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Chloritization in Proterozoic granite from the Äspö Laboratory, southeastern Sweden: record of hydrothermal alterations and implications for nuclear waste storage
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
2011 (English)In: Clay minerals, ISSN 0009-8558, Vol. 46, no 3, 495-513 p.Article in journal (Refereed) Published
Abstract [en]

Hydrothermal alteration of Proterozoic granitic rocks in the Aspo underground laboratory, southestern Sweden, resulted in the formation of chlorite with large variations in textural and chemical characteristics, which reflect differences in formation temperatures, fluid composition, and reaction mechanisms. The mineral assemblage associated with chlorite, including Ca-Al silicates (prehnite, pumpellyite, epidote, and titanite), Fe-oxides, calcite, albite and K-feldspar, suggests that chloritization occurred at temperatures of between 200-350 degrees C during various hydrothermal events primarily linked to magmatism and rock deformation. Petrographic and electron microprobe analyses revealed that chlorite replaced biotite, amphibole and magnetite, and hydrothermal chlorite phases filled fractures and vugs in the granitic rocks. While fracture-filling chlorite reduces fracture permeability, chloritization reactions in the host granite resulted in the formation of new localized microporosity that should thus be taken into consideration when evaluating the safety of the granitic basement rocks as a repository for nuclear waste. It is also important to take into account that similar alteration reactions may occur at the site of stored nuclear waste where temperatures in excess of 100 degrees C might be encountered.

Place, publisher, year, edition, pages
2011. Vol. 46, no 3, 495-513 p.
Keyword [en]
chloritization, chemical composition, hydrothermal, biotite granite, nuclear waste
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-160196DOI: 10.1180/claymin.2011.046.3.495ISI: 000295126200012OAI: oai:DiVA.org:uu-160196DiVA: diva2:448993
Available from: 2011-10-19 Created: 2011-10-18 Last updated: 2011-10-19Bibliographically approved

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