Conditions for the Au–Ag Epithermal Mineralization in the Arykevaam Volcanic Field, Central Chukotka

Abstract

This article considers the conditions for the Au–Ag epithermal mineralization of the Arykevaam volcanic field (AVF) located in the middle of the Chukotka segment of the inner zone of the Okhotsk–Chukotka volcanic belt (OChVB). The results of thermo- and cryometric studies of fluid inclusions in quartz showed that epithermal mineralization was deposited by homogeneous hydrothermal fluids with low salt concentrations (0.3–1.5 wt % NaCl eq.), fluid densities of 0.77–0.83 g/cm3, at moderate temperatures, 267–229°C. In the fluid, among the cations, the main role is played by (g/kg H2O): K (1.8–10.2), Ca (4.7–12.9), and Na (3.7–5.8), and among the anions by SO42– (16.1–20.3), Cl (6.0–20.0), and $${\text{HCO}}_{{\text{3}}}^{ - }$$ (2.4–14.7). The main indicators of the fluid composition are CO2/ CH4 = 315–2818, Na/K = 0.37–3.18, and K/Rb = 324–743. According to water extracts, the real fluid salinity of the Arykevaam deposit (4.5–6.1 wt %) is significantly higher than that found by microthermometry, since the fluid is dominated by sulfates, not sodium chloride. The results allow us to attribute the mineralization studied here to the high sulfidation epithermal class.