surface shows no evidence for the presence of boiling fluids, either in the fluid inclusion
record or mineral textures, it is unlikely that boiling occurred at greater depths in the vein
system. In this case, the quartz vein would not represent a high priority target for further
One of the locations where the temporal and spatial association of boiling and
precious metal deposition in epithermal deposits was first recognized was in the Finlandia
vein, Peru. There, Kamilli and Ohmoto (1977) identified seven distinct stages of
alteration and mineralization. Boiling, as evidenced by coexisting liquid-rich and vapor-
rich inclusions with variable phase ratios, was only recognized in the stage II bonanza
Ag-Au stage. These workers concluded that the precipitation of Ag-Au ore was caused by
boiling of hydrothermal fluids with salinities ranging from 0.2 to 13 wt. % NaCl
equivalent at temperatures between 250 ºC and 310 ºC (Kamilli and Ohmoto, 1977).
Similarly, in the National District in the Buckskin Mountains, Nevada, Vikre
(1985) reported that boiling did not occur in the early pre- Au-Ag stage (stage 1).
However, coexisting liquid-rich and vapor-rich inclusions with homogenization
temperatures ranging from 250 to 295ºC were observed in stages 2-4 that are associated
with Au and Ag mineralization. Importantly, the paleosurface at the time of
mineralization is still recognizable in this young system, and boiling is observed from a
depth of 2,000 feet all the way to the surface.
It is important to note that not all epithermal precious metals deposits show an
association between boiling and mineralization, as Albinson et al. (2001) have
documented for some Mexican silver deposits. Similarly, Casadevall and Ohmoto (1977)
found no evidence of boiling associated with precious metals deposition (stage 4) in the