Petrography and phenocryst chemistry of volcanic units at Yucca Mountain, Nevada: A comparison of outcrop and drill hole samples
This report is a compilation of petrographic and mineral chemical data for stratigraphic units at Yucca Mountain. It supports a possible peer review of Yucca Mountain drill core by summarizing the available data in a form that allows comparison of stratigraphic units in drill holes with surface outcrops of the same units. Petrographic and mineral chemical data can be used in conjunction with other geologic and geophysical information to determine if stratigraphic relations in Yucca Mountain drill core are geologically reasonable and compare well with relations known from extensive surface studies. This compilation of petrographic and mineral chemical data is complete enough for most stratigraphic units to be used in a peer review of Yucca Mountain drill core. Additional data must be collected for a few units to complete the characterization. Rock units at Yucca Mountain have unique petrographic and mineral chemical characteristics that can be used to make accurate stratigraphic assignments in drill core samples. Stratigraphic units can be differentiated on the basis of petrographic characteristics such as total phenocryst abundances, relative proportions of phenocryst minerals, and type and abundances of mafic and accessory minerals. The mineral chemistry of phenocrysts is also an important means of differentiating among stratigraphic units, especially when used in conjunction with the petrographic data. Sanidine phenocrysts and plagioclase rims have narrow compositional ranges for most units and often have well-defined dominant compositions. Biotite compositions are useful for identifying groups of related units (e.g., Paintbrush Tuff Members vs Crater Flat Tuff Members) and for providing an important check on the consistency of the data. 21 refs., 12 figs., 2 tabs.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 60693
- Report Number(s):
- LA--11503-MS; ON: DE89010550
- Country of Publication:
- United States
- Language:
- English
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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
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