Detection of geothermal components in groundwaters of Dona Ana County, southern Rio Grande Rift, New Mexico
Chandler A. Swanberg
Dona Ana County is located in the southern part of New Mexico and occupies roughly 9,850 km astride the Rio Grande rift, an area of high regional heat flow and consider-able geothermal potential. Two known geothermal resource areas (Kilbourne Hole KG RA and Radium Springs KGRA) having a combined area of 141 km are located within the county.
Nearly 200 chemical analyses have been completed on waters collected from Dona Ana County. The majority of samples were collected from nonthermal groundwater wells although a few thermal wells and thermal and non-thermal springs are also represented. Thermal waters in the county are represented by Radium Springs (maximum reported temperature of 85oC), two thermal wells (43oC) at the Las Alturas Estates near Las Cruces, and possibly by a cold spring near San Diego Mountain which is located near and possibly associated with late Quaternary travertine deposits
There are two principle objectives to the present study. The first is to characterize the thermal waters of the county and then determine the extent to which any geothermal indicators can be recognized in the non-thermal groundwaters. The second objective is to assess the geothermal potential of Dona Ana County. On the basis of the data collected to date, the following conclusions can be drawn.
- Thermal waters in the county are associated with high silica and high sodium-potassium-calcium (Na-K-Ca) geochemical temperatures and high concentrations of fluoride and boron. These four parameters are useful in geothermal reconnaissance and can be used to detect the presence of, and possibly the migration of, geothermal fluids through normal ground-water aquifers.
- Maximum temperatures estimated by the Na-K-Ca geothermometer are in the 220-230oC range, a range well in excess of the often quoted 180oC limit for economic geothermal development.
- A prominent north-northwest trend of high geochemical temperatures passes through the county following the path of the major Valley fault (mapped on the basis of steep gravity gradients) and the geochemical temperatures decrease rapidly and systematically away from the fault. These data indicate that the Valley fault acts as a conduit for ascending geothermal fluids. Supporting this conclusion is the fact that the geochemical trend intersects the three occurrences of geothermal water noted above.
- Two segments of Dona Ana County are particularly promising for geothermal development. These include the bove mentioned geochemical trend and an extensive area entered around the Kilbourne Hole KG RA.
- The majority of samples collected from the northern art of the county fail to reveal any geothermal activity.
- Swanberg, Chandler A., 1975, Detection of geothermal components in groundwaters of Dona Ana County, southern Rio Grande Rift, New Mexico, in: Las Cruces Country, Seager, William R.; Clemons, Russell E.; Callender, Jonathan F., New Mexico Geological Society, Guidebook, 26th Field Conference, pp. 175-180.