- journal_title：Geological Society of America Bulletin
- Contributor：B. J. SZABO ; T. K. KYSER
- Publisher：Geological Society of America
- Date：1990-
- Format：text/html
- Language：en
- Identifier：10.1130/0016-7606(1990)102<1714:AASICO>2.3.CO;2
- journal_abbrev：Geological Society of America Bulletin
- issn：0016-7606
- volume：102
- issue：12
- firstpage：1714
Stable-isotope compositions of fracture-and cavity-filling calcite from the unsaturated zone of three drill cores at Yucca Mountain Tertiary volcanic complex indicate that the water from which the minerals precipitated was probably meteoric in origin. A decrease in 18O in the calcite with depth is interpreted as being due to the increase in temperature in drill holes corresponding to an estimated average geothermal gradient of 34° per kilometer. A few of the calcite samples and all of the opal samples yielded uranium-series ages older than 400,000 yr, although most of the calcite samples yielded ages between 26,000 and 310,000 yr. The stable-isotope and uranium- series dates from precipitated calcite and opal of this reconnaissance study suggest a complex history of fluid movement through the volcanic pile, and episodes of fracture filling predominantly from meteoric water during at least the past 400,000 yr.