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Morfologia y genesis de caolinitas en rocas silicificadas de la provincia de Avila (Espana)

Published online by Cambridge University Press:  09 July 2018

R. Marfil ,
A. Bustillo  and
MaC. Garcia Palacios
R. Marfil
Affiliation:
Dpto de Petrologia, Facultad de Ciencias Geologicas. Univ. Complutense. Madrid-3
A. Bustillo
Affiliation:
Dpto de Petrologia, Facultad de Ciencias Geologicas. Univ. Complutense. Madrid-3
MaC. Garcia Palacios
Affiliation:
Ibergesa. Juan Ramon Jiminez, 22, Madrid-16, Spain
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Resumen

Se realiza un estudio detallado de las distintas fases minerales (caolínicas y silíceas) que aparecen en rocas silicificadas tanto graniticas como sedimentarias de la provincia de Avila.

Las técnicas utilizadas (A.T.D., difracción de rayos X, microscopía electrónica de trasmisión y de barrido) permiten establecer una clasificación de estos minerales segun sus propiedades térmicas, parámetros cristaloquímicos, y morfologías identificadas al scaning.

Sa dá una interpretación genética a cada uno de los tipos de caolinitas encontrados (macrocaolinitas en acordeón, microcaolinitas en gusanillo y criptocaolinitas). Los dos primeros tipos pueden ser explicados por procesos conjuntos de alteración hidrotermal y ‘weathering’ de feldespatos y micas. El tercer tipo (criptocaolinitas) es de más difícil interpretación al aso-ciarse con ópalo C-T en diques que cortan a rocas granitoideas y otras veces al presentarse como matriz de areniscas sedimentarias.

Abstract

Abstract

Kaolinitic and siliceous minerals present in silicified granites and sedimentary rocks from the provice of Avila, Spain, have been studied by DTA, XRD and scanning and transmission electron microscopy. Three morphologically distinct types of kaolinite were recognized: (i) ‘spiral-like’ macrokaolinite, (ii) ‘vermicular’ microkaolinite and (iii) ‘cryptokaolinite’. The first two types formed by both hydrothermal alteration and weathering of feldspars and micas. The origin of the cryptokaolinite is obscure; it is associated with opal C-T in dykes which cross the granitic rocks and it is also found in the matrix of sedimentary sandstones.

Kurzreferat

Kurzreferat

Mit Hilfe von DTA, XRD, SEM und TEM wurden kaolinitsche und kieselsaurehaltige Minerale aus Graniten und Sedimenten der Provinz Avila, Spanien, untersucht. Es konnten 3 verschiedene Kaolinittypen bestimmt werden. (I) ‘spiralförmiger’ Makrokaolinit, (II) ‘vermiculitischer’ Mikrokaolinit, (III) ‘Kryptokaolinit’. Die beiden ersten Typen werden sowohl durch hydrothermale Umwandlungen als auch durch Verwitterung von Feldspäten und Glimmer gebildet. Die Bildung des ‘Kryptokaolinit’ ist dagegen unklar; er ist oft mit C-T Opal in Gängen vergesellschaftet, die die granitischen Gesteine durchziehen. Ebenso findet man den ‘Kryptokaolinit’ in der Matrix der sedimentären Sandsteine.

Résumé

Résumé

On a fait une étude en détail des differentes phases minéralogiques (kaoliniques et siliceuses) qu'on trouve dans de roches silicifiées, aussi bien granitiques que sédimentaires, en la province d'Avila.

Les techniques employées (ATD, diffraction de rayons X, microscopie électronique à transmission et à balayage) permettent d'établir une classification de ces minéraux d'après leurs propiétés thermiques, paramètres cristalochimiques et morphologies identifiées au microscope à balayage.

On en tire une interpretation génétique pour chacun des types de kaolinites trouvés (macrokaolinites en accordéon, microkaolinites en vermicules et cryptokaolinites. Les deux premiers types peuvent être expliqués par des processus conjoints d'altération hydrothermale et ‘weathering’ de feldspaths et de micas. Le troisième type a une interpretation plus difficile, car il est associé a de l'opale C-T parfois en dykes qui traversent des roches granitiques, et parfois comme matrice de roches sédimentaires.

Type
Research Article
Information
Clay Minerals , Volume 15 , Issue 3 , September 1980 , pp. 249 - 262
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1980

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