Variation in sericite composition from fracture zones within the Coso Hot Sprints geothermal system

Journal Article · Fri May 01 04:00:00 EDT 1987 · Geochim. Cosmochim. Acta; (United States)

DOI:https://doi.org/10.1016/0016-7037(87)90216-X· OSTI ID:6914157

Bishop, B P; Bird, D K

Two types of white micas are found in drill hole samples within the geothermal system at Coso Hot Springs. Low-permeability zones of the crystalline basement contain coarse-grained relict muscovite, whereas rock alteration near fracture zones at temperatures > 150/sup 0/C is characterized by abundant fine-grained sericite in association with secondary calcite and quartz and unaltered relict microcline. In this hydrothermal sericite there is an increase in interlayer K, octahedral Mg + Fe/sub total/ and tetrahedral Al with increasing temperature between approx. 215/sup 0/ to >250/sup 0/C. Thermodynamic activity of the Al/sub 2/Si/sub 4/O/sub 10/(OH)/sub 2/ component of sericites, calculated using site-mixing approximations of HELGESON and AAGAARD (1985), decreases with increasing temperature between approx. 215/sup 0/ and >250/sup 0/C. Although the compositions of hydrothermal sericites are a complex function of temperature, pressure and geothermal fluid composition, compositional relations observed at Coso together with published compositions of hydrothermal dioctahedral layer-silicates from the Salton Sea geothermal system demonstrates that elemental compositions of interlayer K and tetrahedral Al increase systematically with increasing temperature despite the dramatic differences in fluid compositions between these two geothermal systems. This suggests that the observed variations in interlayer and tetrahedral site occupancy is largely dependent on the enthalpy of hydrolysis reactions representing equilibrium between sericite solid solutions and the geothermal reservoir fluids.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 6914157
• Journal Information: Geochim. Cosmochim. Acta; (United States), Journal Name: Geochim. Cosmochim. Acta; (United States) Vol. 51:5; ISSN GCACA
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
152002* -- Geothermal Data & Theory-- Properties of Minerals & Rocks
58 GEOSCIENCES
580300 -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
580400 -- Geochemistry-- (-1989)
ACTIVATION ENERGY
CALIFORNIA
CHEMICAL COMPOSITION
CHEMISTRY
COSO HOT SPRINGS
ENERGY
FEDERAL REGION IX
GEOCHEMISTRY
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOTHERMAL SYSTEMS
HYDROTHERMAL ALTERATION
KINETICS
MICA
MOLECULAR STRUCTURE
NORTH AMERICA
REACTION KINETICS
STRUCTURAL CHEMICAL ANALYSIS
USA
VARIATIONS