Strontium in Pore Water from the Topopah Spring Tuff, Yucca Mountain, Nevada

摘要

Strontium isotope compositions of pore water from the welded Topopah Spring Tuff were measured in dry-drilledrncore either by leaching or by extraction by ultracentrifuge. Isotopic compositions of samples from the Cross Drift are withinrnthe range of compositions from three surface-based boreholes located along the Exploratory Studies Facility (ESF) tunnel. Anrnadvection-reaction model used to simulate the isotopic compositions of strontium in pore water indicates that water-rock interaction,rnprimarily in the nonwelded tuffs that overlie the welded Topopah Spring Tuff, is responsible for the narrow range ofrnisotopic compositions at the proposed repository level. Core samples from Niche 3566 in the ESF show a similarly narrowrnrange of strontium isotope compositions, indicating the same extent of water-rock interaction at this location and the samerntravel time as other areas within the proposed repository horizon.