The depth of boiling in the epithermal environment: Comparison of different pressure regimes and implications to the design of fluid inclusion microthermometric studies

• Boiling of hydrothermal liquids is an important process of ore formation in intermediate-sulfidation epithermal deposits. • Boiling profiles for hydrothermal liquids of different salinities between surface conditions and their respective critical points are provided for several different pressure regimes. • Assumptions made on the prevailing pressure regime decisively influence the pressure-depth relationship and inferences made on the depth of ore zones below the paleosurface. • Paleodepth reconstructions are best conducted by recording the highest homogenization temperature encountered on liquid-rich fluid inclusion assemblages in a number of samples collected from different elevations within a given deposit or exploration project and enveloping the obtained temperature data with the hot hydrostatic boiling-point-to-depth profile for an aqueous solution of appropriate salinity. Boiling of hydrothermal liquids is an important process of ore formation in epithermal vein deposits formed within hundreds of meters below the paleowater table. This contribution provides boiling profiles for hydrothermal liquids in the H 2 O-NaCl model system between surface conditions and their respective critical points for several different pressure regimes. It is shown that assumptions made on the prevailing pressure regime decisively influence the pressure-depth relationship, which has implications to the interpretation of fluid inclusion data obtained from epithermal deposits. The results of this study demonstrate that paleodepth reconstructions are best conducted by recording the highest homogenization temperature encountered on liquid-rich fluid inclusion assemblages in a number of samples collected from different elevations within a given deposit or exploration project and enveloping the obtained temperature data with the hot hydrostatic boiling-point-to-depth profile for an aqueous solution of appropriate salinity. This contrasts with the practice of conducting microthermometric investigations on fluid inclusion assemblages that record boiling, or performing statistical analysis on large numbers of unconstrained microthermometric measurements.