In the Philippines, the bulk of copper production comes from the porphyry copper type. The original concept of porphyry copper is a uniform low-grade sulfide deposit wherein the sulfide minerals are disseminated discrete grains and veinlets throughout a large volume of rock, commonly a porphyry. In contrast, and reflective of what is termed as such in the Philippines, porphyry copper means a hypogene copper sulfide deposit in which the ore minerals are in disseminated grains or networks of veinlets within siliceous to intermediate intrusive bodies and their intruded rocks. This definition emphasizes the occurrence and genetic significance without consideration of the economic aspect and avoids the use of descriptive relative terms, such as low-grade, large, and big.

At least seven of these deposits in the Philippines are being mined and 16 are in the development or prospect stage. All are close to the axes of Tertiary geanticlines made up of Cretaceous to Tertiary metavolcanic and metasedimentary rocks. Most of the deposits are near prominent fault zones, especially where they branch or are intersected by other faults. The deposits are irregular in form, steeply dipping to flat, and localized near contacts of plutons and their intruded rocks. Ore minerals are chiefly chalcopyrite and to a less degree bornite. Magnetite, pyrite, molybdenite, gold, and silver, in some prospects, are recoverable as by-products.

Considering the present expansion programs of producing mines and the development of new mines which are in various stages of intensive exploration for this type of deposit, in the not too distant future mining of porphyry copper will constitute the biggest foreign-exchange earner among our major industries.

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