Mineralogic, petrologic, and geochemical studies of the volcanic rocks at Yucca Mountain, Nevada, for high-level waste disposal

Studies of mineralogy, petrology, and geochemistry at a candidate high-level waste repository site must address three primary concerns: (a) possible future geologic events that can compromise waste isolation, (b) possible conflicting site uses, and (c) the natural ability of the site to contain radionuclide waste. Data are being collected to address these concerns for a potential unsaturated repository location at Yucca Mountain, Nevada. The major tuff units underlying the potential repository area at Yucca Mountain extend upward from the thick (∼450 to 700 m) Crater Flat Tuff (∼13.9 million years old), through the informally named tuffs of Calico Hills (∼25 to 110 m, 13.8 million years old) into the Paintbrush Tuff (∼410 to 425 m, 13.4 to 12.9 million years old). The candidate host rock for a high-level waste repository is within the devitrified Topopah Spring Member of the Paintbrush Tuff. This entire sequence has been faulted and tilted to the east and is covered by the Rainier Mesa Member of the Timber Mountain Tuff (11.6 million years old)