Manganese-oxide minerals in fractures of the Crater Flat Tuff in drill core USW G-4, Yucca Mountain, Nevada
The Crater Flat Tuff is almost entirely below the water table in drill hole USW G-4 at Yucca Mountain, Nevada. Manganese-oxide minerals from the Crater Flat Tuff in USW G-4 were studied using optical, scanning electron microscopic, electron microprobe, and x-ray powder diffraction methods to determine their distribution, mineralogy, and chemistry. Manganese-oxide minerals coat fractures in all three members of the Crater Flat Tuff (Prow Pass, Bullfrog, and Tram), but they are most abundant in fractures in the densely welded devitrified intervals of these members. The coatings are mostly of the cryptomelane/hollandite mineral group, but the chemistry of these coatings varies considerably. Some of the chemical variations, particularly the presence of calcium, sodium, and strontium, can be explained by admixture with todorokite, seen in some x-ray powder diffraction patterns. Other chemical variations, particularly between Ba and Pb, demonstrate that considerable substitution of Pb for Ba occurs in hollandite. Manganese-oxide coatings are common in the 10-m interval that produced 75% of the water pumped from USW G-4 in a flow survey in 1983. Their presence in water-producing zones suggests that manganese oxides may exert a significant chemical effect on groundwater beneath Yucca Mountain. In particular, the ability of the manganese oxides found at Yucca Mountain to be easily reduced suggests that they may affect the redox conditions of the groundwater and may oxidize dissolved or suspended species. Although the Mn oxides at Yucca Mountain have low exchange capacities, these minerals may retard the migration of some radionuclides, particularly the actinides, through scavenging and coprecipitation. 23 refs., 21 figs., 2 tabs.
- Research Organization:
- Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 137799
- Report Number(s):
- LA-11787-MS; ON: DE90014840; TRN: 90:029022
- Resource Relation:
- Other Information: PBD: Jul 1990
- Country of Publication:
- United States
- Language:
- English
Similar Records
Geology of the USW SD-7 drill hole Yucca Mountain, Nevada
Mineralogy, petrology and whole-rock chemistry data compilation for selected samples of Yucca Mountain tuffs; Yucca Mountain Site Characterization Project
Related Subjects
58 GEOSCIENCES
HIGH-LEVEL RADIOACTIVE WASTES
UNDERGROUND DISPOSAL
MANGANESE OXIDES
MINERALOGY
ENVIRONMENTAL IMPACTS
TUFF
STRATIGRAPHY
HOLLANDITE
CHEMICAL COMPOSITION
YUCCA MOUNTAIN
DRILL CORES
GEOLOGIC FRACTURES
WATER TABLES
CHEMISTRY
GROUND WATER
REDOX REACTIONS
RADIONUCLIDE MIGRATION
GEOLOGY
HYDROLOGY
GEOPHYSICAL SURVEYS
LITHOLOGY
ENVIRONMENTAL TRANSPORT
COMPILED DATA
Yucca Mountain Project