Evolution of Ore-Forming Fluids and Gold Deposition of the Sanakham Lode Gold Deposit, SW Laos: Constrains from Fluid Inclusions Study.

The Sanakham gold deposit is a newly discovered gold deposit in the Luang Prabang (Laos)–Loei (Thailand) metallogenic belt. It consists of a series of auriferous quartz-sulfide veins, which is distinguished from the regional known porphyry-related skarn and epithermal gold deposits. There are four mineralization stages identified in Sanakham, with native gold grains mainly occurring in stages II and III. Evolution of ore-forming fluids and gold deposition mechanisms in Sanakham are discussed based on fluid inclusion petrography, microthermometry, and Laser Raman spectroscopy. The original ore-forming fluids belong to a medium-high temperature (>345 °C) CH₄-rich CH₄–CO₂–NaCl–H₂O system. In stages II and III, the ore fluids evolve into a NaCl–H₂O–CO₂ ± CH₄ system characterized by medium temperature (~300 °C), medium salinity (~10 wt% NaCl eq.), and CO₂-rich (~10% mol). They might finally evolve into a NaCl–H₂O system with temperature decreasing and salinity increasing in stage IV. Two fluid immiscibility processes occurred in stages II and III, which created high-CH₄ & low-CO₂ and low-CH₄ & high-CO₂ end-members, and CO₂-poor and CO₂-rich endmembers, respectively. Gold-deposition events are suggested to be associated with the fluid immiscibility processes, with P–T conditions and depth of 236–65 MPa, 337–272 °C, and 8.7–6.5 km, respectively. [ABSTRACT FROM AUTHOR]