Petrography and mineral chemistry of units of the Topopah Spring, Calico Hills and Crater Flat tuffs, and older volcanic units, with emphasis on samples from drill hole USW G-1, Yucca Mountain, Nevada Test Site
This report contains a comprehensive set of petrographic and mineral chemical data for phenocrysts in volcanic units of Yucca Mountain drill hole USW G-1. This study provides a basis for petrographic comparison of units within Yucca Mountain and the Nevada Test Site (NTS), investigates several new petrographic techniques, and evaluates the usefulness of mineral chemical data obtained by electron microprobe analysis in correlating units. Correlation of these data with similar data for other drill holes of Yucca Mountain provides a primary means to evaluate the subsurface environment of the Waste Repository Site. The findings are applicable to programs that require an accurate knowledge of the subsurface geologic environment, particularly the Nevada Nuclear Waste Storage Investigations and Containment Programs at Los Alamos. Phenocryst modes provide a most effective means for subsurface correlation of volcanic units, but use of these data alone sometimes results in miscorrelations because substantial petrographic variations occur within some units. Phenocryst compositions, however, show little or no variation within each unit and they provide the most reliable data for correlation of volcanic units, particularly when combined with modal data. The modes and mineral compositions reflect the processes that were associated with eruption of the units, and so also greatly aid in the understanding of the subsurface geologic environment at USW G-1. Neither the phenocryst contents nor mineral compositions have been substantially affected by the wide range in alteration conditions that occur within USW G-1. Therefore, these findings are generally applicable to volcanic sequences of the NTS and elsewhere. 25 references, 14 figures, 22 tables.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 59175
- Report Number(s):
- LA--10003-MS; ON: DE84016048
- Country of Publication:
- United States
- Language:
- English
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