Boiling and dilution in the shallow portion of the Waiotapu geothermal system, New Zealand

Journal Article · Tue Oct 01 04:00:00 EDT 1991 · Geochimica et Cosmochimica Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(91)90442-8· OSTI ID:7117299

Hedenquist, J W ^[1]

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1. Geological Survey of Japan, Tsukuba (Japan)

The Waiotapu geothermal system is the largest in terms of surface extent and heat flow (17 km{sup 2} and 600 MW, respectively) of the 20 major geothermal systems in the Taupo Volcanic Zone, New Zealand. Thermal features comprise near-neutral pH chloride springs (often boiling), acid sulfate springs and mud pools, and mixed waters, the latter including both bicarbonate-chloride and acid sulfate-chloride springs. Comparison of measured and calculated surface chloride flux (the latter from measured heat flow and reservoir chloride concentrations) indicates that at least half of the deep chloride does not discharge at the surface, but flows laterally to the south at shallow depths, mixing with groundwater. There is chemical and stable isotope evidence from hot springs that cold groundwater also acts as a diluent at shallow levels, and very near the surface steam-heated acid sulfate waters mix with the upflow. Boiling of the deep chloride fluids prior to dilution results in the stabilization of K-feldspar. In contrast, dilution at shallower depths by the steam-heated waters (both CO{sub 2}-rich and acid sulfate) leads to the water compositions initially shifting to K-mica (and interstratified clay) stability, and to kaolinite stability with further dilution and temperature decrease. The composition and distribution of these fluids are consistent with alteration mineralogy and zonation observed in drill core. Although boiling occurs at deeper levels and up to the surface in the upflow zone at Waiotapu, mixing is also common and is the dominant process on the margin and in the near-surface portion of the system.

• OSTI ID: 7117299
• Journal Information: Geochimica et Cosmochimica Acta; (United States), Journal Name: Geochimica et Cosmochimica Acta; (United States) Vol. 55:10; ISSN GCACA; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
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ACID CARBONATES
AUSTRALASIA
BOILING
CHEMICAL COMPOSITION
CHEMISTRY
CHLORIDES
CHLORINE COMPOUNDS
COMPARATIVE EVALUATIONS
DEVELOPED COUNTRIES
DILUTION
EVALUATION
FLUIDS
GEOTHERMAL FIELDS
GEOTHERMAL FLUIDS
GEOTHERMOMETERS
GEOTHERMOMETRY
GROUND WATER
HALIDES
HALOGEN COMPOUNDS
HEAT FLOW
HOT SPRINGS
HYDROGEN COMPOUNDS
ISOTOPE RATIO
MEASURING INSTRUMENTS
MIXING
NEW ZEALAND
OXYGEN COMPOUNDS
PH VALUE
PHASE TRANSFORMATIONS
ROCK-FLUID INTERACTIONS
THERMAL SPRINGS
THERMAL WATERS
THERMOMETERS
WAIOTAPU GEOTHERMAL FIELD
WATER
WATER CHEMISTRY
WATER SPRINGS