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Sunnyside, Colorado, epithermal deposit. They did, however, report boiling during the

latest stage 6 that contains no precious metal mineralization.

During the past half century several workers have studied fluid inclusions in the

Guanajuato Mining District (GMD) (Table 1). One of the earliest studies, by Wilson et al.

(1950), focused on mines in the central part of GMD (Fig. 2). Thirty samples containing

quartz crystals from the Rayas mine and the Cata mine showed homogenization

temperatures ranging from 215 to 299 ºC, with an average of 254 ºC and a mean of 257

ºC. These workers did not comment on whether the samples contained both liquid-rich

and vapor-rich inclusions in the same assemblages.

Gross (1975) reported fluid inclusion homogenization temperatures from several

samples collected along the Veta Madre and adjacent Sierra vein system (Fig. 2).

Temperatures ranged from about 260 to 330°C and showed a systematic increase with

depth. For example, the temperature at an elevation of 1700 m was 320°C and dropped to

260°C at 2400 m along the Veta Madre. As with the earlier work by Wilson et al. (1950),

Gross (1975) did not indicate whether the samples contained both liquid-rich and vapor-

rich inclusions in the same assemblages.

The most detailed fluid inclusion study in the GMD and the first that relates

boiling and precipitation of precious metals was conducted by Buchanan (1979), whose

research focused on the Las Torres mine and the deepest levels of the Rayas mine (1705

meter level) (Fig. 2). In both mines, coexisting liquid-rich and vapor-rich inclusions

indicated that boiling occurred during precious metal mineralization. In the Las Torres

mine, a correlation was observed between silver sulfide deposition, high abundance of

fluid inclusions with homogenization temperatures ranging from 231 to over 360 ºC, and

4

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