Reconnaissance δ¹³C and δ¹⁸O data from Trench 14, Busted Butte, and drill hole G-4, Yucca Mountain, Nevada test site

Trench 14 was excavated to investigate the extent of Quaternary movement on the Bow Ridge fault, a north-south structure on the east side of Yucca Mountain. The trench exposes calcite and opaline silica as fault breccia cements, veinlike fault fillings, and slope-parallel calcretes. Although the latter are clearly similar to calcretes of pedogenic origin, the cementing and fault-filling mineralization is enigmatic and has been variously attributed to deposition from ascending ground waters (warm or cool), from shallow-sourced (possibly perched) ground water, or from descending soil-zone waters ('recharge'). Preliminary δ¹³C and δ¹⁸O values of calcite from Trench 14, from sand-ramp calcretes and veinlike fault fillings at Busted Butte, and from drill core in the unsaturated zone of Yucca Mountain reveal some interesting trends and variations and provide some constraints on the temperature of calcite precipitation.