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Isotope geochemistry of thermal waters and gas discharges, Pueblo-Alvord Valley, Harney County, Oregon

Conference · · Geological Society of America, Abstracts with Programs; (United States)
OSTI ID:5163962
;  [1];  [2]
  1. Portland State Univ., OR (United States). Dept. of Geology
  2. Argonne National Lab., IL (United States)
Isotope of Sr, Ra, O, H, in thermal fluids and C, N, Ar and He in gas discharges were employed as tracers to determine reservoir lithology, fluid residence times for thermal areas in the Pueble-Alvord Valley, Harney County, Oregon. The [sup 87]Sr/[sup 86]Sr ratio in thermal fluids range from 0.70424 to 0.70478 and are not consistent with reservoir location in Steens or Pueblo Basalt. The Ra isotope ratio ranges from 0.17 to 1.14, lower ratios suggest U accumulation in the reservoir or interaction with limestone or gypsum. [delta][sup 13]C values are [minus]6.60 for two thermal areas and [minus]9.38 for a third. The former are consistent with atmospheric or volcanic CO[sub 2] sources, while the later may indicate a mantle contribution. [delta][sup 18]O and [delta]D ratios indicate meteoric water interaction with reservoir rocks. Tritium concentrations range from [minus]0.01 to 0.25 T.U. suggesting reservoir residence times greater than 35 years. Geochemical and isotope geothermometers estimate reservoir temperatures between 190 to 200 C. Thermal waters are classified as neutral to slightly alkaline Na-HCO[sub 3]. Meteoric waters from Steens Mountain are heated at depth within a reservoir that may include rhyolite and blocks or older crustal material. The fluids rise along frontal and basin faults to discharge at thermal springs.
OSTI ID:
5163962
Report Number(s):
CONF-9305259--
Conference Information:
Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
Country of Publication:
United States
Language:
English