RARER ELEMENTS Cobalt, molybdenum, tantalum and columbium, uranium and radium, and zirconium are included here as representatives of the group of rarer elements, the commercial importance of which is less than that of the metals considered in the previous sections.
Production in 1938 was estimated at 4,200 metric tons, of which Belgian Congo contributed 36%, Northern Rhode sia 35%, French Morocco 18%, and Canada and Burma each 5%; in addition to these there are minor unknown outputs in Australia, Finland, Germany, Greece, Japan, and China. Other deposits which have not yet been proven of commercial importance are known in Chile, Uganda, Norway, Sweden, New Caledonia, the Caucasus, and Pennsylvania (U.S.A.). The chief ores are smaltite
and cobaltite (CoAsS), but the metal is also found in a number of non-commercial minerals. In nature its occurrence is usually closely associated with nickel, but curiously enough the world's largest nickel deposit, in the Sudbury district of Ontario, carries no cobalt.
The deposits of Belgian Congo and Northern Rhodesia, which now supply the bulk of the output, are of comparatively recent development, and the Cobalt district of Ontario, which furnished almost the entire supply in the early 1900's, is now the smallest of the leading producers. The reserves seem to be sufficient for any demand likely to be made on them for some years to come, but no specific data are available.
The extent to which our knowledge of re serves may be altered in a comparatively few years, and the diffi culty in predicting the prospective life of the reserves, is well il lustrated by the case of molybdenum. In 1923 it was reported that the Climax mine, near Leadville, Colo., was capable of pro ducing i,000 tons of ore daily for a period of 3o years; this was equivalent to about 72,000,000lb. of contained molybdenum, and at the time was considered to be a heavy reserve, in comparison with the demand. Since then molybdenum consumption has in creased so rapidly that the known reserves of 1923 would have been exhausted by 1936, but, at that time, instead of exhaustion, reserves were reported at 720,000,000lb. of contained molybde
num, or ten times the 1923 figure; although in the meantime pro duction had been stepped up to 12,000 tons of ore daily, instead of the i,000 tons envisaged in the 1923 report, the prospective life of the reserves had been little changed. Incidentally, it is interest ing to note that the known reserves of 1923 would have been com pletely wiped out by the production of the three years 1936-1938.
Although molybdenum minerals have been found to be widely scattered over the United States, commercial production outside of Colorado is limited to Alaska, Arizona, Idaho, Nevada, Utah, and Washington, with 85% of the total from the Climax mine. The United States output has averaged about 90% of the world total, other producing countries, in order of importance, being Mexico, Norway, French Morocco, and Peru. In the decade from 1929 to 1938 world production increased eightfold, from 4,313,000lb. to 36,016,000lb. of metal.
Tantalum associated with co lumbium or niobium is found widely distributed in many rare earth minerals, but the chief sources are the minerals columbite and tantalite, two minerals which are identical except for the rela tive amounts of tantalum and columbium present. The general symbol representing their composition is
and in various samples the ratio between the iron and manganese and the tantalum and columbium differs. In general, tantalite is high in tantalum and columbite in columbium. Some ores from Aus tralia run as high as 5o% to 7o%
In the Black Hills of South Dakota and in Connecticut, U.S.A., ores have been found ranging from io% to 4o%
Tantalum ores have also been reported from Maine, Massachusetts, New York, Pennsyl vania, Virginia, North Carolina, Colorado and California in the United States, and from Norway, Sweden, Finland, Russia, Ba varia, Italy, and the Malay States. The combined production of tantalite and columbite in 1937 was about ',coo short tons, of which Nigeria supplied 8o%, Belgian Congo 13%, Uganda 3%, Australia 2%, United States o.8%, and South West Africa, South Africa, Southern Rhodesia, and India the remainder.