Abstract

A fluid inclusion study of quartz from the Xa Loi gold deposit in Vinh Ô commune, Vinh Linh district, Quang Tri province, located in the Truong Son belt of central Vietnam, was conducted to elucidate the physicochemical conditions of the hydrothermal fluids responsible for gold mineralization. The fluid inclusions are dominated by liquid–vapor types, with homogenization temperatures ranging from 180°C to 370°C and clustering mainly between 240°C and 300°C, indicating medium- to high-temperature hydrothermal conditions consistent with deep metamorphic environments. The fluid salinities vary from 4.97 to 9.88 wt% NaCl equivalent (commonly 5–7 wt%), and the calculated fluid densities range from 1.28 to 1.35 g/cm³ (average 1.31 g/cm³), suggesting low- to medium-salinity, H₂ O-rich fluids formed under high-temperature and high-pressure conditions. The trapping pressures are estimated at 64.2–70.3 MPa, corresponding to depths of 4.66–4.95 km, while the pH values range from 6.22 to 6.33 (average 6.27), indicating a slightly neutral environment favorable for the transport and precipitation of gold together with sulfide minerals.

These characteristics indicate that the ore-forming fluids at Xa Loi exhibit typical features of orogenic gold systems, formed under medium-grade metamorphic conditions, high pressures, and intense compressional tectonics. The results not only shed light on the source and mechanisms of gold deposition at the Xa Loi deposit but also provide a scientific basis for guiding exploration for gold mineralization within the Truong Son belt.