Physical and stable-isotope evidence for formation of secondary calcite and silica in the unsaturated zone, Yucca Mountain, Nevada

Calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at Yucca Mountain, the potential site of a high-level radioactive waste repository. These secondary mineral deposits are heterogeneously distributed in the unsaturated zone (UZ) with fewer than 10% of possib...

Full description

Saved in:
Bibliographic Details
Published in:Applied geochemistry 2002-06, Vol.17 (6), p.735-750
Main Authors: Whelan, Joseph F, Paces, James B, Peterman, Zell E
Format: Article
Language:English
Subjects:
CALCITE
ISOTOPE RATIO
ISOTOPES
MANAGEMENT OF RADIOACTIVE WASTES, AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
NUCLEAR FUEL CYCLE AND FUEL MATERIALS
RADIOACTIVE WASTE FACILITIES
SATURATION LEVEL
SECONDARY CALCITE
SILICA
SITE CHARACTERIZATION
STABLE ISOTOPES
YUCCA MOUNTAIN
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Calcite and silica form coatings on fracture footwalls and cavity floors in the welded tuffs at Yucca Mountain, the potential site of a high-level radioactive waste repository. These secondary mineral deposits are heterogeneously distributed in the unsaturated zone (UZ) with fewer than 10% of possible depositional sites mineralized. The paragenetic sequence, compiled from deposits throughout the UZ, consists of an early-stage assemblage of calcite±fluorite±zeolites that is frequently capped by chalcedony±quartz. Intermediate- and late-stage deposits consist largely of calcite, commonly with opal on buried growth layers or outermost crystal faces of the calcite. Coatings on steep-dipping fractures usually are thin (⩽3 mm) with low-relief outer surfaces whereas shallow-dipping fractures and lithophysal cavities typically contain thicker, more coarsely crystalline deposits characterized by unusual thin, tabular calcite blades up to several cms in length. These blades may be capped with knobby or corniced overgrowths of late-stage calcite intergrown with opal. The observed textures in the fracture and cavity deposits are consistent with deposition from films of water fingering down fracture footwalls or drawn up faces of growing crystals by surface tension and evaporated at the crystal tips. Fluid inclusion studies have shown that most early-stage and some intermediate-stage calcite formed at temperatures of 35 to 85 °C. Calcite deposition during the past several million years appears to have been at temperatures
ISSN:0883-2927
1872-9134
DOI:10.1016/S0883-2927(02)00036-7