Determination of mineralization temperature of the Aghyokhush group deposits within Chovdar ore field using fluid inclusion and δ34S isotop ratios

The geological structure of the Chovdar ore field, where the Aghyokhush group and Mereh deposits are located, consists of complex Middle and Upper Jurassic magmatic, metamorphic, and sedimentary rocks. The study below investigates the temperature and pressure conditions of mineralization in the Aghyokhush group and Chovdar deposits within the Chovdar ore field of the Lesser Caucasus. The study was carried out using fluid inclusion analysis and δ34S sulfur isotope data. Fluid inclusion petrography was conducted on barite mineral specimens from the Chovdar, Aghyokhush-1, -2, and -3, and Mereh deposits. As a result, four dominant inclusion types – monophase liquid (LH₂O), monophase vapor (VH₂O), and biphase liquid–vapor (LH₂O–VH₂O) – were identified in the barite specimens. These inclusions illustrate the presence of necking, decrepitation, and re-equilibration, which directly indicate pressure drops and boiling conditions during ore formation. Homogenization temperatures for barite-hosted inclusions range from 250–350 °C, with salinities of 5–8 wt.% NaCl equivalent, suggesting mineralization under high-sulfidation and strongly acidic (pH 2–4) conditions. Considering that barite formed late, either synchronously with ore generation or along faults after mineralization, it can be predicted that the Aghyokhush group deposits were formed by high-sulfide–bearing hydrothermal fluids. The study was conducted to determine the hydrothermal processes and ore formation conditions from isotope fractionation between sulfate and sulfide minerals at various temperatures. Complementary δ34S data from pyrite–barite pairs from the orebodies of the mentioned deposits indicate sulfur isotope values of ~2.9‰, which confirm hydrothermal fluid sources with consistent temperature conditions (approximately 340–400 °C) across all studied deposits. The results suggest that mineralization was driven by high-temperature, low-pressure fluids, likely derived from a common magmatic–hydrothermal system, with oxidation state and structural position influencing deposit variability.