Hydrogeochemistry and geothermal potential of Montezuma Hot Springs, New Mexico
— F. Goff and C. Goff

The Montezuma Hot Springs discharge relatively dilute Na-Cl-HCO₃-SO₄ fluid having moderate silica contents (=80 ppm SiO₂) and amazingly high fluoride contents (up to 23 ppm F). There is no geochemical indication that the hot spring fluid is derived from a more concentrated, high-temperature (=150°C) reservoir fluid. Stable isotope relations show that the hot spring fluids are composed of local meteoric water. Tritium data show that the hot spring fluids are at least 50 to 70 years old based on a simple “piston-flow” model, and possibly several thousand years old based on a more complicated “wellmixed” model. The ³He/⁴He R/R_A value of hot spring fluid is only 0.083, indicating that there is virtually no primordial helium in the hot spring fluids and that there is no magmatic heat source for the underlying reservoir. The springs issue from crushed and fractured rocks at the intersection of the Montezuma Fault and the Rio Gallinas, and therefore fit a deep fault circulation conceptual model. Using a standard suite of chemical geothermometers, a reasonable estimate of the maximum reservoir temperature is about 115°C and a minimum reservoir temperature is about 90°C. Using a mass balance approach and a crude estimate of flow rate in the Rio Gallinas (September 1995), the estimated total discharge rate of end-member fluid from the Montezuma Hot Springs is 180 l/min (±30%).