The dominant rocks exposed at Goldfield are rhyolites and latite tuffs, overlain by younger andesitic rocks of Miocene age. Alteration was controlled by pre-existing faults and fractures, some of which are associated with a buried ring fracture system. Post-mineralization rocks include basalts, tuffs, and sedimentary rocks. Rocks in the Cuprite area include Cambrian siltstone, sandstone, and limestone and Tertiary volcanic rocks, including tuffs and basalt. About 7 million years ago, the rocks were subjected to acid-sulfate alteration, that chemically changed the rocks and likely deposited precious metals.
Hydrothermal alteration forms three mappable units.
Figure 2 Figure 3 Figures 2 and 3 cover the 30 km by 35 km area within which the Goldfield and Cuprite districts lie. As labeled in Figure 2, the Goldfield district is in the upper center of the images, and Cuprite is the bright area in the bottom center. Cuprite stands out in light blue due to the prevalence of bleached, altered rocks. Alteration at Goldfield is less obvious, but might be distinguished as salmon and dark yellow colored outcrops. Yellow areas combine minerals with both absorption features.