Ayakhta gold-quartz deposit (Yenisei Ridge): formation conditions and source of fluids

Relevance. The need to establish the parameters of ore-bearing fluids of the Ayakhta gold deposit, one of the standard and large objects in the Yenisei Ridge. The data obtained can be used to develop a holistic model of gold mineralization in the region. Aim. To determine the physicochemical conditions for the formation of quartz vein zones and ore-bearing fluids source. Methods. We analyzed the ore minerals composition by micro-X-ray spectral analysis, determined the temperatures of phase transitions in fluid inclusions using the microthermometry method, determined the individual fluid inclusions composition by Raman spectroscopy. The fluid bulk composition was analyzed by gas chromatography-mass spectrometry (GC-MS). To establish the source of the fluid, we used isotopes of sulfur (δ34S) sulfides and carbon dioxide (δ13C) in fluid inclusions in quartz. Results and conclusions. We established that the gold-quartz vein zones formation occurred under medium temperature conditions (121–424°C) with significant pressure fluctuations (0.5–1.5 kbar). The fluid salinity was moderate (up to 25.5 wt %, NaCl-eq.). Using the GC-MS method, we detected from 178 to 286 compounds in the ore-bearing fluid, H2O and CO2 predominate among them. The share of hydrocarbons, their derivatives, S-, N- and halogenated compounds in total accounts for 7.4–22.6 rel. %. We assume that organic compounds were directly involved in the enrichment of quartz veins with gold mineralization. The isotope composition values of sulfur (+6.6…+9.5 ‰) and carbon from fluid inclusions in quartz (–12.5…–21.9 ‰) indicate a metamorphic-crustal source of fluids.