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 degrees 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 degrees 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 degrees C, and 8.7-6.5 km, respectively.