Petrology of samples from drill holes USW H-3, H-4, and H-5, Yucca Mountain, Nevada
Hydrology drill holes USW H-3, H-4, and H-5, on the crest and eastern flank of southern Yucca Mountain, Nevada, penetrated a sequence of altered Tertiary pyroclastic rocks consisting of the Paintbrush Tuff, tuff of Calico Hills, and Crater Flat Tuff, in order of increasing age and depth. Multiple episodes of zeolitization are tentatively recognized in the upper Crater Flat Tuff and overlying units from petrologic study of drill bit cuttings and sidewall samples and from studies of samples from other drill holes. The earliest recognized episode was shallow burial diagenesis of Crater Flat Tuff and possibly tuff of Calico Hills before emplacement of the overlying Paintbrush Tuff. Heulandite-clinoptilolite and opal are the main alteration products. A second episode involved crystallization of heulandite and smectite during late-stage devitrification of vitrophyre in the Topopah Spring Member of the Paintbrush Tuff. A third episode of zeolitization, perhaps in part contemporaneous with the second, occurred approximately while the Paintbrush Tuff and older units were being displaced by tilting. Alteration products from this episode of burial diagenesis are clinoptilolite and minor smectite. Mordenite is an additional alteration product in some intervals. A nonlithophysal interval in the lower Topopah Spring tuff is under consideration for placement of a high-level nuclear waste repository. Heulandite and smectite in the altered vitrophyre directly beneath this interval could be the first highly sorptive minerals encountered by contaminated fluid escaping from a repository. Therefore, sorptive properties and thermochemical stability of these specific minerals should be further investigated. 50 references, 16 figures, 1 table.
- Research Organization:
- Los Alamos National Lab., NM (United States)
- DOE Contract Number:
- W-7405-ENG-36
- OSTI ID:
- 59174
- Report Number(s):
- LA--9706-MS; ON: DE84016010
- Country of Publication:
- United States
- Language:
- English
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