Geology of drill hole UE25p#1; a test hole into pre-Tertiary rocks near Yucca Mountain, southern Nevada

摘要

Yucca Mountain in southern Nye County, Nevada, has been proposed as a\udpotential site for the underground disposal of high-level nuclear waste. An\udexploratory drill hole designated UE25p#1 was drilled 3 km east of the proposed\udrepository site to investigate the geology and hydrology of the rocks\udthat underlie the Tertiary volcanic and sedimentary rock sequence forming\udYucca Mountain. Silurian dolomite assigned to the Roberts Mountain and Lone\udMountain Formations was intersected below the Tertiary section between a depth\udof approximately 1244 m (4080 ft) and the bottom of the drill hole at 1807 m\ud(5923 ft). These formations are part of an important regional carbonate aquifer\udin the deep ground-water system.\ud\udTertiary units deeper than 1139 m (3733 ft) in drill hole UE25p#1 are\udstratigraphically older than any units previously penetrated by drill holes at\udYucca Mountain. These units are, in ascending order, the tuff of Yucca\udFlat(?), an unnamed calcified ash-flow tuff, and a sequence of clastic deposits.\udThe upper part of the Tertiary sequence in drill hole UE25p#1 is similar\udto that found in other drill holes at Yucca Mountain.\ud\udThe Tertiary sequence is in fault contact with the Silurian rocks. This\udfault between Tertiary and Paleozoic rocks may correlate with the Fran Ridge\udfault, a steeply westward-dipping fault exposed approximately 0.5 km east of\udthe drill hole. Another fault intersects UE25p#1 at 873 m (2863 ft), but its\udsurface trace is concealed beneath the valley west of the Fran Ridge fault.\udThe Paintbrush Canyon fault, the trace of which passes less than 100 m\ud(330 ft) east of the drilling site, intersects drill hole UE25p#1 at a depth\udof approximately 78 m (255 ft). The drill hole apparently intersected the\udwest flank of a structural high of pre-Tertiary rocks, near the eastern edge\udof the Crater Flat structural depression.