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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


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