Geology of drill hole UE18t and Area 18, Timber Mountain Caldera Moat, Nevada Test Site
Technical Report
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OSTI ID:5757426
Drill hole UE18t, located in the northeastern part of the Timber Mountain Caldera Moat (Area ft Nye County, Nevada, was sited to obtain chemical and physical data of the caldera-fill deposits and to extend knowledge of the geologic and hydrologic environment of the Nevada Test Site. Caldera-fill deposits in the area of subsidence related to eruption of the Rainier Mesa Member of the Timber Mountain Tuff (Tertiary) were penetrated to a depth of 1,635.0 ft (498.4 m), with the Rainier Mesa member extending below that depth to 2600.0 ft (792.5 m), the total depth of the drill hole. The caldera-fill deposits and the uppermost part of the Rainier Mesa are largely zeolitized and argillized tuffaceous rocks. The Ammonia Tanks Member from 945.0 to 1302.0 ft (288.0 to 396.8 m) is mostly unaltered welded tuff. Below 1889.7 ft (576.0 m), the Rainier Mesa is densely welded quartzo-feldspathic tuff with an average density of about 2.6 Mg/m/sup 3/, approaching that of granite. The static water level in UE18t has fluctuated within less than a foot (0.3 m) of 916 ft (279 m). The full suite of geophysical logs (caliper, density, resistivity, spontaneous potential, velocity, and neutron) from UE18t were interpreted and compared with physical properties measured on core. Cross-plot techniques were used to obtain additional properties of ash-flow tuffs below the water table. The log properties and cross plots indicate the quartzo-feldspathic tuffs of the Rainier Mesa Member have physical properties approaching those of granite. Correlation of log properties indicates the bedded tuffs above the Rainier Mesa Member and below the water table have very low permeability.
- Research Organization:
- Geological Survey, Denver, CO (USA); Los Alamos Scientific Lab., NM (USA)
- DOE Contract Number:
- AI08-76DP00474
- OSTI ID:
- 5757426
- Report Number(s):
- USGS-474-312; ON: DE82004718
- Country of Publication:
- United States
- Language:
- English
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