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Title: Secondary mineral growth in fractures in the Miravalles geothermal system, Costa Rica

A mineralogical, fluid-chemical, and theoretical study of hydrothermal alteration in veins from drillcore from the Miravalles geothermal field, Costa Rica has revealed a complex history of mineral-fluid reaction which may be used to characterize changes in temperature and fluid composition with time. Mineralogical and mineral-chemical data are consistent with hydrothermal alteration in the temperature range 200{sup 0}-270{sup 0}C, with deeper portions of the system having undergone temperatures in excess of 300{sup 0}C. Thermodynamic calculations suggest that the observed alteration assemblage is not equilibrium with current well fluids, unless estimates of reservoir pH are incorrect. Fe-Al zoning of prehnite and epidote in veins is consistent with rapid, isothermal fluctuations in fluid composition at current reservoir temperatures, and may be due to changes in volatile content of the fluid due to tectonic activity.
Authors:
 [1] ; ;  [2] ;  [3]
  1. (Leeds Univ. (UK). Dept. of Earth Sciences)
  2. (British Geological Survey, Keyworth (UK). Fluid Processes Research Group)
  3. (Instituto Costarricense de Electricidad, San Jose (Costa Rica))
Publication Date:
OSTI Identifier:
5275655
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geothermics; (USA); Journal Volume: 18:1
Country of Publication:
United States
Language:
English
Subject:
15 GEOTHERMAL ENERGY; COSTA RICA; GEOTHERMAL SYSTEMS; MINERALOGY; RESERVOIR ROCK; THERMODYNAMICS; CHEMICAL COMPOSITION; CHEMICAL REACTIONS; ROCK-FLUID INTERACTIONS; CENTRAL AMERICA; DEVELOPING COUNTRIES; LATIN AMERICA 152003* -- Geothermal Data & Theory-- Rock-Water-Gas Interactions; 152001 -- Geothermal Data & Theory-- Properties of Aqueous Solutions