Hydrology and Chemistry of Thermal Waters Near Wells, Nevada

Abstract

Anomalously warm water in shallow wells and surface springs is found in and around the town of Wells, Nevada. The geology of the Wells area is dominated by Paleozoic and Miocene sedimentary rocks which are cut by high angle normal faults. Thermal springs are associated with the normal faults, whereas thermal water from wells is the result of upward vertical fluid infiltration through the porous, Miocene lacustrine sedimentary rocks and Quaternary alluvium. Temperature logs from a nearby oil exploration well show locally high geothermal gradients (> 50° C/km). Analysis of static water heads indicates that vertical flow is greater than or equal to horizontal flow in low-lying areas near the town of Wells. Solution of the advection-diffusion equation using temperature data from the upper portion of the oil well suggests upward flow velocities of approximately 2–10 m/yr. Cold waters have a mixed cation-bicarbonate chemistry whereas thermal waters are dominantly (Na + K)-bicarbonate. Chemical geothermometers indicate fluid circulation to depths between 1–2 km. Deuterium and oxygen-18 analyses have considerable variability, with modest deviations from the global meteoric water line. The occurrence of deuterium as light as – 145% suggests significant recharge to the hydrothermal system from very high elevations or water which has had a long subsurface residence time and is recording the signal of a cooler climate.