Chloritization in proterozoic granite from Äspö Laboratory, southeastern Sweden: Record of hydrothermal alterations and implications for nuclear waste storage

S. Morad*, M. Sirat, M. A K El-Ghali, H. Mansurbeg

*Corresponding author for this work

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Hydrothermal alteration of Proterozoic granitic rocks in the Äspö 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°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°C might be encountered.

Original languageEnglish
Pages (from-to)495-513
Number of pages19
JournalClay Minerals
Volume46
Issue number3
DOIs
Publication statusPublished - 2011

Keywords

  • BIOTITE GRANITE
  • CHEMICAL COMPOSITION
  • CHLORITIZATION
  • HYDROTHERMAL
  • NUCLEAR WASTE

ASJC Scopus subject areas

  • Geochemistry and Petrology

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