Open AccessPreliminary conceptual model for mineral evolution in Yucca Mountain
Author(s) -
C. J. Duffy
Publication year - 1993
Language(s) - English
Resource type - Reports
DOI - 10.2172/140106
Subject(s) - cristobalite , yucca , mineral , geology , groundwater , reaction rate , mineralogy , calcite , radioactive waste , geochemistry , chemistry , geotechnical engineering , quartz , paleontology , biochemistry , botany , organic chemistry , nuclear chemistry , biology , catalysis
A model is presented for mineral alteration in Yucca Mountain, Nevada, that suggests that the mineral transformations observed there are primarily controlled by the activity of aqueous silica. The rate of these reactions is related to the rate of evolution of the metastable silica polymorphs opal-CT and cristobalite assuming that a{sub SiO{sub 2(aq)}} is fixed at the equilibrium solubility of the most soluble silica polymorph present. The rate equations accurately predict the present depths of disappearance of opal-CT and cristobalite. The rate equations have also been used to predict the extent of future mineral alteration that may result from emplacement of a high-level nuclear waste repository in Yucca Mountain. Relatively small changes in mineralogy are predicted, but these predictions are based on the assumption that emplacement of a repository would not increase the pH of water in Yucca Mountain nor increase its carbonate content. Such changes may significantly increase mineral alteration. Some of the reactions currently occurring in Yucca Mountain consume H{sup +} and CO{sub 3}{sup 2{minus}}. Combining reaction rate models for these reactions with water chemistry data may make it possible to estimate water flux through the basal vitrophyre of the Topopah Spring Member and to help confirm the direction and rate of flow of groundwater in Yucca Mountain