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. 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 in the world and the largest examples occur 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.