Uranium-isotope disequilibrium in brine reservoirs of the Castile Formation, northern Delaware Basin, southeastern New Mexico. I. Principles and methods
We evaluated uranium isotope activity ratios with respect to models for the origin of the brines in two brine reservoirs in the Castile Formation (ERDA No. 6 and WIPP No. 12). In Castile anhydrite, a completely closed water system that was continuously leaching Th-recoil-produced /sup 234/U from freshly exposed surfaces of fractured host rock would give rise to uranium 234/238 isotope activity ratio (..cap alpha..) values significantly higher than observed values. Therefore, the brine occurrences are not the result of continuous deformation. Similarly, a model assuming movement of intergranular Permian seawater into fractures was found inconsistent with observed uranium isotope systematics. The observed ..cap alpha..-values (95% confidence limits) of ERDA No. 6 (1.34 to 1.58) and WIPP No. 12 (1.74 to 2.54), used in conjunction with an inferred intial ..cap alpha../sub 0/ higher than observed values, allows calculation of reasonable finite minimum ages, involving no preferential leaching of /sup 234/U in the host rock. If the brine occurrences are inferred to have been connected at one time with a more extensive nearby hydrologic system, the Capitan limestone (..cap alpha../sub 0/ = 5.1), calculated minimum ages of isolation from that system are 700,000 to 880,000 yr for ERDA No. 6 and 360,000 to 610,000 yr for WIPP No. 12. These ranges in ages are the 95% confidence limits based on experimental determinations of ..cap alpha..-values. The ages thus derived may reflect an episode of structural deformation in the Pleistocene that allowed water to enter the resulting fractures. 16 references, 6 figures.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (USA); Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- AC04-76DP00789
- OSTI ID:
- 5261867
- Report Number(s):
- SAND-83-0144; ON: DE84007443
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
BRINES
ORIGIN
GROUND WATER
ISOTOPE RATIO
NEW MEXICO
SALT DEPOSITS
URANIUM 234
URANIUM 238
ANHYDRITE
ACTINIDE ISOTOPES
ACTINIDE NUCLEI
ALKALINE EARTH METAL COMPOUNDS
ALPHA DECAY RADIOISOTOPES
CALCIUM COMPOUNDS
CALCIUM SULFATES
EVEN-EVEN NUCLEI
FEDERAL REGION VI
GEOLOGIC DEPOSITS
HEAVY NUCLEI
HYDROGEN COMPOUNDS
ISOTOPES
MINERALS
NORTH AMERICA
NUCLEI
OXYGEN COMPOUNDS
RADIOISOTOPES
SULFATE MINERALS
SULFATES
SULFUR COMPOUNDS
URANIUM ISOTOPES
USA
WATER
YEARS LIVING RADIOISOTOPES
052002* - Nuclear Fuels- Waste Disposal & Storage
580400 - Geochemistry- (-1989)