首页|Hydrothermal alteration of the surface volcanic rocks at the Acoculco geothermal field,Mexico:a multi-parametric approach
Hydrothermal alteration of the surface volcanic rocks at the Acoculco geothermal field,Mexico:a multi-parametric approach
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Hydrothermal alteration of the surface volcanic rocks at the Acoculco geothermal field,Mexico:a multi-parametric approach
The studies on hydrothermal alteration-induced effects in surface and subsurface rocks provide useful infor-mation in the characterization and exploitation of a geother-mal reservoir.Generally,these studies are based on tradi-tional,and reliable methods like petrography(primary and secondary minerals,and grade of alteration),and geochemis-try(mobility of elements,changes in mass and concentration of elements,and fluid inclusions).Recently,apart from these established methods,some methods based on the geochemi-cal(Chemical Index of Alteration,CIA;Weathering Index of Parkar,WIP;Loss on Ignition,LOI;and Sulfur,S)and rock magnetic properties(magnetic susceptibility,xlf;and percentage frequency-dependent susceptibility,xfd％)are also being applied in the identification of whether a rock is an altered or a fresh one.The Acoculco Geothermal Field(AGF),Mexico,is characterized by high temperature and very low permeability,and it is considered a promissory Enhanced Geothermal System.The following changes are observed in the rocks as a result of an increase in hydro-thermal alteration:(1)an increase in CIA,LOI,and S val-ues,and a decrease in WIP;(2)an increase in quartz and quartz polymorph minerals(silicification),and clay minerals(argillization);and(3)decrease in xlf values.At AGF,the most altered surface acid rocks are characterized by entirely quartz and its polymorphs,and clay minerals.The present study also indicates the applicability of the binary plots of major elements(felsic vs mafic component)and rock mag-netic parameters(xlf vs.xfd％).The rock with xfd％value of 2-10 and xlf value＜0.5 × 10-6 m3 kg-1 indicate the presence of single domain and stable single domain grains,which in turn suggests that it is an altered rock.These methods are simple to apply,rapid,reliable,and have the potential to become effective tools for the identification of hydrother-mally altered rocks during the initial stage of geothermal exploration.
Geothermal fieldsHydrothermal alterationSurface rocksMagnetic susceptibilityAlteration indices
America Yosiris García-Soto、Kailasa Pandarinath、E.Santoyo、Eduardo Gonzalez-Partida
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Instituto de Energías Renovables,Universidad Nacional Autónoma de México,Priv.Xochicalco s/no.,Col.Centro,Apartado Postal 34,62580 Temixco,Morelos,Mexico
Centro de Geociencias,UNAM,Apartado Postal 1-742,76001 Querétaro,Querétaro,Mexico
Geothermal fields Hydrothermal alteration Surface rocks Magnetic susceptibility Alteration indices
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