700 



UNITED STATES MINERAL RESOURCES 



rupted only by periods of political and economic 

 stress, as during the First World War when Belgian, 

 French, and Dutch smelter output was sharply cur- 

 tailed, and during the 1918-22 economic depression 

 which followed that war. The economic depression 

 of the early 1930's is clearly reflected in the g \phs 

 for both world and U.S. production, and the effect 

 of the outbreak of the Second World War on west- 

 ern European smelter output is reflected in world 

 production decrease for 1941; U.S. production in- 

 creased that year. 



The most striking feature of the U.S. graph is 

 that while consumption has grown consistently dur- 

 ing and since the 1940's, mine production has re- 

 mained nearly static, or has actually declined, so 

 that during the period 1950-70 about half of U.S. 

 needs have been met by imported materials, mainly 

 ores and concentrates processed by U.S. smelters 

 located near seaports. Increasing dependence on for- 

 eign zinc in recent decades has been due not so much 

 to depletion of domestic deposits as to the lower 

 cost of imported materials in relation to production 

 costs at domestic mines. The U.S. imbalance will be 

 aggravated further, at least through the mid-1970's, 

 because of the closing of seven domestic zinc smelt- 

 ers between 1969 and 1972, brought about by obso- 

 lescence coupled with antipollution regulations. 



Most significant is the fact that between 1950 and 

 1970 mankind consumed half of all the zinc pro- 

 duced in the world up to 1970, and between 1960 

 and 1980 will probably consume about as much zinc 

 as was produced in all of history before 1960 — that 

 is, about 106 million short tons. 



The year-to-year exploitation of zinc deposits will 

 continue to be sensitive to economic conditions, but 

 the probable trend will be one of growth, reflecting 

 world population growth, increasing industrializa- 

 tion in developing nations, and the desire for a 

 higher standard of living everywhere. However, the 

 phenomenal increase in the production and consump- 

 tion of zinc in the 20th century cannot continue 

 indefinitely, and eventually production must decline 

 as primary resources approach exhaustion. We be- 

 lieve that this point of irreversible decline is still 

 several decades into the future, and is not likely to 

 occur until the next century. Meanwhile, the indus- 

 try, to prolong its survival, can be expected to seek 

 improvements and innovations in mining and metal- 

 lurgical techniques which will permit the exploita- 

 tion of lower grade and unconventional types of 

 deposits and the recovery of metal on a scale not 

 previously possible, at the same time eliminating 

 damage to the environment caused by current min- 

 ing and smelting operations. 



GEOLOGIC ENVIRONMENT 



GEOCHEMISTRY 



Zinc is a chemical element of atomic number 30 

 and atomic weight 65.38 ; it consists of the following 

 isotopes: Zn"*', 48.89 percent; Zn"% 27.81 percent; 

 Zn'=", 4.11 percent; Zn'=% 18.56 percent; and Zn"°, 

 0.62 percent (Rankama, 1963, p. 579, 583). In four- 

 fold coordination, zinc (Zn= + ) has an ionic radius 

 of 0.71 A; in six-fold coordination, an ionic radius 

 of 0.74 A (Green, 1959, table 2). These radii are 

 close to those of Mg=+ (0.66 A), Cu=+ (0.72 A), and 

 Fe=+ (0.74 A) (Green, 1959, table 2). Chemically, 

 zinc is most similar to cadmium and mercury, the 

 other two elements of Group lib of the periodic 

 system. 



The range of estimates of the average crustal 

 abundance of zinc is from 65 to 94 ppm (parts per 

 million). It thus ranks ahead of copper (45-63 ppm) 

 and lead (12-16 ppm), with both of which it is 

 commonly associated in ore deposits. Mason (1958, 

 p. 41) listed zinc as the 23d most abundant element 

 in the earth's crust. Its concentration in igneous 

 rocks varies from 130 ppm in basalts and syenites 

 through values of 72 ppm in rocks of intermediate 

 composition and 39-60 ppm in acidic rocks. The 

 sedimentary rocks, such as sandstone, shale, and the 

 carbonates, average 16 ppm, 95 ppm, and 20 ppm, 

 respectively. Some carbonaceous shales are reported 

 to contain as much as several thousand parts per 

 million, whereas the Kupferschiefer of Europe may 

 contain as much as 60,000 ppm, and although the 

 average is something less, will contain several per- 

 cent of combined copper-lead-zinc over large areas. 

 Deep-sea clays reportedly average 165 ppm, and 

 muds from the Atlantis II Deep in the Red Sea 

 average 34,000 ppm. In western Canada, some dolo- 

 mites may contain several thousand parts per mil- 

 lion and in South Australia 1-2 percent zinc is 

 reported as at least in part in solid solution in dolo- 

 mite. (See Bischoff and Manheim, 1969; Dunham, 

 1964; Krauskopf, 1967; Muller and Donovan, 1971; 

 Parker, 1967 ; Lee and Yao, 1970 ; Weber, 1964.) 



Broad geochemical classifications of the elements 

 generally group them as to (1) lithophile, sidero- 

 phile, or chalcophile, and (2) oxyphile or sulfophile. 

 Most lithophile elements rarely produce sulfide or 

 related minerals in nature; they have a marked 

 aflSnity for oxygen, and are enriched in the silicate 

 crust or lithosphere. Chalcophile elements, con- 

 versely, have a strong attraction for sulfur, and 

 siderophile elements are so named because they are 

 enriched in the nickel-iron phase (siderosphere) as 

 known from meteorites. The classification as oxy- 



