Copper and Molybdenum Deposits in the United States Copper and molybdenum resources were not recognized as valuable commodities until economic needs demanded the collection and processing of these minerals in large amounts. The most expansive deposits of copper and molybdenum occur in massive low grade ores and are found in intrusive porphyry formations, although many smaller sized but higher grade ores are located in non-porphyry areas. The nation has abundant domestic copper ore reserves but because of many detrimental economic factors much of the copper used by t