The gold-and silver-rich base-metal sulfide ore deposits of the Central City district, Colorado, are arranged in well-defined concentric zones. A core of pyritequartz veins is surrounded by an outer zone of veins containing dominant galena and sphalerite in a gangue of quartz or, less commonly, rhombohedral carbonates, barite, or fluorite. In an intermediate area transitional veins contain pyrite, copper minerals, galena, and sphalerite. The transition from the core outward is marked also by systematic changes in gold and silver content, metal ratios, and mineral textures.

Temperatures of mineralization, as determined by sphalerite and fluid-inclusion thermometry, indicate that the veins...