Contribution of the paragenetic sequence of clay minerals to re-examination of the alteration zoning in the krafla geothermal system

David Escobedo; Patricia Patrier; Daniel Beaufort; Benoit Gibert; Léa Levy; Nathaniel Findling; Annette Mortensen

doi:10.3390/min11090935

Contribution of the paragenetic sequence of clay minerals to re-examination of the alteration zoning in the krafla geothermal system

David Escobedo, Patricia Patrier, Daniel Beaufort, Benoit Gibert, Léa Levy, Nathaniel Findling, Annette Mortensen

Research output: Contribution to journal › Article › peer-review

Abstract

This paper revisits the clay mineralogy of the “smectite” alteration zone in the Krafla geothermal field via the study of an exploratory well in which temperatures range from 40 °C to 215 °C. The clay alteration consists of several mineral assemblages superimposed in time and space, resulting from different stages of water-rock interaction. Trioctahedral clay minerals (chlorite, cor-rensite and smectite) are observed throughout the studied section. These minerals can form in nearly closed systems as replacements of groundmass minerals/glass after interactions with resi-dent and nearly stagnant fluids not far from chemical equilibrium (neutral to basic pH conditions) or from direct precipitation from geothermal fluids. They are locally superimposed by Al clay phases (smectite, illite/smectite and kaolinite), which result from intense leaching of the host rocks due to their interaction with low pH fluids under strong W/R ratios. The absence of mineralogical zoning is explained by the fact that hydrothermal alteration is strongly dependent on very recent hydrodynamics. The current fluid circulation generates trioctahedral clays at depth that cannot be distinguished from pervasive earlier alteration. The only easily detectable signature of current activity and the most relevant signature for geothermal exploration is the presence of Al dioctahedral phases since it indicates leaching and intense hydrothermal activity.

Original language	English
Article number	935
Journal	Minerals
Volume	11
Issue number	9
DOIs	https://doi.org/10.3390/min11090935
Publication status	Published - 2021 Sept
Externally published	Yes

Bibliographical note

Funding Information:
Acknowledgments: The authors thank the power company Landsvirkjun for providing access to core samples several times in very good conditions. L.L. thanks ÍSOR for the help with handling the samples and understanding their mineralogy, in particular Sigurdur Sveinn Jonsson. Christophe Nevado and Doriane Delmas are warmly thanked for the preparation of high-quality thin sections. This work was supported by a PhD grant from Paris Sciences et Lettres to Léa Lévy and the IMAGE FP7 EC and GEMex H2020 projects (grant agreements 608553 and 727550), as well as by a CNRS-INSU grant (TelluS program) attributed to the project AGERG. Fundings for travelling were provided by the PHC program JulesVerne, granted to Ecole Normale Supérieure and University of Iceland, by the Icelandic Centre for Research (Rannis) and the French Ministries of Foreign Affairs and International Development and of Education, Teaching and Research. The authors gratefully acknowledge also funding from the European Union (ERDF), ‘‘Region Nouvelle Aquitaine’’.

Funding Information:
Funding: This research was partly funded by TelluS-CESSUR (CNRS-INSU).

Publisher Copyright:
© 2021 by the authors. Licensee MDPI, Basel, Switzerland.

Subject classification (UKÄ)

Geotechnical Engineering

Free keywords

Clay minerals
Geothermal systems
Hydrothermal alteration
Krafla
Paragenetic model

Access to Document

10.3390/min11090935

Cite this

@article{223f5f5d91c0456da261504b46106904,

title = "Contribution of the paragenetic sequence of clay minerals to re-examination of the alteration zoning in the krafla geothermal system",

abstract = "This paper revisits the clay mineralogy of the “smectite” alteration zone in the Krafla geothermal field via the study of an exploratory well in which temperatures range from 40 °C to 215 °C. The clay alteration consists of several mineral assemblages superimposed in time and space, resulting from different stages of water-rock interaction. Trioctahedral clay minerals (chlorite, cor-rensite and smectite) are observed throughout the studied section. These minerals can form in nearly closed systems as replacements of groundmass minerals/glass after interactions with resi-dent and nearly stagnant fluids not far from chemical equilibrium (neutral to basic pH conditions) or from direct precipitation from geothermal fluids. They are locally superimposed by Al clay phases (smectite, illite/smectite and kaolinite), which result from intense leaching of the host rocks due to their interaction with low pH fluids under strong W/R ratios. The absence of mineralogical zoning is explained by the fact that hydrothermal alteration is strongly dependent on very recent hydrodynamics. The current fluid circulation generates trioctahedral clays at depth that cannot be distinguished from pervasive earlier alteration. The only easily detectable signature of current activity and the most relevant signature for geothermal exploration is the presence of Al dioctahedral phases since it indicates leaching and intense hydrothermal activity.",

keywords = "Clay minerals, Geothermal systems, Hydrothermal alteration, Krafla, Paragenetic model",

author = "David Escobedo and Patricia Patrier and Daniel Beaufort and Benoit Gibert and L{\'e}a Levy and Nathaniel Findling and Annette Mortensen",

note = "Funding Information: Acknowledgments: The authors thank the power company Landsvirkjun for providing access to core samples several times in very good conditions. L.L. thanks {\'I}SOR for the help with handling the samples and understanding their mineralogy, in particular Sigurdur Sveinn Jonsson. Christophe Nevado and Doriane Delmas are warmly thanked for the preparation of high-quality thin sections. This work was supported by a PhD grant from Paris Sciences et Lettres to L{\'e}a L{\'e}vy and the IMAGE FP7 EC and GEMex H2020 projects (grant agreements 608553 and 727550), as well as by a CNRS-INSU grant (TelluS program) attributed to the project AGERG. Fundings for travelling were provided by the PHC program JulesVerne, granted to Ecole Normale Sup{\'e}rieure and University of Iceland, by the Icelandic Centre for Research (Rannis) and the French Ministries of Foreign Affairs and International Development and of Education, Teaching and Research. The authors gratefully acknowledge also funding from the European Union (ERDF), {\textquoteleft}{\textquoteleft}Region Nouvelle Aquitaine{\textquoteright}{\textquoteright}. Funding Information: Funding: This research was partly funded by TelluS-CESSUR (CNRS-INSU). Publisher Copyright: {\textcopyright} 2021 by the authors. Licensee MDPI, Basel, Switzerland.",

year = "2021",

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language = "English",

volume = "11",

journal = "Minerals",

issn = "2075-163X",

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T1 - Contribution of the paragenetic sequence of clay minerals to re-examination of the alteration zoning in the krafla geothermal system

AU - Escobedo, David

AU - Patrier, Patricia

AU - Beaufort, Daniel

AU - Gibert, Benoit

AU - Levy, Léa

AU - Findling, Nathaniel

AU - Mortensen, Annette

N1 - Funding Information: Acknowledgments: The authors thank the power company Landsvirkjun for providing access to core samples several times in very good conditions. L.L. thanks ÍSOR for the help with handling the samples and understanding their mineralogy, in particular Sigurdur Sveinn Jonsson. Christophe Nevado and Doriane Delmas are warmly thanked for the preparation of high-quality thin sections. This work was supported by a PhD grant from Paris Sciences et Lettres to Léa Lévy and the IMAGE FP7 EC and GEMex H2020 projects (grant agreements 608553 and 727550), as well as by a CNRS-INSU grant (TelluS program) attributed to the project AGERG. Fundings for travelling were provided by the PHC program JulesVerne, granted to Ecole Normale Supérieure and University of Iceland, by the Icelandic Centre for Research (Rannis) and the French Ministries of Foreign Affairs and International Development and of Education, Teaching and Research. The authors gratefully acknowledge also funding from the European Union (ERDF), ‘‘Region Nouvelle Aquitaine’’. Funding Information: Funding: This research was partly funded by TelluS-CESSUR (CNRS-INSU). Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

PY - 2021/9

Y1 - 2021/9

N2 - This paper revisits the clay mineralogy of the “smectite” alteration zone in the Krafla geothermal field via the study of an exploratory well in which temperatures range from 40 °C to 215 °C. The clay alteration consists of several mineral assemblages superimposed in time and space, resulting from different stages of water-rock interaction. Trioctahedral clay minerals (chlorite, cor-rensite and smectite) are observed throughout the studied section. These minerals can form in nearly closed systems as replacements of groundmass minerals/glass after interactions with resi-dent and nearly stagnant fluids not far from chemical equilibrium (neutral to basic pH conditions) or from direct precipitation from geothermal fluids. They are locally superimposed by Al clay phases (smectite, illite/smectite and kaolinite), which result from intense leaching of the host rocks due to their interaction with low pH fluids under strong W/R ratios. The absence of mineralogical zoning is explained by the fact that hydrothermal alteration is strongly dependent on very recent hydrodynamics. The current fluid circulation generates trioctahedral clays at depth that cannot be distinguished from pervasive earlier alteration. The only easily detectable signature of current activity and the most relevant signature for geothermal exploration is the presence of Al dioctahedral phases since it indicates leaching and intense hydrothermal activity.

AB - This paper revisits the clay mineralogy of the “smectite” alteration zone in the Krafla geothermal field via the study of an exploratory well in which temperatures range from 40 °C to 215 °C. The clay alteration consists of several mineral assemblages superimposed in time and space, resulting from different stages of water-rock interaction. Trioctahedral clay minerals (chlorite, cor-rensite and smectite) are observed throughout the studied section. These minerals can form in nearly closed systems as replacements of groundmass minerals/glass after interactions with resi-dent and nearly stagnant fluids not far from chemical equilibrium (neutral to basic pH conditions) or from direct precipitation from geothermal fluids. They are locally superimposed by Al clay phases (smectite, illite/smectite and kaolinite), which result from intense leaching of the host rocks due to their interaction with low pH fluids under strong W/R ratios. The absence of mineralogical zoning is explained by the fact that hydrothermal alteration is strongly dependent on very recent hydrodynamics. The current fluid circulation generates trioctahedral clays at depth that cannot be distinguished from pervasive earlier alteration. The only easily detectable signature of current activity and the most relevant signature for geothermal exploration is the presence of Al dioctahedral phases since it indicates leaching and intense hydrothermal activity.

KW - Clay minerals

KW - Geothermal systems

KW - Hydrothermal alteration

KW - Krafla

KW - Paragenetic model

U2 - 10.3390/min11090935

DO - 10.3390/min11090935

M3 - Article

AN - SCOPUS:85113489310

SN - 2075-163X

VL - 11

JO - Minerals

JF - Minerals

IS - 9

M1 - 935

ER -

Contribution of the paragenetic sequence of clay minerals to re-examination of the alteration zoning in the krafla geothermal system

Abstract

Bibliographical note

Subject classification (UKÄ)

Free keywords

Access to Document

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Cite this