A large body of igneous rock, having distinct crystals in a relatively fine-grained base, that contains chalcopyrite and other sulfide minerals.
These deposits contain vast amounts of ore that averages a fraction of 1% copper by weight; although low-grade, the deposits are important because they can be worked on a large scale at low cost. Large porphyry copper deposits are worked in the southwestern U.S. (where molybdenum may be produced as a by-product), the Solomon Islands, Canada, Peru, Chile, Mexico, and elsewhere.