LEAD AND ZINC Lead.—No quantitative estimate of the copper, lead and zinc resources of the world has been made and it is doubtful whether a reasonable approximation can be made. Looking backward through 5o years there have been periods when it was thought that the supply of these ores was superabundant and other periods when they have seemed to be scarce and opinion has swung from one extreme to another. Especially has this been true in the in stance of zinc. However, as to each of these metals, new dis coveries, both geographical and technological, may develop valu able resources out of what was previously unknown or worth less. The only conditions under which the world's resources of minerals can be reasonably forecast are when we may say that at least we have so much, as in the instances of coal and iron. Between these extremes it is always a matter of the equilibrium among production, consumption and price. So far as we can see ahead we shall have a sufficient supply of these metals, but we can not see clearly what price we shall have to pay for them, even through the next i o years.
The production of lead comes principally from the following districts, their percentages being given. South-eastern Missouri, 8.1; Utah, 4.7; Coeur d'Alene (Idaho), 5.1; Tri-State, cover ing the contiguous parts of Oklahoma, Kansas and Missouri, 2.7; Mexico, 14.1; Broken Hill, N.S.W., 10•4; Sullivan mine, Kim berley, B.C., io.6; Bawdwin mine, Burma, 4.7; Yugoslavia, 4.1. These account for about 65% of the world's production. Except in south-eastern Missouri, the mines produce a mixed ore which is milled so as to give an enriched galena product for the lead smelter and a blende product for the zinc smelter. Many of the great lead-producing districts of the past were exploited for lead alone, such as Eureka, Nev., and Leadville, Colo., and exhausted. Lead-producing districts have waxed and waned more generally and more rapidly than either copper or zinc. Because of this and the failure to make many important new discoveries since 1900, together with the greatly increased demand for lead, experts have taken a pessimistic view and predict a steadily rising price in order to develop poorer ores and remoter mines. About 1925 the new process of selective flotation enabled the profitable mining of large supplies of previously unworkable zinc-lead ores. Lead and zinc production became increasingly interlocked, and now the mines that produce straight lead or zinc ore are few. What will be said hereinafter under "zinc" will therefore apply equally to lead.
districts have lived and died, the most noteworthy of these having been Vieille Montagne (now of Belgium) and Leadville, Colo., but many new districts are being exploited. A maintenance of the output of the present large producing districts—Broken Hill, Tri State, Kimberley and Franklin—at the current rate for another 20 years, at least, may reasonably be forecast.
Estimates of zinc reserves collected from various sources total about 12,000,000 tons for the United States, or about a 20-year supply at the 1937 rate of production, but production from many deposits will be dependent on prices well above the levels current in recent years.
On the other hand new sources of production are being devel oped as the results of exploration of new territory, the extension of transportation and improvement of metallurgic processes, which not only make it possible to use profitably ores that formerly were considered refractory but also to give an increased yield from all ores. Among the important new districts are Flin Flon, Sudbury, Buchan (N.F.), Broken Hill (N. Rhod.), Roseberry (Tas.), Mount Isa, Cerro de Pasco (Peru), and Trepca (Yugoslavia). A. general upward trend of price was expected in 1925 as a conse quence of the increasing scarcity of zinc ore, but the advent of selective flotation changed that outlook almost immediately. Por tions of the world, as yet unexplored scientifically, may have great zinc ore possibilities as, northern Canada, Labrador, and New foundland; the Andes; Siberia, where there are some great known deposits; Africa, especially in the north and in the Congo region and in Rhodesia; the interior of Australia, and in New Guinea.
The production of ores up to quite recently has been from deposits whereof there have been surface indications. Much of the world's surface is covered by alluvial material which probably hides mineral deposits. We now have new developments in geo physical science and methods that are opening the way to the discovery of such hidden deposits. On the side of requirements, the need for all of these metals steadily increases. Immediately previous to the World War the annual per caput consumption of the United States was about 8 lb. of copper, 9 of lead and 6.5 of zinc. In the principal countries of Europe the average was a little less, especially of copper. In 1929 the American per caput con sumption was about i8 lb. of copper, 12 of lead and io of zinc. European consumption was, however, still below the pre-war rate. In 1937 the United States consumption was 111b. copper, 81b. lead, and 8.51b. zinc, while Europe had risen to 141b. copper, 161b. lead, and 'db. zinc, as a result of increased rearmament demand. The intimate connection between these metals and the electrical and other important basic industries promises continued increase in demand, while prospects for extensive substitution are limited to the use of aluminium instead of copper for electrical transmission lines. (G. A. Ro.)