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Marine-type upper oxidation zone

Chemical Process (Solution-Rock interaction) - Ground Surface (Marine)


Supergene enrichment zone, Supergene deposit

Required Geological Setting

Neogene and Quaternary sediments


Minerals deposited at vadoze zones above water tables by reduction reactions from components in the high-pH meteoric ground water produced at the Gossan zone near the ground surface. Mixing seawater with meteoric water, minerals contain halogen elements originated from seawater such as chlorine which are absent in the ordinal meteoric-type upper oxidation zone. Mineral species depends on reductive conditions of enclosing rock types and pH of ground waters at the deposition sites. The deeper depositon sites are, the more reductive. Thus mineral species associations depend on the depth of deposition sides. Supergene enrichment zones are composed of following zones in descending order: 1) Gossan zone, 2) Upper oxidation zone, 3) Lower oxidation zone, and 4) Secondary sulfide zone. The unaltered 5) Primary ore zone usually exists below the Secondary sulfide zone. The upper oxidation zone may distribute at laterally distant places from the Gossan zone as dissolved components in the meteoric water are transferred by ground water mixing seawater. Thickness of upper oxidation zones is up to 200-300 meters. Minerals species deposited in upper oxidation zones depends on enclosing rock types and pH at the deposition sites.

Mineral Assemblages

  • Atacamite
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