Correlation of hydrothermal sericite composition with permeability and temperature, Coso Hot Springs geothermal field, Inyo County, California

Conference · Tue Jan 01 00:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6576180

Bishop, B P; Bird, D K

Petrographic and geochemical analyses of cuttings from six wells in the Coso Hot Springs geothermal field show a systematic variation in the occurrence, texture, and composition of sericite that can be correlated with high permeability production zones and temperature. The wells studied intersect rhyolitic dikes and sills in the fractured granitic and dioritic basement rocks which serve as the reservoir for the geothermal system. Low-permeability non-productive zones in the wells contain coarse-grained compositionally homogeneous primary muscovite. High-permeability production zones are characterized by abundant fine-grained hydrothermal sericite that exhibits a systematic increase in K and Al and decrease in Si with increasing temperature. Calculated activities of the muscovite and pyrophyllite components for the hydrothermal sericites increase and decrease, respectively, with increasing temperature. This trend is similar to that reported for geothermal systems at Roosevelt Hot Springs and the Salton Sea, although sericites from these systems are compositionally distinct from those at Coso. Computed distribution of aqueous species in the geothermal fluids were combined with activity phase diagrams accounting for hydrothermal sericite compositions to determine a pH of 6.1 for the geothermal fluids. These calculations suggest that hydrothermal sericites are in local equilibrium with the geothermal fluid, but primary muscovites in low permeability zones are metastable. Compositional data on hydrothermal sericite from active geothermal systems at Coso Hot Springs, Roosevelt Hot Springs, and the Salton Sea show that the mineral is sensitive to temperature and water/rock ratios and may be a useful indicator of high permeability zones within a geothermal field.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 6576180
• Report Number(s): CONF-8510489-
• Journal Information: Geol. Soc. Am., Abstr. Programs; (United States), Vol. 17; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
COSO HOT SPRINGS
VOLCANIC ROCKS
MUSCOVITE
GEOCHEMISTRY
PETROGRAPHY
TEMPERATURE EFFECTS
THERMODYNAMIC ACTIVITY
ACTIVATION ENERGY
CHEMICAL ANALYSIS
CHEMICAL COMPOSITION
GEOTHERMAL SYSTEMS
PERMEABILITY
TEXTURE
CALIFORNIA
CHEMISTRY
ENERGY
FEDERAL REGION IX
IGNEOUS ROCKS
MICA
MINERALS
NORTH AMERICA
ROCKS
SILICATE MINERALS
USA
580400* - Geochemistry- (-1989)