Fault-zone deformation in welded tuffs at Yucca Mountain, Nevada, USA

By contrast, Class B fault zones have unique mineralogies and microtextures relative to other Yucca Mountain fault zones. Most notable is the occurrence of distinctive jigsaw puzzle texture within fault core breccias, which consists of angular wall rock fragments floating in a coarsely crystalline secondary calcite cement matrix. The calcite cement constitutes more than 65% of the Class B fault zones. Comparisons with other occurrences of secondary minerals within open lithophysal cavities, which appear to have formed in unsaturated conditions, indicate that the secondary mineralization history at Yucca Mountain was complex and likely polygenetic. The age and origin of the secondary calcite minerals in the Class B fault zones remain undetermined.