New evidence for a magmatic origin of some gases in the Geysers geothermal reservoir
The Geysers vapor-dominated geothermal reservoir is known to have a wide range of gas concentrations in steam (<100 to >75,000 ppmw), but the variations in gas compositions and the origin of the gases have been little studied. Low gas concentrations and steam isotopes similar to meteoric waters are found in the SE Geysers, but steam high in gas and HCI from a high temperature reservoir (HTR) in the NW Geysers has been thought to be related to metamorphic or magmatic brine. New analyses of noble gas isotopes show that the highest gas steam from the HTR has high {sup 3}He/{sup 4}He (8.3 Ra), and very low {sup 36}Ar and radiogenic {sup 40}Ar/{sup 4}He, indicating a strong magmatic component and essentially no atmospheric or crustal noble gases. Other samples from the HTR show various amounts of atmospheric dilution of the magmatic gas and lower HCI and total gas contents. The occurrence of steam in the NW Geysers highly enriched in heavy isotopes of oxygen and hydrogen supports the indications of remnant magmatic fluid: The existence of this fluid strongly suggests that the HTR was formed by rapid heating and catastrophic boiling resulting from injection of magma.
- Research Organization:
- Consultant, Menlo Park, CA; Lawrence Berkeley Laboratory, Berkeley, CA; Russian River Energy company, Santa Rosa, CA; International Institute for Geothermal Research, Pisa, IT
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 889231
- Report Number(s):
- SGP-TR-147-42
- Country of Publication:
- United States
- Language:
- English
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