The Central City district in the Colorado Mineral Belt has produced over $100 million dollars of gold, silver, lead, zinc, copper and uranium since 1859 (Sims et al., 1963). Current activity, however, is limited to a few small mines.

Previous studies focused primarily on the pyritic-gold and base metal deposits that define a pattern of concentric zones in the district (Bastin and Hill, 1917; Sims and Barton, 1961, 1962; Sims et al., 1963; Moench and Drake, 1966). These deposits were concluded to have formed during Stages II and III of a complex hydrothermal system from a centralized, magmatic fluid source by irreversible adiabatic expansion and/or dilution via mixing with meteoric fluids. Localized deposits of enargite and telluride were simply considered specialized variants of the concentrically-zoned deposits (Sims and Barton, 1962) or isolated, late stage products of a specialized and meteorically-diluted magmatic fluid (Rice et al., 1985).

This study focuses on the geology of the Togo Mine, reopened in 1978, which suggests that boiling of the magmatic fluid may have precipitated the enargite- bearing deposits. The predominant factor influencing dilution or boiling may be related to the structural competency of the Precambrian host rocks and their behavior during Laramide intrusive activity.