Uranium-Series Geochronology of Hydrothermal Deposits, Dixie Valley, Nevada

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Conference Paper: Uranium-Series Geochronology of Hydrothermal Deposits, Dixie Valley, Nevada

Uranium-series dating of hydrothermal calcite, opal and quartz has been undertaken to help understand fluid transport and the timing of hydrothermal events associated with faulting in the Dixie Valley region. The Dixie Valley active geothermal system is located 160 km NE of Fallon in west-central Nevada within the Basin and Range tectonic province, and is fed by geothermal fluids arising from about 3000m depth. The fluid rises through faults and fractures associated with extension of the Stillwater fault system. A total of 14 samples comprised of travertine, or interlayered calcite, opal and quartz, were obtained from four deposits (groups 1-3, 5) along the valley. Samples were purified by handpicking, and where applicable, were separated into calcite, quartz or opal-rich fractions (20 separates in total). Samples were digested, spiked, and purified following standard methods. Uranium and some thorium measurements were obtained using a Micromass Sector54 TIMS equipped with a WARP filter. Many of the thorium measurements were obtained with a GV Isoprobe MC-ICP in the "soft extract" mode using the Cetac Aridus nebulizer. The Isoprobe provided greatly improved sensitivity and accuracy relative to the TIMS instrument. Uranium concentrations in quartz, opal and calcite separates range from 0.001 ppm to 1.227 ppm, and Th from 0.0001 to 3.278 ppm. Ages were obtained from isochron plots of calcite-opal/quartz pairs, or from a given group of samples assumed to share the same initial or detrital 230Th/238U and 234U/238U. The resulting preliminary ages are: Group 1: 5 ka; Group 2: 4 ka and 5 ka; Group 3: 97 ka; Group 5: 4.7 ka and 0.4 ka. The relatively young ages close to 5 ka for most samples from Groups 1, 2, and 5 are consistent with expectations based on the presence of active fumaroles that indicate a current heat source, as well as geologic observations for recent faulting that has provided conduits for fluid flow. The older age of 97 ka from group 3 travertine deposit is also consistent with expectations, as cold seeps and the absence of fumaroles indicate a lesser degree hydrothermal activity. These results show that U-series chronology is an important tool for understanding the longevity of hydrothermal systems and the time-scales of fluid-flow in the crust.

E Dixon, M Murrell, F Goff and N Goldstein

AGU Fall Meeting 2003; unknown; 2003/12/01

American Geophysical Union, 2003

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Internet link for Uranium-Series Geochronology of Hydrothermal Deposits, Dixie Valley, Nevada

E Dixon, M Murrell, F Goff, N Goldstein. 2003. Uranium-Series Geochronology of Hydrothermal Deposits, Dixie Valley, Nevada. In: AGU Fall Meeting 2003; 2003/12/01; unknown. unknown: American Geophysical Union; p. abstract #V51C-0312

Related Geothermal Exploration Activities
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  1. Dixie Valley Geothermal Area
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