Radium isotope geochemistry of thermal waters, Yellowstone National Park, Wyoming, USA
Radium isotope activities (226Ra, 228Ra, and 224Ra), chemical compositions, and sulfur isotope ratios in sulfate were determined for water samples from thermal areas in Yellowstone National Park, Wyoming. Activities of 226Ra in these waters range from <0.2 to 37.9 dpm/kg. Activity ratios of 228Ra226Ra">228Ra226Ra range from 0.26 to 14.2, and those of 224Ra228Ra">224Ra228Ra range from 0.73 to 3.1. Radium concentrations are inversely correlated with aquifer equilibration temperatures (estimated from dissolved silica concentrations), while[RaBa">RaBa]aq and 228Ra226Ra">228Ra226Ra activity ratios depend upon UBa">UBa and ThU">ThU ratios in aquifer rocks. Major controls on Ra concentration in Yellowstone thermal waters are inferred to be
1.
(1) barite saturation (at Morris Geyser Basin, Mammoth Hot Springs, and other northern areas) and
2.
(2) zeolitewater ion exchange (at Upper Geyser Basin). The data are consistent with a model in which
3.
(1) radium and barium are supplied to water by bulk dissolution of aquifer rock, and
4.
(2) chemical equilibration of water with rock is rapid relative to the 1602 year half-life of 226Ra. The 228Ra226Ra">228Ra226Ra activity ratios of the waters may in some cases reflect surface enrichments of 232Th and/or may indicate that α-recoil input of 228Ra is rapid relative to water-rock chemical equilibration. Activity ratios of 224Ra228Ra">224Ra228Ra indicate a nearly ubiquitous 224Ra excess that generally increases with decreasing pH. Near-surface (≤100 m) thermal water flow velocities at Mammoth Hot Springs are estimated from 224Ra228Ra">224Ra228Ra variation to be ≥ 1 m h−1.
Citation Information
Publication Year | 1993 |
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Title | Radium isotope geochemistry of thermal waters, Yellowstone National Park, Wyoming, USA |
DOI | 10.1016/0016-7037(93)90057-4 |
Authors | N.C. Sturchio, John K. Bohlke |
Publication Type | Article |
Publication Subtype | Journal Article |
Series Title | Geochimica et Cosmochimica Acta |
Index ID | 70231542 |
Record Source | USGS Publications Warehouse |