Porphyry copper deposit

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Porphyry copper deposits are copper orebodies which are associated with porphyritic intrusive rocks. The ore occurs as disseminations along hairline fractures as well as within larger veins, which often form a stockwork. The orebodies typically contain between 0.4 and 1 % copper with smaller amounts of other metals such as molybdenum, silver and gold. They are formed when large quantities of hydrothermal solutions carrying small quantities of metals pass through fractured rock within and around the intrusive and deposit the metals.

Porphyry copper deposits are the largest source of copper, and are found in North and South America, Europe, Asia, and Pacific islands. None are documented in Africa. The largest examples are found in the Andes in South America.

Characteristics of porphyry copper deposits include:

The orebodies are associated with multiple intrusions and dikes of diorite to quartz monzonite composition with porphyritic textures.
Breccia zones with angular or locally rounded fragments are commonly associated with the intrusives. The sulfide mineralization typically occurs between or within fragments.
The deposits typically have an outer epidote - chlorite mineral alteration zone.
A quartz - sericite alteration zone typically occurs closer to the center and may overprint.
A central potassic zone of secondary biotite and orthoclase alteration is commonly associated with most of the ore.
Fractures are often filled or coated by sulfides, or by quartz veins with sulfides. Closely spaced fractures of several orientations are usually associated with the highest grade ore.

Porphyry copper deposits are typically mined by open-pit methods.

1 Examples of porphyry copper deposits
- 1.1 Chile
- 1.2 United States
2 Porphyry-type ore deposits for metals other than copper
3 References

[edit] Examples of porphyry copper deposits

La Caridad, Sonora, Mexico
Ok Tedi, Papua New Guinea
Dizon, Phillipines

[edit] Chile

Chuquicamata
El Teniente

[edit] United States

[edit] Porphyry-type ore deposits for metals other than copper

Copper is not the only metal that occurs in porphyry deposits. There are also porphyry ore deposits mined primarily for molybdenum, many of which contain very little copper. Examples of porphyry molybdenum deposits are the Climax, Urad, and Henderson deposits in central Colorado, and the Questa deposit in northern New Mexico.

Some porphyry copper deposits in oceanic crust environments, such as those in the Phillipines, Indonesia, and Papua New Guinea, are sufficiently rich in gold that they are called copper-gold porphyry deposits.^[1]