Ore Deposit


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ore deposit

[′ȯr di‚päz·ət]
(geology)
Rocks containing minerals of economic value in such amount that they can be profitably exploited.

Ore Deposit

 

an accumulation of an ore body or ore bodies on or below the surface of the earth that, because of size, quality, and mode of occurrence, is suitable for industrial exploitation. Ore deposits consist of one ore body or several ore bodies that can be worked together. They are formed by all the geological processes that contribute to the formation of the earth’s crust.

Various stages and steps of ore formation are distinguished in the formation of ore bodies. A stage of ore formation is a period of time in which ore-forming minerals of a certain composition accumulate under more or less stable geological and physicochemical conditions; the period is separated from other stages by an interval of mineralization. The interval between stages of ore formation usually corresponds to a period of tectonic inactivity, which terminates at the beginning of a new stage in tectonic deformation and the opening of the ore cavity; the opening of the ore cavity is often accompanied by a grinding of the mineral material of the previous stage.

On the basis of the number of stages involved in the formation of an ore deposit, a distinction is made between simple, one-stage and complex, multistage deposits. The total number of stages is usually 4–6 and rarely exceeds ten. The mineral associations of consecutive stages of ore formation are called mineral generations. The mineral composition of these generations may be different, the same, or partially repeated.

A long period of mineral accumulation combining a number of consecutive stages and related to a single genetic process is called a step of ore formation. The ores of one deposit usually belong to a single step of mineral accumulation, less frequently to two or more. For example, in the upper segments of ore shoots there may be mineral masses of the primary hydrothermal step and a step caused by secondary oxidation of the ore near the earth’s surface. An ore deposit may also form as a result of several steps of processes that are identical but belong to different periods of geological history.

Ore deposits are divided into deposits of ferrous, light, non-ferrous, noble, rare, and radioactive metals and deposits of trace elements.

Ore deposits of ferrous metals include deposits of iron, manganese, chromium, titanium, and vanadium. The reserves of the most plentiful of these ore deposits total billions of tons, with the metal content amounting to several tenths of the total. Deposits of iron ores are the most abundant and the most varied in their modes of occurrence. The most significant of these deposits are metamorphogenic hematite and magnetite deposits of Precambrian ferruginous quartzites. Major deposits are found in the Krivoi Rog Iron Ore Basin and the Kursk Magnetic Anomaly in the USSR, the Lake Superior Iron Ore Region in the USA, and the Labrador Iron Ore Belt in Canada. The Kerch’ Iron Ore Basin in the USSR, with its deposits of sedimentary brown hematite, siderite, and iron chlorite, is of great industrial importance. Deposits of manganese ores are classified as sedimentary oxide and carbonate ores; the latter are found in the Nikopol’ Deposit in the Ukraine and the Chiatura Deposit in Georgia. Significant metamorphosed deposits are found in India, Africa, and Brazil.

Industrial deposits of chromium, all of which are magmatic formations, are found in the Urals, South Africa, India, and Turkey. Industrial deposits of titanium ores, which are genetically related to basic and alkaline rock, are found in the USSR, the USA, Canada, the Arab Republic of Egypt, and the Republic of South Africa. Vanadium ores are mined from deposits of magmatic vanadium-bearing titanomagnetite, deposits of sedimentary vanadium, and vanadium-bearing deposits.

Ore deposits of light metals are represented by aluminum deposits. The major source of aluminum ores is bauxites, deposits of which are ocean deposits and formations of the weathering mantle. Paleozoic deposits of bauxites are found in the Urals and on the East European Platform. Mesozoic deposits are found in the Mediterranean and Australian bauxite provinces. Cenozoic bauxite deposits are concentrated in the tropical belt of Africa, India, and Guiana. Kyanite, alunite, nepheline, and clay deposits are nonbauxite aluminum ores and require a more complex and expensive technology for obtaining aluminum.

Ore deposits of nonferrous metals include deposits of copper, lead, zinc, cobalt, nickel, and antimony. The metal reserves in the largest deposits range from tens of millions to hundreds of millions of tons; metal content in the ore is usually less than 10 percent. A significant amount of copper ore is obtained from stratiform deposits of copper-bearing sandstones and shales, which are found in Dzhezkazgan in Kazakhstan, Udokan in Siberia, South Africa, and Poland. Another major source is the hydrothermal stockworks of copper-porphyritic ores, found in Kounrad in Kazakhstan, Almalyk in Uzbekistan, Kadzharan in Armenia, and a series of deposits in the Cordilleras and Andes in Canada, the USA, Chile, and Bolivia. Copper is obtained from volcanogenic pyrites in the Urals, Spain, Turkey, and the Federal Republic of Germany. It is also obtained from hydrothermal veins, such as those in the Zangezur Range in the Armenian SSR and near Butte in the USA. A significant amount of copper is extracted when magmatic sulfide coppernickel deposits are mined in the Noril’sk Ore Region and Pechenga in the USSR and at Sudbury in Canada.

Lead and zinc usually occur together in nature in complex ores. Major ore sources include stratiform sheetlike deposits in carbonate rocks, such as the Zhairem and Mirgalimsai deposits in Kazakhstan, the Mississippi Valley Lead and Zinc Deposits in the USA, and deposits in Upper Silesia in Poland. In addition, lead and zinc ores are obtained from volcanogenic pyrites in the Rudnyi Altai in the USSR and near Mount Isa in Australia and from hydrothermal metasomatic deposits in carbonate rocks near Dal’negorsk in the Soviet Far East, in the Gorevka basin in the Enisei Ridge, the USA, Mexico, and Yugoslavia. They are also obtained from hydrothermal veins near Sadon in the Caucasus and in the USA, Australia, Czechoslovakia, and the German Democratic Republic. Most cobalt and nickel is obtained from magmatic copper-nickel deposits, such as those near Noril’sk and Pechenga in the USSR and Sudbury and Thompson in Canada, and from deposits related to the crust of the weathering of silicate composition, which are found in the Southern Urals, Cuba, Brazil, and New Caledonia. All deposits of antimony ores are related either to hydrothermal sheets, as in the case of the deposits near Kadamdzhai in Soviet Middle Asia and deposits in the People’s Republic of China, or to hydrothermal veins, as in the case of the deposits near Saralakh in Yakutia.

Deposits of tin, tungsten, molybdenum, mercury, beryllium, tantalum, and niobium are characteristic of ore deposits of rare metals. The greatest reserves of these ores reach hundreds of thousands of tons, with the metal content in the ore usually not greater than 1 percent. A significant amount of tin ore is obtained in the treatment of hydrothermal sulfide-cassiterite and quartz-cassiterite deposits in Kolyma, Primor’e, and Transbaikalia, Bolivia, the German Democratic Republic, and Great Britain. In addition, tin is obtained from placer deposits, the best known of which are on the Pacific islands. Tungsten ores are concentrated in hydrothermal vein and stockwork wolframites in Transbaikalia, Kazakhstan, the People’s Republic of China, Burma, and Bolivia, as well as in skarn scheelite deposits in Tyrnyauz in the Caucasus, Middle Asia, the USA, Burma, and the People’s Democratic Republic of Korea.

Molybdenum ore is obtained by working stockwork and vein hydrothermal deposits in the Krasnoiarsk Krai, Transbaikalia, and Kazakhstan in the USSR and in Climax in the USA. It is also obtained from skarn deposits of the type found in Tyrnyauz in the Caucasus. All mercury ore is obtained from hydrothermal deposits, the most important of which are sheet deposits in the Donets Coal Basin, Middle Asia, Spain, Italy, Yugoslavia, and the People’s Republic of China. Of the various sources of beryllium ores, the most significant are deposits of pegmatite, hydrothermal quartz, fluorite with beryl, greisen and skarn with helvite and phenakite, and volcanogenic deposits of fluorite-bertrandite and gelbertrandite composition. Tantalum and niobium ores are obtained from magmatic deposits among nepheline syenites, carbonatites, albitites, and pegmatities.

Noble metals include deposits of gold, platinum group metals, and silver. The largest of these deposits are only very rarely in the tens of thousands of tons and usually total only tens and hundreds of tons; the content of gold, for example, rarely exceeds 10 g per ton (0.001 percent). The most common type of gold ores is the hydrothermal veins and stockworks of quartz and other minerals that bear gold, such as the deposits in the northeastern USSR, Western and Eastern Siberia, the Urals, Kazakhstan, Middle Asia, and the Caucasus. Another important source of gold are volcanogenic hydrothermal complex gold-silver ores, such as those in the Pacific Geosynclinal Belt in the USSR, Canada, the USA, Chile, Peru, and Bolivia. A unique deposit of gold is found in the Precambrian conglomerates of the Witwatersrand, which supplies more than half of the gold produced worldwide and is considered by most geologists to be an ancient metamorphosed placer deposit. Platinum group metals are obtained mainly by treating complex platinum-metal-bearing magmatic sulfide copper-nickel ores of the type found in the Noril’sk Ore Region in the USSR and at Sudbury in Canada.

Ore deposits of radioactive metals include deposits of uranium (radium) and thorium. The reserves of uranium, the major radioactive metal, contained in individual deposits total thousands and tens of thousands of tons (rarely more), with the usual content of metal in the ore amounting to tenths of 1 percent. Hydrothermal and sedimentary deposits are very important sources of uranium ores. Thorium deposits are closely related to granitoid and alkaline rocks; most of the metal is found in accessory minerals, such as monazite, zircon, xenotime, and orthite. Some thorium is accumulated in pegmatites and some is concentrated with ores of tin, lead, zinc, silver, cobalt, nickel, and uranium.

Ore deposits of the trace elements are found in sedimentogenic, magmatogenic, and metamorphogenic deposits and are obtained as a secondary product in the treatment of these ores.

Ore deposits of rare-earth elements of the cerium and yttrium groups are related to magmatic, pegmatite, carbonatite, albitite, hydrothermal, and placer deposits of ferrous, rare, and radioactive metals and are obtained mainly as by-products in the treatment of the deposits.

REFERENCES

Magak’ian, I. G. Rudnye mestorozhdeniia, 2nd ed. Yerevan, 1961.
Park, C. F., and R. A. MacDiarmid. Rudnye mestorozhdeniia. Moscow, 1966. (Translated from English.)
Smirnov, V. I. Geologiia poleznykh iskopaemykh, 2nd ed. Moscow, 1969.
Kotliar, V. N. Osnovy teorii rudoobrazovaniia. Moscow, 1970.

V. I. SMIRNOV

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