Geochemistry and Isotopes of Fluids from Sulphur Springs, Valles Caldera, New Mexico
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Journal Article: Geochemistry and Isotopes of Fluids from Sulphur Springs, Valles Caldera, New Mexico
AbstractDetailed geochemistry supported by geologic mapping has been used to investigate Sulphur Springs, an acid-sulfate hot spring system that issues from the western flank of the resurgent dome inside Valles Caldera. The most intense activity occurs at the intersection of faults offsetting caldera-fill deposits and post-caldera rhyolites. Three geothermal wells in the area have encountered pressures <1 MPa and temperatures of 200°C at depths of 600 to 1000 m. Hot spring and fumarole fluids may discharge at boiling temperatures with pH _ 1.0 and SO4 _8000 mg/l. These conditions cause argillic alterations throughout a large area.
>Non-condensible gases consist of roughly 99% CO2 with minor amounts of H2S, H2, and CH4. Empirical gas geothermometry suggests a deep reservoir temperature of 215 to 280°C. Comparison of 13C and 18O between CaCO3 from well cuttings and CO2 from fumarole steam indicates a fractionation temperature between 200 and 300°C by decarbonation of hydrothermally altered Paleozoic limestone and vein calcite in the reservoir rocks. Tritium concentrations obtained from steam condensed in a mudpot and deep reservoir fluids (Baca #13, _278°C) are 2.1 and 1.0 T.U. respectively, suggesting the steam originates from a reservoir whose water is mostly >50 yrs old. Deuterium contents of fumarole steam, deep reservoir fluid, and local meteoric water are practically identical even though 18O contents range through 4�, thus, precipitation on the resurgent dome of the caldera could recharge the hydrothermal system by slow percolation. From analysis of D and 18O values between fumarol steam and deep reservoir fluid, steam reaches the surface either (1) by vaporizing relatively shallow groundwater at 200°C or (2) by means of a two-stage boiling process through an intermediate level reservoir at roughly 200°C.
> Although many characteristics of known vapor-dominated geothermal systems are found at Sulphur Springs, fundamental differences exist in temperature and pressure of our postulated vapor-zone. We propose that the reservoir beneath Sulphur Springs is too small or too poorly confined to sustain a 'true' vapor-dominated system and that the Sulphur Springs system may be a 'dying' vapor-dominated system that has practically boiled itself dry.
- Fraser E. Goff, Jamie N. Gardner, Rosemary Vidale and Robert Charles
- Published Journal
- Journal of Volcanology and Geothermal Research, 1985
- Not Provided
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Fraser E. Goff,Jamie N. Gardner,Rosemary Vidale,Robert Charles. 1985. Geochemistry and Isotopes of Fluids from Sulphur Springs, Valles Caldera, New Mexico. Journal of Volcanology and Geothermal Research. 23(3-4):273-297.