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Illite-Chlorite zone

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

Correlated: Prehnite-Pumpellyite facies, Albite-Epidote-hornfels facies


Illite zone, Chlorite zone, Propylite zone, Sericite zone

Index Minerals

Illite, Chlorite, Adularia, Albite

Required Geological Setting

Metasomatic rocks (Neutral)


Metasomatic zone formed by neutral hydrothermal fluid of 220-300 degree associated with Andesitic magma activities. This alteration is called Illitization, Chloritization, or Sericitization, and is a part of Propylitization. Illite-Chlorite zone may be associated with Kuroko massive sulfide deposits, Backarc-type massive sulfide deposits, Cyprus-type massive sulfide deposits, Felsic-Siliclastic type massive sulfide deposits, Moderate-T hydrothermal deposits, or Porphyry copper deposits.

Illite-Chlorite zone

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

Change of mineral assemblages

  • [ Extinct ] Smectite/Illite, Smectite/Chlorite
  • [ Appear ] Illite, Chlorite, Adularia, Prehnite, Albite

Mineral Assemblages

  • [ Felsic Rocks ] Illite, Adularia, Quartz, Pyrite, Calcite, (Anhydrite)
  • [ Mafic Rocks ] Chlorite, Epidote, Prehnite, Albite, Calcite, (Pumpellyite, Dolomite)


Related Occurrences

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