Estimation of underground temperatures from the silica content of water from hot springs and wet-steam wells

Solubility of quartz at depth is the major control on the amount of silica in solution in hot spring pools. Hot waters ascending rapidly to the surface become supersaturated with respect to quartz because of rapid cooling, separation of steam, and sluggish deposition of quartz and other crystalline SiO ~2~ phases. The silica content of boiling water discharged at the surface can be used to estimate underground temperature of last equilibrium with quartz, provided correction is made for steam forming during solution ascent. Using such correction, curves are presented showing dissolved silica measured in water discharged at the surface versus underground temperatures of last equilibrium with quartz. The method was applied to three wet-steam wells, and good agreement was obtained between the estimated and measured maximum temperature at depth.