Characteristics[edit]
From Cox, (1986) US Geological Survey Bulletin 1693
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.
The upper portions of porphyry copper deposits may be subjected to supergene enrichment. This involves the metals in the upper portion being dissolved and carried down to below the water table, where they precipitate.
Porphyry copper deposits are typically mined by open-pit methods.