Brennan Young, Utah State University
Geology
Thermal springs in northern Utah and southeastern Idaho mostly lie near active or inactive Basin-and-Range normal faults. They are dynamic systems, and the character of some has changed drastically since work as early as the 1980’s (Blackett and Wakefield, 2002; IDWR, 2001). We examined and sampled 60 thermal springs and most samples met criteria for cation geothermometers, or mathematical-geochemical tools used to estimate the maximum temperature of hydrothermal reservoirs. Of the 60 springs, 51 met criteria for the Na-K-Ca geothermometer and the remaining nine springs did not meet the criteria for the K-Mg, Na-K, Na-K-Ca, or Na-K-Ca-Mg cation geothermometers used in this project (Fournier and Truesdell, 1973; Fournier and Potter, 1979; Giggenbach, 1988). Of those 51 springs, only one is considered to be in partial equilibrium with the thermal reservoir, and estimates a reservoir temperature of 79°C (Giggenbach, 1988). Though the majority of springs exhibit a chemical signature of having mixed with shallow groundwater (Giggenbach, 1988), the Na-K-Ca geothermometer gives the most reliable results for springs in northern Utah and southeastern Idaho, but only for springs with surface temperatures exceeding 30°C and with greater than 1000 ppm total dissolved solids (TDS). Geothermometer results for these springs yield reservoir temperature estimates between 193 and 249°C.