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

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

Abstract
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.

Authors 
Hulen and J. B.  








Published 
Publisher Not Provided, 5/1/1978





DOI 
Not Provided
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Citation

Hulen, J. B.  . 5/1/1978. Geology and alteration of the Coso Geothermal Area, Inyo County, California. (!) : .


Related Geothermal Exploration Activities
Activities (1)


Areas (1)
  1. Coso Geothermal Area
Regions (0)