Characterization of fault-filling deposits in the vicinity of Yucca Mountain, Nevada

The origin of calcite and opaline silica vein-like deposits that infill faults and fractures in the vicinity of Yucca Mountain has been the center of considerable controversy because the area is being characterized geologically as a possible site for the nation's first high-level nuclear waste repository. Various proposed modes of origin have differing implications for the performance of a geologic repository. A number of lines of evidence now converge and show that upwelling of ground water, either catastrophically in response to tectonic forces or passively in response to a regional rise in water-table elevation, was not responsible for the vein-like deposits. Field observations and mineralogic, petrographic, and paleontologic data all suggest an origin related to soil-forming processes. Isotopic data for carbon, oxygen, strontium, uranium, and lead all support this conclusion and further rule out involvement of any of the local aquifers. (author)