Efectos de alteración hidrotermal y meteorización en vulcanitas del Grupo Aguacate, Costa Rica

The volcanic rocks of the Aguacate Group located at S and SW of the "Cordille-ra de Tilarán" represent an orogenic family principally composed by members of the tholeiític series and a few of the calc-alkaline series (sensu MIYASHIRO 1974). The main volcanic rocks of this Group are: uartz-...

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Autor Principal: Laguna Morales, Jorge
Formato: Artículo
Idioma: Español
Publicado: Universidad de Costa Rica 2011
Acceso en línea: http://revistas.ucr.ac.cr/index.php/geologica/article/view/10466
http://hdl.handle.net/10669/22614
Sumario: The volcanic rocks of the Aguacate Group located at S and SW of the "Cordille-ra de Tilarán" represent an orogenic family principally composed by members of the tholeiític series and a few of the calc-alkaline series (sensu MIYASHIRO 1974). The main volcanic rocks of this Group are: uartz-latiandesite, latiandesite, andesite and tuffite. Three types of wall rock alteration can be found in these rocks: 1. Strong propylitization in direct relation to pyrite fractures and in rocks in which the clay phases chlorite, beidellite, kaolinite and illite have been developed; 2. Intermediate to advanced argillic alteration with the subzones: a) kaolinite, b) kaolinite, aluníte, e) kaolinite, pyrophyllite d) beidellíte, illite/beidellite; e) kaolinite, cristobalite; 3. Incipient sericitic alteration with quartz and pyrite. 25%. Probably alunite is formed by the reaction of sulfuric acid with illite: KA13Si3010(OH)2 + 4H + 2504 KA13(304)2(OH) + 35i02 The theoretical standard free energy of chis reaetion is -42.0 Kcal/mol by The limits between the different types of alterations are not elearly defined. Secondary minerals e.g. chlorite, disordered kaolinite (fire clay) and beide-Ilite are also formed by reasons of weathering in zones which are not affected by hidrothermal alteration.