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any natural mineral containing uranium or uranium compounds in concentrations that make commercial use technically feasible and economically advantageous.
Approximately 100 uranium minerals are known, of which 12 have practical importance. The most important for industry are uranium oxides (uraninite, pitchblende, “uranium black”), silicates (coffinite), and titanates (davidite, brannerite); the uranite group, consisting of aqueous phosphates and uranyl arsenates, is also important.
Uranium ores are divided into three groups on the basis of the conditions surrounding their formation. The endogenic ores—the first group—were precipitated at high temperatures and pressures from pegmatite melts and aqueous (presumably postmag-matic) solutions; ores of this type are characteristic of folded regions and activated cratons. The second group comprises exogenous ores, formed near and on the surface of the earth during sediment accumulation (syngenetic ores) or as a result of the circulation of groundwater (epigenetic ores); they are associated primarily with young cratons. Metamorphic ores make up the third group. Formed through the redistribution of initially dispersed uranium during the metamorphism of sedimentary layers, these ores are typical of ancient cratons.
Uranium ores are also classified on the basis of physical characteristics and commercial suitability. According to the nature of uranium mineralization, distinctions are made between primary uranium ores, which contain at least 75 percent U4+; oxidized uranium ores, containing mainly U6+; and mixed ores, in which U4+ and U6+ are present in approximately equal proportions. The degree of oxidation of uranium minerals is reflected in the technology for processing the ores and in the ores’ behavior during hydrometallurgical conversion. Depending on the degree of contrast, which is determined by the amount of evenness in uranium content in a piece of rock, ores are classified as highly contrasted, contrasted, weakly contrasted, or noncontrasted. Contrast determines whether radiometric concentration is warranted. Depending on the dimensions of the aggregates and grains of uranium minerals, distinctions are made between large-grained (more than 25 mm in diameter), medium-grained (3–25 mm), small-grained (0.1–3.0 mm), fine-grained (0.015–0.100 mm), and dispersed (less than 0.015 mm) ores. The dimensions of the aggregates and grains determine whether mechanical concentration is possible.
According to the content of useful impurities, the ores are classified as, for example, uranium ores proper, uranium-molybdenum ores, uranium-vanadium ores, or uranium-nickel-cobalt-bismuth-silver ores.
The chemical composition of the nonmetalliferous components of the ores determines the classification of uranium ores as silicate (primarily silicate minerals), carbonate (more than 10–15 percent carbonate minerals), iron-oxide (iron-uranium ores), sulfide (more than 8–10 percent sulfide minerals), or caustobiolith (primarily organic matter).
The chemical composition of the ores is frequently decisive in choosing the method of processing. For example, uranium is leached from silicate ores by acids and from carbonate ores by soda solutions. Iron-oxide ores are subjected to smelting in blast furnaces, during which uranium is concentrated in the slag. Caustobiolith ores are sometimes concentrated by roasting.
The five ore grades based on uranium content are very rich (more than 1 percent uranium), rich (0.5–1.0 percent), average (0.25–0.50 percent), run-of-mine (0.10–0.25 percent), and lean (less than 0.1 percent). Uranium is extracted as a by-product from ores containing 0.010–0.015 percent uranium, for example, the gold-bearing conglomerates of Witwatersrand, Republic of South Africa, and even 0.006–0.008 percent uranium, as in the phosphorites in Florida, in the United States.
In 1977 world production of uranium concentrates (excluding the socialist countries) was 30,620 tons. The main deposits of uranium ores in the capitalist countries are in the United States (Colorado Plateau), Canada (Ontario and Saskatchewan), France (Massif Central), and South Africa (Witwatersrand). There are also large deposits in Australia (Northern Territory) and Gabon.
REFERENCESSurazhskii, D. Ia. Metody poiskov i razvedki mestorozhdenii urana. Moscow, 1960.
Pribytkov, P. V. “Osnovnye printsipy klassifikatsii promyshlennykh uranovykh rud.” Atomnaia energiia, 1960, vol. 9, issue 3.
Rudnye mestorozhdeniia SSSR, vol. 2. Moscow, 1974.
D. IA. SURAZHSKII