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Smectite zone

Chemical Process (Alteration) - Open system under ground (Neutral metasomatism)

Correlated: Low-T zeolite facies


Bentonite Deposit, Argillized zone (Smectite)

Index Minerals


Required Geological Setting

Metasomatic rocks (Neutral)


Metasomatic zone formed by neutral hydrothermal fluid of 50-100 degree associated with Andesitic magma activities. This alteration is called smectization and is a part of argillization. Smectite zone may be associated with Hydrothermal Au-Ag deposits, Hot spring deposits or Hydrothermal deposits along faults. The water related to the alteration reaction of the smectite zone is meteoric water and/or magmatic water, and the water/rock ratio is more than a few tens times. It means that minerals were formed by reactions of the open system. On the other hand, the water related to the diagenesis is interstitial water in sediments, and the water/rock ratio is less than ten times. Minerals by diagenesis were formed by reactions of the closed system.

Smectite zone

Distribution of Smectite zones described in this site. Yellow lines are volcanic fronts.

Change of mineral assemblages

  • [ Appear ] Smectite

Mineral Assemblages

  • [ Felsic Rocks ] Smectite, Montmorillonite, (Calcite)
  • [ Mafic Rocks ] Smectite, Saponite, (Calcite)


Related Occurrences

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