干旱区生态环境知识资源中心(Arid): Pyritic ash-flow tuff, Yucca Mountain, Nevada -- A discussion

Arid

DOI	10.2172/240931
报告编号	DOE/NV/10461--T46
来源ID	OSTI_ID: 240931
	Pyritic ash-flow tuff, Yucca Mountain, Nevada -- A discussion
	Weiss, S.I.; Larson, L.T.; Noble, D.C. [Univ. of Nevada, Reno, NV (United States)]
英文摘要	Textural and mineralogic evidence exists for at least one episode of widespread hydrothermal alteration of volcanic rocks deep in Yucca Mountain, Nevada. Despite this evidence, Castor et al. infer that most of the pyrite found in tuffs at Yucca Mountain was introduced as ejecta (lithic fragments) incorporated during the eruptions of the tuffs, rather than by in-situ hydrothermal activity. Their conclusions appear to be based on their observation that most of the pyrite resides in unaltered to variably altered and veined lithic fragments, whereas pyrite-bearing veins are absent in the tuff matrix, titanomagnetite and mafic phenocrysts in the matrix are generally not replaced by pyrite, and feldspar phenocrysts in the pyritic tuff matrix are generally unaltered. Castor et al. dismiss the much smaller quantities of pyrite disseminated in the tuff matrix, including relatively rare pyritized hornblende and biotite grains, as xenolithic as well. The pyritic tuffs belong to large-volume, subalkaline rhyolite ash-flow units (ca. > 150 to 250 km{sup 3} each). The interpretation of Castor et al. has broad implications for the temperature, fO{sub 2} and fS{sub 2} of major ash flow eruptions. Pyrite origin also bears on the nature of past fluid flow and water-rock reactions at Yucca Mountain, which in turn are important factors in assessing the potential for currently undiscovered mineral resources in the area of the proposed nuclear waste repository. We have studied core and cuttings from the same drill holes studied by Castor et al., as well as other drill holes. It is our contention that the inconsistent lateral and stratigraphic distribution of the pyrite, textural features of the pyrite, and phase stability considerations are incompatible with the {open_quotes}lithic{close_quotes} origin of Castor et al., and are more reasonably explained by in-situ formation from hydrothermal fluids containing low, but geochemically significant, concentrations of reduced sulfur.
出版年	1994
报告类型	Technical Report
语种	英语
国家	美国
来源学科分类	05 NUCLEAR FUELS ; HIGH-LEVEL RADIOACTIVE WASTES ; UNDERGROUND DISPOSAL ; PYRITE ; ORIGIN ; TUFF ; GEOCHEMISTRY ; VOLCANIC ROCKS ; HYDROTHERMAL ALTERATION ; YUCCA MOUNTAIN ; SITE CHARACTERIZATION ; HORNBLENDE ; FLUID FLOW ; NEVADA ; PROGRESS REPORT
URL	http://www.osti.gov/scitech/servlets/purl/240931
资源类型	科技报告
条目标识符	http://119.78.100.177/qdio/handle/2XILL650/265969
推荐引用方式 GB/T 7714	Weiss, S.I.,Larson, L.T.,Noble, D.C. [Univ. of Nevada, Reno, NV . Pyritic ash-flow tuff, Yucca Mountain, Nevada -- A discussion,1994.