Amount and Nature of Occluded Water in Bedded Salt, Palo Duro Basin, Texas
Bedded salt of the Permian San Andres Formation, Palo Duro Basin, Texas, is under consideration for the isolation of high-level nuclear waste. To represent the variety of salt types present, 150 large (250 to 500 g), intact samples of bedded halite from the San Andres Formation and other saltbearing units were selected and then analyzed by a standardized procedure. The halite fraction of the sample was dissolved in anhydrous methanol by continuous reflux Soxhlet extraction, and the water content was measured by Karl Fischer titration. All intergranular water and the water of fluid inclusions in halite are measured by this method; fluid inclusions in other minerals and the hydroxyl water of hydrous minerals are not. The mean water content of "pure" samples (more than 90 percent halite) is 0.4 weight percent. Samples that contain more than 10 percent clay or mudstone display a trend of increasing water content with increasing clastic material. Chaotic mudstone-halite samples have as much as 5 weight percent water; halite-cemented mudstone interlayers, common throughout the bedded salts, may have water-content values as high as 10 to 15 weight percent. No significant difference exists between the mean water-content values of "pure salt" from the upper San Andres, lower San Andres cycle 5, and lower San Andres cycle 4 salt units. Selected samples were heated under a partial vacuum to determine the amount of mobile intergranular water from the measured weight loss. The samples were then subjected to continuous reflux Soxhlet extraction and Karl Fischer titration to measure the remaining intergranular water and the water of fluid inclusions in halite. The fraction of total water present as mobile intergranular water thus determined is highly variable and not readily predicted from observed properties of the salt sample. The amount of water that would be affected by a high-level nuclear waste repository can be estimated if the volume of halite, the volume of clastic interlayers, and the amount and type of impurity in halite are known.
Fisher, R. S., 1985, Amount and Nature of Occluded Water in Bedded Salt, Palo Duro Basin, Texas: The University of Texas at Austin, Bureau of Economic Geology, Geological Circular 85-4, 27 p.
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The University of Texas at Austin, Bureau of Economic Geology