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Fuchsite and other Cr-rich phyllosilicates in ultramafic enclaves from the Almadén mercury mining district, Spain

Published online by Cambridge University Press:  09 July 2018

D. Morata*
Affiliation:
Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla 13518, correo 21, Santiago de Chile
P. Higueras
Affiliation:
Departamento de Ingeniería Geológica y Minera, Universidad de Castilla-La Mancha, 13400 Almadén, Ciudad Real, Spain
S. Domínguez-Bella
Affiliation:
Departamento de Cristalografía y Mineralogía, Estratigrafía, Geodinámica y Petrología y Geoquímica, Universidad de Cá diz, 11510 Puerto Real, Cádiz, Spain
J. Parras
Affiliation:
Departamento de Ingeniería Geológica y Minera, Universidad de Castilla-La Mancha, 13400 Almadén, Ciudad Real, Spain
F. Velasco
Affiliation:
Departamento de Mineralogía y Petrología, Universidad del País Vasco, Apdo. 644, 48080 Bilbao, Spain
P. Aparicio
Affiliation:
Departamento de Cristalografía y Mineralogía y Química Agrícola, Facultad de Química, Universidad de Sevilla, Apdo. 553, 41041 Sevilla, Spain
*

Abstract

Fuchsite and other Cr-rich phyllosilicates, paragenetic with dolomite, are present in some ultramafic enclaves from the ‘frailesca’ rock (a lapilli- to block-size pyroclastic lithic-tuff), in the Almadén mercury mining district, Spain. Analyses (EMPA and TEM) of fuchsite and Cr-chlorite showed a relatively large range in levels of Cr2O3. Petrographic relationships between these phyllosilicates and primary relics of Cr-spinel crystals, as well as their high Cr content, indicate that these Cr-rich minerals originated from primary chromian spinels through an early hydrothermal alteration stage. The hydrothermal fluids accounting for this early alteration would be of relatively high temperature, high aCO2 and aK, and variable aNa/K. In a later alteration stage, fuchsite was partially or totally replaced by illite and Cr-illite, giving rise to an argillitic alteration.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2001

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