Oxygen and Hydrogen Isotope Geochemistry of Deep Basin Brines

Effects of potential geothermal development in the Corwin Springs Known Geothermal Resources Area, Montana, on the thermal features of Yellowstone National Park

“…In this model, water is in contact with Precambrian granitoids for relatively long periods during descent and lateral flow, and only in contact with limestones for shorter periods during ascent in the Gardiner fault. Isotopic exchange between water and silicate minerals is not likely at the low temperatures expected in this system (Truesdell and Hulston, 1980;Kharaka and Carothers, 1986). The differences in the 8D and 818O values of waters from the La Duke area and from Mammoth Hot Springs are an important indication that the two waters, even though both ultimately meteoric, are not isotopically related.…”

“…The minor 5D shifts (from a SD value of about -151) can be explained by mixing, as in the case of oxygen isotopes, or they could result from minor evaporation of recharge water before it percolates deep in the subsurface. They could result also from hydrogen exchange with clay minerals in the sedimentary section (Kharaka and Carothers, 1986).…”

“…The samples from La Duke Hot Spring and the CUT well plot on the meteoric water line, indicating that the water cannot be obtained by proportional mixing of a significant amount of thermal water from the Mammoth system with local meteoric water. The absence of measurable oxygen isotope shift in these waters also can be used to indicate a relatively short residence time of water in limestone aquifers, because long residence times in such aquifers at the calculated subsurface temperature of about 80°C would be expected to result in a more significant oxygen isotope shift (Clayton and others, 1966;Kharaka and Carothers, 1986;Plummer and others, 1990). The residence time in limestone aquifers could be short in this system if the recharge takes place in the Beartooth uplift.…”

“…Oxygen exchange with calcite in Paleozoic limestones resulting in heavier oxygen isotopes in water is a possibility because isotopic exchange can take place between water and calcite at relatively low (50° to 100°C) temperatures (Clayton and others, 1966;Kharaka and Carothers, 1986;Plummer and others, 1990). Alternatively, the oxygen shift could also result from mixing of a Mammoth meteoric water with the deep and unmodified thermal water from Norris Geyser Basin.…”

“…The 8D and 818O values of waters, especially when combined with the concentrations of conservative solutes (for example Cl) are the best geochbmical indicators of the origins, recharge locations, and flow paths of subsurface waters (for review articles and many references, see F-10 Truesdell and Hulston, 1980;Kharaka and Carothers, 1986). The stable isotopes of water are useful tools because the relations governing their distribution in present-day surface and shallow ground waters of an area (the local meteoric water) as well as their modifications in aquifers are reasonably well known.…”