180 



UNITED STATES MINERAL RESOURCES 



erals similar to the zeolite facies described by 

 Coombs, Ellis, Fyfe, and Taylor (1959). The source 

 of mineralizing solutions for the copper sulfide de- 

 posits in the Nonesuch Shale and the native copper 

 deposits in the Portage Lake Volcanics may be 

 essentially the same — namely, the 15,000-30,000 

 feet of flood basalts at depth in the Lake Superior 

 Basin (Ensign and others, 1968, p. 486). The 

 copper-bearing solutions, according to White (1968, 

 p. 322), may represent water driven from the voids 

 and interstices of flow tops as the lava flows were 

 crushed and metamorphosed in the axial region of 

 the Lake Superior syncline, downdip from the pres- 

 ent deposits. 



Other copper occurrences that resemble the Ke- 

 weenaw type are the chalcocite-bearing Coppermine 

 deposits in gently dipping basalt flows of Precam- 

 brian Y age in the Northwest Territories, Canada, 

 and the native copper-cuprite-azurite-malachite 

 ores in chloritized and epidotized mafic flows in the 

 Catoctin Formation (Precambrian Z) of Maryland 

 and Virginia. Chilean copper deposits in terrestrial 

 volcanic rocks such as Buena Esperanza (Ruiz and 

 others, 1971) may be similar in origin to the Kewee- 

 naw type, although they lack native copper. Bornite, 

 chalcocite, and chalcopyrite are found in amygda- 

 loidal upper parts of andesite flows in these deposits. 



MISCELLANEOUS TYPES 



Some copper deposits of local and (or) historic 

 importance differ significantly in form and rock 

 association from those of the five major groups just 

 described. Among these are small and very high 

 grade chalcocite deposits such as Kennecott, Alaska, 

 and Mountain City, Nev. (See fig. 22 for compari- 

 son with other types.) Nearby volcanic rocks have 

 been called upon as a source of copper in these 

 deposits (Coats and Stephens, 1968; E. M. Mac- 

 Kevett, written commun., 1972). The massive chal- 

 copyrite lenses and veins of Matahambre, Cuba, 

 appear to be unrelated to either volcanic or intru- 

 sive rocks (R. A. Bradley, oral commun., 1972). The 

 sulfide lenses in shears crosscutting anorthosite 

 bodies at Chibougamau, Quebec, do not lend them- 

 selves to inclusion with any of the previously de- 

 scribed types. 



Replacement ore bodies in carbonate rocks far 

 from an igneous source, such as at Bornite-Ruby 

 Creek, Alaska (Runnels, 1969), may be an im- 

 portant resource of copper. Numerous lodes of this 

 type in a 450-mile belt along the south slope of the 

 Brooks Range, Alaska, are believed to contain more 

 than 10 million tons of copper metal. Small copper 

 production (12,000 tons in 1970) from Missouri is 



a byproduct of the lead-zinc replacement bodies in 

 carbonate rocks without igneous affiliation (Allen 

 Heyl, oral commun., 1972). 



RESOURCES 

 IDENTIFIED AND HYPOTHETICAL RESOURCES 



About 70 percent of the world's identified copper 

 resources fall into four distinct geologic-geographic 

 groups. These are, in decreasing importance, por- 

 phyry copper deposits of Chile and Peru, porphyry 

 copper deposits of the Southwestern United States, 

 sedimentary copper deposits of Zaire and Zambia, 

 and porphyry copper and sedimentary copper de- 

 posits of the U.S.S.R. Other important groups are 

 the porphyry copper deposits in Oceania, in Mexico, 

 and in western Canada and the porphyry copper 

 and sedimentary copper deposits in southeastern and 

 central Europe, respectively. Volcanogenic deposits 

 and nickel-copper deposits in mafic intrusions, im- 

 portant as they may be to local economies, do not 

 contribute significantly to the worldwide picture. 



Identified copper resources, given in table 39, are 



Table 39. — Identified and hypothetical copper resources, in 

 millions of short tons 



^Identified resources: Specific, identified mineral deposits that may 

 or may not be evaluated as to extent and grade and whose contained 

 minerals may or may not be profitably recoverable with existing tech- 

 nology and economic conditions. Based on all categories of reserve figures 

 plus estimates where no figures are available. Amounts are tentative and 

 accuracy will be refined in subsequent publications. 



- Hypothetical resources : Undiscovered mineral deposits, whether of 

 recoverable or subeconomic grade, that are geologically predictable as 

 existing in known districts. Based generally on identified resource figures 

 times a factor assigned according to geologic favorability of the region, 

 extent of geologic mapping, and exploration. 



those for which a size estimate is available. All 

 categories of reserve figures as well as estimates 

 for deposits where no reserve figures are published 

 have been combined to make up this identified re- 

 source. These figures should be regarded as tenta- 

 tive, and considerable refinement of their accuracy 

 should be expected in subsequent publications. They 

 are derived from unpublished resource compilations 

 made by A. R. Kinkel and others in the early 1960's, 

 with additions and subtractions based on new dis- 



