manifesting itself within the studied region 134–130 Ma ago, making impossible to link the ore mineralization of the Malomyr deposit to magmatic processes. We think that dislocation processes accompanied by hydrothermal activity played a significant role in the mobilization, redistribution, and formation of the Malomyr deposit, which was supported by the results of structural studies. The first results of Rb-Sr and δ³⁴S studies indicate that the ore material came from both crustal and mantle sources.

The paper discusses a study of variations in the δ³⁴S, δ¹³C, δ¹⁸O 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 δ³⁴S values in sulfides and jarosite sampled in igneous rocks lie in a narrow interval (from −3.4 to + 3.6‰), which is comparable with the interval of δ³⁴S variations in sulfides from orebodies (from −4.5 to + 2.0‰). 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 δ¹³C values (from −12.8 to −8.8‰). 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 δ¹⁸O values (from −0.8 to +0.9‰). 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 δ³⁴S and δ¹³C 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°C. Comparison of the isotope parameters of carbonates from rocks and ore assemblages show that the source of carbonates 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.

Electron paramagnetic resonance (EPR) is used to study the composition and diffusion mobility of charge compensator ions in structural channels of quartz from the Darasun, Teremkinskoe, and Talatui gold fields of the Darasun ore field. The ion distribution features in quartz are evaluated based on their ability to participate in neutralizing the electrical charge of structural defects occurring in quartz. In accordance with this, the ion composition was assessed from the ratio of concentrations of Ti centers with different charge compensator ions, and their mobility was determined based on the formation rate of these centers under irradiation of quartz. The research shows the presence of two main types of charge compensator ions, H⁺ and Li⁺, in structural channels of quartz from the Darasun ore field. It was found that the diffusion mobility of H⁺ ions in channels are one to two orders of magnitude higher than that of Li⁺. There is no correlation between the composition of charge compensator ions and the fluid composition. Different ratios between concentrations of H⁺ and Li⁺ ions in structural channels of quartz from different deposits were established. The maximum concentrations of H⁺ ions and the minimum concentrations of Li⁺ ions are recorded in quartz from the Darasun ore field, and an inverse relation was recorded in quartz from the Talatui deposit. This can be explained by the migration of the gas component of fluid during ore genesis. It was shown that EPR can be applicable to quantitatively estimate the degree of dynamic recrystallization of quartz.