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Porphyry type Deposit

Chemical Process (Liquid-phase Growth) - Closed system under ground (Melt precipitation)

Required Geological Setting

Plutonic rocks

Associated metasomatic zones

Epidote-Actinolite zone, Illite-Chlorite zone


Disseminated-type deposit formed by hydrothermal fluid originated from Acidic (I-type Granite) or Neutral (Granodiorite, Diorite) I-type (magnetite-series) calc-alkaline magmatic activities. Deposits distribute in volcanic arcs such as volcanic island arcs at passive continental margins. Host rocks of deposits are granite porphyry or quartz porphyry intruded in shallow parts of crusts, and surrounding metasomatic rocks. Origin of hydrothermal fluid is magmatic water from magma for igneous host rocks, and mixture of magmatic and meteoric water for metasomatic host rocks. Oxidation zones of Cu are observed at the top of porphyry copper deposits. Porphyry copper deposits are usually low quality, typically 0.4-1.0 %. On the other hand, mining costs are low as its estimated amount is very large and the opencut mining technique can be applied. The porphyry type deposit is named after hosts of deposits, granite porphyry.

Mineral Assemblages

Chalcopyrite, Pyrite, Molybdenite, Magnetite, Chalcocite, Malachite, Chrysocolla, Atacamite

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