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Clays and Clay Minerals

, Volume 44, Issue 2, pp 244–256 | Cite as

Weathering of Chlorite in a Quartz-Chlorite Schist: I. Mineralogical and Chemical Changes

  • Takashi Murakami
  • Hiroshi Isobe
  • Tsutomu Sato
  • Toshihiko Ohnuki
Article

Abstract

The weathering of chlorite, one of the major minerals of the host rock in the uranium ore deposit at Koongarra, Australia, was examined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), electron microprobe analysis, and transmission electron microscopy (TEM). The conversion sequence of chlorite weathering is: (1) chlorite; (2) chlorite/vermiculite intergrade (showing XRD responses to various treatments intermediate between those of chlorite and vermiculite); (3) interstratified chlorite and vermiculite; (4) vermiculite; and (5) kaolinite. This sequence may be more simply expressed as chlorite ⤒ vermiculite ⤒ kaolinite. The weathering finally changed chlorite into sub-micrometer to micrometer sized Fe minerals and kaolinite. The transformation of chlorite to vermiculite is chemically characterized by an Fe and Mg loss with a slight decrease in the Al/Si ratio. Mg continues to be released throughout the weathering. Fe minerals formed through chlorite weathering are located between chlorite and vermiculite domains (a few u,m in size) at first, and then accumulated between grain boundaries, occasionally forming veins. The distribution of Fe minerals is suggestive of preferential pathways of water movement. The time-dependent nature of mineral alteration demonstrated in the present study must be taken into account for the quantitative estimation of radionuclide migration.

Key Words

Alteration Chlorite Kaolinite Uranium Ore Deposit Vermiculite Weathering 

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Copyright information

© The Clay Minerals Society 1996

Authors and Affiliations

  • Takashi Murakami
    • 1
  • Hiroshi Isobe
    • 2
  • Tsutomu Sato
    • 2
  • Toshihiko Ohnuki
    • 2
  1. 1.Department of Earth Sciences, Faculty of ScienceEhime UniversityMatsuyama, EhimeJapan
  2. 2.Department of Environmental Safety ResearchJapan Atomic Energy Research InstituteTokai, IbarakiJapan

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