Under the Department of Energy (DOE) National Geothermal Data System (NGDS) (Contract DE-EE0002850) Supplemental Data project to discover new geothermal data, the Arizona Geological Survey (AZGS) investigated the geochemical makeup of groundwater from select thermal springs and wells during late 2012 through 2013. In addition, the related geological context was investigated to evaluate potential groundwater transport mechanism(s) and heat source(s) relevant to geothermal energy production. Chemical analysis of thermal groundwater may be used to estimate subsurface temperatures by applying chemical geothermometry techniques, thus attempting to specify reservoir temperatures and to model possible sources of heat. An exploration program that integrates geochemical indicators of aquifer geometry and temperature with geology, geophysics, well targeting and well testing is likely to lower the cost of building sufficient confidence in resource conceptual models capable to commit to a generation capacity and plan well targets for development (Powell and Cumming, 2010). This report is intended to discuss the geochemistry and geology in relation to the select hot springs and wells sampled throughout Southern Arizona. This report presents the data and our interpretation to the extent of our limited understanding of geochemistry and complex factors that contribute to the geothermometry. It is meant to provide data for geothermal experts and others interested in pursuing additional interpretation. The geothermometry model devised by Tom Powell and William Cumming (Powell and Cumming, 2010) supports many of the common graphic analyses of water chemistry used to interpret hot spring and thermal well groundwater in geothermal exploration and development. The model provides geochemistry interpretative tools with proven value in exploring and characterizing the properties of both volcanic and forced-convection geothermal reservoirs. Cross-plots and ternary diagrams are generated from measured concentrations of chemical species using formulas based on equilibrium reactions and empirical relationships.

Hot (>30 degree C) water has been reported from the Safford area for at least seventy years. The most notable hot water occurrence, Indian Hot Springs, is located northwest of Safford near Fort Thomas. Indian Hot Springs, a health resort at the present time, includes several hot springs and an artesian well about 182 meters deep (Knechtel, 1938). Collective discharge of the springs and well is 320 gallons per minute (gpm) and the highest published discharge temperature is recorded at 48.3 degrees C (Knechtel, 1938). Nearly all wells deeper than 244 meters in the Safford area discharge artesian water. The deepest of these wells, the Mary Mack, was drilled in the NW, NE, Sec. 13, T6S, R.24E during 1929 and was completed to a depth of 1148 meters (Knechtel, 1938). The well encountered water flows at 495, 524, 676, 707, 978, and 1079 meters (Knechtel, 1938). In 1933, the well discharged 2500 gpm of 58.9 degrees C sodium chloride water containing 3251 parts per million (ppm) total dissolved solids (TDS) and 4.9 ppm fluorine (Knechtel, 1938). Present status of the well is not known because a field check of the described well location failed to find the well; but the well has probably been plugged and covered. (31 pages)