164 



UNITED STATES MINERAL RESOURCES 



It is possible to speculate that another 320 million tons of 

 eopi>er might be found in areas not yet prospected and 

 in which important deposits are unknown. The most promis- 

 ing areas lie in the Basin and Range province of the United 

 States, outside the known porphyry copper province; in the 

 U.S.S.R. Far East where porphyry copper provinces may be 

 found in Mesozoic fold belts and the younger island arc sys- 

 tem; and in the Brazilian shield where major sedimentary 

 copper deposits might be found. 



The aforementioned identified, hypothetical, and specula- 

 tive categories refer to known or postulated ore deposits, 

 minable under present economic and technological conditions. 

 In addition to these are large conditional resources in 

 porphyry copper, sedimentary copper, and igrneous copper- 

 nickel deposits and in manganese nodules on the sea floor. 

 At least 381 million tons of copper in such subeconomic de- 

 posits can be identified or hypothesized. This copper may be- 

 come available at some future period of high metal prices 

 and (or) improved technology. 



A comparison of current U.S. and world production and 

 the copper content of various copper deposits shows that 

 the United States produces enough copper to mine out an 

 average-sized porphyry copper deposit each year. Maintain- 

 ing a balance between deposits discovered and deposits 

 mined out means that a great investment in geological, geo- 

 chemical, and geophysical studies must be made and main- 

 tained in spite of short-term fluctuations in the price of 

 copper. 



PROPERTIES, USES, AND RESOURCES 



Copper, one of the most useful and versatile 

 metals, has been used by man perhaps longer than 

 any other metal except gold. Its unique physical and 

 mechanical properties are utilized both in its metal- 

 lic state and in alloy with many other metals. Cop- 

 per, chemical symbol Cu, has a hardness (Mohs' 

 scale) of 2.5-3, a melting point of 1,083°C, a boil- 

 ing point of 2,595°C, a density (annealed at 20°C) 

 of 8.89, and an electrical resistivity at 20°C of 1.71. 

 Its electrical conductivity in cross section and by 

 weight is surpassed only by silver and by aluminum, 

 respectively. 



High electrical and thermal conductivities, good 

 resistance to corrosion, good ductility and malle- 

 ability, high strength, lack of magnetism, and a 

 pleasing red color are properties and characteristics 

 of copper that find innumerable industrial applica- 

 tions. Copper and many of its alloys can be joined 

 by welding, brazing, and soldering. It can be fin- 

 ished by plating and lacquering. 



The four traditional copper-base alloys, brass, 

 bronze, nickel-silver, and cupronickel, contain no 

 less than 40 percent copper, with the amount of 

 copper not less than that of any other constituent. 

 Copper also is used in many other alloys where it 

 is not the major component. 



About half (53 percent) of the 1.5 million tons 

 of copper used domestically in 1970 was for elec- 



trical applications, followed by 16 percent in con- 

 struction, 12 percent in industrial machinery, 8 per- 

 cent in transportation, 6 percent in ordnance, and 

 5 percent in other uses. 



Use of copper in all applications for which it is 

 suited would exceed its available supply, but alumi- 

 num has substituted for copper in many applica- 

 tions. In the last two decades U.S. consumption of 

 aluminum has more than tripled, while the use of 

 copper increased only 15 percent. Although copper 

 is virtually indispensable for some applications, 

 aluminum serves satisfactorily as an alternate metal 

 in many others, and often at lower cost. The rela- 

 tive capabilities of the two metals in their electrical 

 conductor applications depend on their physical and 

 mechanical properties. For example, an aluminum 

 conductor weighs only 30 percent as much as a 

 copper conductor of identical size, but an aluminum 

 conductor has 1.64 times the electrical resistance of 

 a copper conductor of equal size. Thus, for equal 

 current-carrying capacity, an aluminum conductor 

 weighs half as much as a copper conductor, but has 

 a cross-sectional area 26 percent greater. 



Aluminum and stainless steel are used in place of 

 copper for some applications in the building indus- 

 try. Steel increasingly replaces brass in shell cases. 

 The use of copper cladding proportionately requires 

 less copper than would solid copper; copper now 

 substitutes for silver in coins which have a copper 

 core and a cupronickel cladding material. Printed 

 electrical circuits and plastics have replaced copper 

 in many applications. These shifts in the overall 

 use pattern make more copper available for pre- 

 ferred uses. In spite of substitution, the continued 

 use of a substantial part of our present copper re- 

 quirement is needed to maintain or present living 

 standard. 



The supply to meet domestic demand is derived 

 from U.S. mine production, secondary production 

 (recovery of old scrap), imports, and withdrawals 

 from industrial and Government stockpiles. The 

 trends in supply and demand for copper during the 

 period 1950-70 are illustrated in figure 20 and 

 table 36. Other demand forecasts to the year 2000 

 are discussed by Lowell (1970) and by Ageton and 

 Greenspoon (1970). 



Copper is traded in a number of commercial 

 classes — ore, concentrate, matte, blister, refined, and 

 secondary — each with varying percentages of cop- 

 per content. Because of the complexity in deter- 

 mining the total amount of copper used from all 

 classes and the many demands of trade such as 

 imports, exports, and stockpiles, the total demand 



