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Clay mineral associations in the clay cap from the Cerro Pabellón blind geothermal system, Andean Cordillera, Northern Chile

Published online by Cambridge University Press:  14 June 2018

S.N. Maza ,
G. Collo ,
D. Morata ,
C. Lizana ,
E. Camus ,
M. Taussi ,
A. Renzulli ,
M. Mattioli ,
B. Godoy  and
B. Alvear
...Show all authors
S.N. Maza*
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
G. Collo
Affiliation:
Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales. Córdoba, Argentina. Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Centro de investigaciones en Ciencias de la Tierra, (CICTERRA). Córdoba, Argentina.
D. Morata
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
C. Lizana
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
E. Camus
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
M. Taussi
Affiliation:
Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino Carlo Bo, Via Cà le Suore, 2/4 –, 61029 Urbino, Italy.
A. Renzulli
Affiliation:
Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino Carlo Bo, Via Cà le Suore, 2/4 –, 61029 Urbino, Italy.
M. Mattioli
Affiliation:
Dipartimento di Scienze Pure e Applicate, Università degli Studi di Urbino Carlo Bo, Via Cà le Suore, 2/4 –, 61029 Urbino, Italy.
B. Godoy
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
B. Alvear
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
M. Pizarro
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile.
C. Ramírez
Affiliation:
ENEL Green Power Chile and Andean countries. Av. Presidente Riesco 5335, 14. Las Condes, Santiago, Chile.
G. Rivera
Affiliation:
Department of Geology and Andean Geothermal Center of Excellence (CEGA), Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Plaza Ercilla 803, Santiago, Chile. ENEL Green Power Chile and Andean countries. Av. Presidente Riesco 5335, 14. Las Condes, Santiago, Chile.
*
*E-mail: santiagomaz@gmail.com
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Abstract

The occurrence of smectite-illite and smectite-chlorite minerals series was studied along a thick clay cap (~300 m) drilled in the Cerro Pabellón geothermal field (northern Andes, Chile). X-ray diffraction (XRD) and scanning electronic microscopy (SEM) were used to characterize the alteration mineralogy and clay mineral assemblages and their changes with depth. Cerro Pabellón is a high-enthalpy blind geothermal system, with a reservoir zone from ~500 m to 2000 m depth, with temperatures of 200–250°C. Three main hydrothermal alteration zones were identified: (1) argillic; (2) sub-propylitic, and (3) propylitic, with variable amounts of smectite, illite-smectite, chlorite-smectite, mixed-layer chlorite-corrensite, illite and chlorite appearing in the groundmass and filling amygdales and veinlets. Chemical and XRD data of smectites, I-S and illites show, with some exceptions, a progressive illitization with depth. The evolution of I-S with depth, shows a sigmoidal variation in the percentage of illite layers, with the conversion of smectite to R1 I-S at ~180–185°C. These temperatures are greater than those reported for other similar geothermal fields and might indicate, at least in part, the efficiency of the clay cap in terms of restricting the circulation of hydrothermal fluids in low-permeability rocks. Our results highlight the importance of a better understanding of clay-mineral evolution in active geothermal systems, not only as a direct (or indirect) way to control temperature evolution, but also as a control on permeability/porosity efficiency of the clay cap.

Keywords

clay mineralsXRDSEMclay capgeothermicsCerro PabellónAndean CordilleraChile
Type
Article
Information
Clay Minerals , Volume 53 , Issue 2 , June 2018 , pp. 117 - 141
Copyright
Copyright © Mineralogical Society of Great Britain and Ireland 2018 

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Footnotes

This paper was presented during the session: ‘GG01-Clays in faults and fractures + MI-03 Clay mineral reaction progress in very low-grade temperature petrologic studies’ of the International Clay Conference 2017.

Guest Associate Editor: Blanca Bauluz

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