Geology and alteration of the Coso Geothermal Area, Inyo County, California

Technical Report · Mon May 01 04:00:00 EDT 1978

DOI:https://doi.org/10.2172/6279619· OSTI ID:6279619

Hulen, J. B.

Geology and alteration of the Coso geothermal area were mapped in conjunction with geophysical surveys and a deep drill test (CGEH-1) to facilitate selection of a follow-up drill site. The oldest rocks exposed at Coso are intermediate to mafic metamorphic rocks of uncertain age intruded by dikes and pods of quartz latite porphyry and felsite, and by a small stock of Late Cretaceous granite. These rocks are locally overlain by Late Cenozoic volcanic rocks, which include the domes, flows, and associated pyroclastic deposits of the Coso rhyolite dome field. Principal structures in the geothermal areas are older high-angle faults of uncertain displacement trending northwest, west-northwest, and east-northeast, and younger high-angle faults with a normal component of displacement trending north-northwest, north-northeast, and (subordinately) northeast. Active surface thermal phenomena and hydrothermal alteration are concentrated along the younger northerly-trending faults, especially where these faults intersect older structures. Deep thermal fluid flow at Coso will be controlled entirely by structural permeability developed in otherwise tight and impermeable host rocks. Neither geologic mapping nor deep drilling have revealed potential deep primary aquifers. Surface alteration at Coso is of three main types: (1) clay-opal-alunite alteration, (2) weak argillic alteration, and (3) stockwork calcite veins and veinlets, which are locally associated with calcareous sinter.

• Research Organization: Utah Univ., Salt Lake City (USA). Research Inst.
• OSTI ID: 6279619
• Report Number(s): IDO-1701-1
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
150201* -- Geology & Hydrology of Geothermal Systems-- USA-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
AQUIFERS
CALCITE
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CALIFORNIA
CARBON COMPOUNDS
CARBONATES
CENOZOIC ERA
CHALCOGENIDES
CLAYS
CRETACEOUS PERIOD
GEOLOGIC AGES
GEOLOGIC STRUCTURES
GEOLOGY
GEOTHERMAL FIELDS
GRANITES
HYDROTHERMAL ALTERATION
IGNEOUS ROCKS
INTRUSION
KGRA
MAPS
MESOZOIC ERA
MINERALIZATION
MINERALS
NORTH AMERICA
OXIDES
OXYGEN COMPOUNDS
PERMEABILITY
QUARTZ
ROCKS
SEDIMENTARY ROCKS
SILICON COMPOUNDS
SILICON OXIDES
USA
VOLCANIC ROCKS
WESTERN REGION