Preliminary study of lead isotopes in the carbonate-silica veins of Trench 14, Yucca Mountain, Nevada

Technical Report · Wed Dec 15 04:00:00 EST 1993

DOI:https://doi.org/10.2172/145235· OSTI ID:145235

Zartman, R E; Kwak, L M

The sub-vertical carbonate-silica veins filling the Bow Ridge Fault, where exposed in Trench 14 on the east side of Yucca Mountain, carry a lead isotopic signature that can be explained in terms of local sources. Two isotopically distinguishable--silicate and carbonate--fractions of lead are recognized within the vein system as well as in overlying surficial calcrete deposits. The acid-insoluble silicate fraction is contributed largely from the decomposing Miocene volcanic tuff, which forms the wall rock of the fault zone and is a ubiquitous component of the overlying soil. Lead contained in the silicate fraction approaches in isotopic composition that of the Miocene volcanic rocks of Yucca Mountain, but diverges from it in some samples by being more enriched in uranogenic isotopes. The carbonate fraction of lead in both vein and calcrete samples resides dominantly in the HCl- and CH{sub 3}COOH-soluble calcite. HCl evidently also attacks and removes lead from silicate phases, but the milder CH{sub 3}COOH dissolution procedure oftentimes identifies a significantly more radiogenic lead in the calcite. Wind-blown particulate matter brought to the area from Paleozoic and Late Proterozoic limestones in surrounding mountains may be the ultimate source of the calcite. Isotopically more uniform samples suggest that locally the basaltic ash and other volcanic rock have contributed most of the lead to both fractions of the vein system. An important finding of this study is that the data does not require the more exotic mechanisms or origins that have been proposed for the veins. Instead, the remarkably similar lead isotopic properties of the veins to those of the soil calcretes support their interpretation as a surficial, pedogenic phenomenon.

• Research Organization: Geological Survey, Denver, CO (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AI08-92NV10874
• OSTI ID: 145235
• Report Number(s): USGS-OFR--93-690; ON: DE94013976
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
CARBONATE MINERALS
CHEMICAL ANALYSIS
EXPERIMENTAL DATA
GEOCHEMISTRY
GEOLOGIC FAULTS
ISOTOPE RATIO
LEAD 204
LEAD 206
LEAD 208
ORIGIN
RADIOACTIVE WASTE FACILITIES
SILICATE MINERALS
SITE CHARACTERIZATION
THORIUM
URANIUM
YUCCA MOUNTAIN
Yucca Mountain Project