Liquid-Vapour Partitioning of Trace-Elements in Boiling Hydrothermal Systems: Laser-Ablation ICPMS Data from Natural Fluid Inclusions

Abstract

Strong segregation of base metals between a hypersaline brine and a lower-salinity vapour has been observed by PIXE analysis of fluid inclusions (Heinrich et al., 1992), but some doubts remained whether the two inclusion types represent coexisting fluids. New micro-analytical data, from liquid and vapour inclusions trapped simultaneously in quartz in a variety of ore-deposits, now provide unambiguous and quantitative evidence for strong fractionation of a range of elements between coexisting fluids in 'boiling' hydrothermal systems. The thermodynamic explanation and the geological consequences of our observations are still speculative, but it is inevitable that the physical separation of brine and vapour has a profound influence on metal transport and ore deposition, especially for the behaviour of Cu, As and Au at the transition between 'porphyry' and 'epithermal' environments.