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Hydrothermal clay mineral formation in a biotite-granite in northern Switzerland

Published online by Cambridge University Press:  09 July 2018

Tj. Peters
Affiliation:
Mineralogisches-Petrographisches Institut, University of Berne, Balzerstrasse 1, Berne, Switzerland
B. Hofmann
Affiliation:
Mineralogisches-Petrographisches Institut, University of Berne, Balzerstrasse 1, Berne, Switzerland

Abstract

Clay minerals of several hydrothermally altered zones in a 1200-m biotite-granite core from a drillhole in northern Switzerland were studied microscopically, by XRD and by electron microprobe. The minerals principally affected by the hydrothermal alteration were plagioclase (An5-An20) and, to a lesser extent, biotite. Illite, regularly interstratified illite-smectite and dioctahedral chlorite-smectite, dioctahedral chlorite, trioctahedral chlorite and kaolinite were detected in the alteration products. Commonly, two or more clay minerals occurred together in pseudomorphs after plagioclase. The mineral chemistry of the clay minerals showed a predominance of the substitution KAl for Si and, to a lesser extent, MgSi for Al. Fluid-inclusion data and the absence of pure smectite and epidote indicated temperatures of ∼200°C for the fluid that caused this alteration.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1984

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