The Geysers-Clear Lake area, California: Thermal waters, mineralization, volcanism, and geothermal potential

Journal Article · · Economic Geology (plus the Bulletin of the Society of Economic Geologists); (United States)

DOI:https://doi.org/10.2113/gsecongeo.88.2.301· OSTI ID:5747217

Donnelly-Nolan, J M; Burns, M G ^[1]; Goff, F E ^[2]; Peters, E K ^[3]; Thompson, J M ^[1]

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1. U.S. Geological Survey, Menlo Park, CA (United States)
2. Los Alamos National Lab., NM (United States)
3. Harvard Univ., Cambridge, MA (United States)

Manifestations of a major thermal anomaly in the Geysers-Clear Lake area of northern California include the late Pliocene to Holocene Clear Lake Volcanics, The Geysers geothermal field, abundant thermal springs, and epithermal mercury and gold mineralization. The epithermal mineralization and thermal springs typically occur along high-angle faults within the broad San Andreas transform fault system that forms the western boundary of the North American plate in this area. Many of the waters of the region are nonmeteoric as defined by their isotopic signature. One type of isotopically shifted water emerges from or near Great Valley sequence rocks and is te most chloride rich. It is interpreted to be evolved connate in origin. A second type, evolved meteoric water, has moderate chloride contents, high boron contents, and high B/Cl ratios and is found locally in Franciscan rocks, notably at the Sulphur Bank mercury mine, where it probably results from near-closed-system, repeated boiling of meteoric water in host rocks that also contribute organic components to the water. Geothermal power production has peaked at The Geysers and pressure declines indicate significant depletion of the fluid resource. A deep water table of saline fluid has been postulated to be present under the steam field, but no chloride-rich water has been found at drillable depth. The authors propose that recently discovered, isotopically shifted steam in the northwest Geysers area indicates that presence not of deep connate water but rather of boiled-down, boron-rich Franciscan evolved meteoric water. This water is likely to be present in limited quantities and will not provide a significant hot water resource for geothermal power production at The Geysers field or from the main Clear Lake volcanic field.

• OSTI ID: 5747217
• Journal Information: Economic Geology (plus the Bulletin of the Society of Economic Geologists); (United States), Journal Name: Economic Geology (plus the Bulletin of the Society of Economic Geologists); (United States) Vol. 88:2; ISSN 0361-0128; ISSN ECGLAL
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150200* -- Geology & Hydrology of Geothermal Systems
152002 -- Geothermal Data & Theory-- Properties of Minerals & Rocks
152004 -- Geothermal Data & Theory-- Isotope & Trace Element Studies
CALIFORNIA
CHEMICAL COMPOSITION
CHEMISTRY
DEVELOPED COUNTRIES
ENERGY SYSTEMS
FLUIDS
GEOCHEMISTRY
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOLOGY
GEOTHERMAL FIELDS
GEOTHERMAL FLUIDS
GEOTHERMAL SYSTEMS
GEYSERS GEOTHERMAL FIELD
HYDROTHERMAL ALTERATION
HYDROTHERMAL SYSTEMS
ISOTOPE RATIO
MINERALIZATION
NORTH AMERICA
RESOURCE POTENTIAL
ROCK-FLUID INTERACTIONS
USA
VOLCANISM