a natural mineral formation containing chromium in such compounds and concentrations as to make its commercial exploitation technically feasible and economically expedient.
The only chromium-containing minerals that provide an industrial source of chromium are the chrome spinellids. In addition to chrome spinellids, the primary minerals of chrome ores are the silicates, including serpentine, chlorite, and sometimes olivine, pyroxene, plagioclase, uvarovite, chrome actinolite, talc, and brucite, and the carbonates and sulfides.
A distinction is made between solid and impregnated chrome ores. The latter are further subdivided into densely impregnated (50–80 percent chrome spinellids), heavily impregnated (30–50 percent), and lightly impregnated (10–30 percent). Different combinations of massive structures with banded, mottled, nodular, and other types of structures are observed. The quantity of the leading components in chrome ores varies as follows: 10.5–62.0 percent by weight Cr203, 4.0–34.0 percent Al2O3, 1.0–18.0 percent Fe2O3, 7.0–24.0 percent FeO, 10.5–33.0 percent MgO, and 0.4–27.0 percent SiO2. Certain chrome ores contain 0.1–0.2 g/ton of the platinum group elements and up to 0.2 g/ton of gold. The harmful impurities S, P, and Ca constitute more than 1.0 percent.
The form of the ore bodies differs. In stratiform massifs of platform regions, the ore bodies are in the form of layers that extend for dozens of kilometers but are quite thin, ranging from a few dozen centimeters to a few meters. In the massifs of folded regions, they occur in the form of extremely elongated lenses stretching from hundreds of meters to 1.5–2.0 km and ranging from a few meters to 150–180 m in thickness at the bulges; veinlike bodies extending from a few dozen meters to 1,000–1,500 m in length and ranging in thickness from 2 to 15–20 m; and stocks and irregular formations of various sizes. Deposits of chrome ores are classified as true magmatic formations formed during the crystallization of basaltic and ultrabasic magmas.
Three chrome ore-bearing formations are identified: the peridotite-orthopyroxenenorite formation on the platforms and the peridotite and gabbronorite-peridotite formations in geosynclinal regions. Chrome ores are also known to occur in deluvial, eluvial, and coastal alluvial deposits. A distinction is made between metallurgical, refractory, and chemical ores, depending on industrial use. Chrome ores are mined by open-cut and underground methods in approximately the same proportions. The ungraded chrome ores are concentrated by the gravitation-flotation method; the extraction rate is 80–95 percent.
The chief deposits of chrome ores in the USSR are in the Urals at the Donskoe and Sarany deposits. The principal deposits abroad are in the Republic of South Africa (the Bushveld complex), Zimbabwe (the Great Dike and Selukwe), Turkey (Guleman and elsewhere), the Philippines (primarily on the island of Luzon, at Masinloc and elsewhere), India (Sukinda and elsewhere), Finland (Kemi), and Madagascar (Andriamena).
At the beginning of 1977, the chromeore reserves of the capitalist and developing countries amounted to 1.679 billion tons, of which the Republic of South Africa accounted for 1.050 billion, Zimbabwe for 550 million, Finland for 30 million, Turkey for 10 million, India for 7 million, and the Philippines for 7 million. In 1975 the following amounts of chrome ores were extracted (in tons): 2.4 million in the Republic of South Africa, 500,000 in Zimbabwe, 868,000 in Turkey, 422,000 in the Philippines, and 401,000 in India.
REFERENCESTrebovantia promyshlennosti k kachestvu mineral’nogo syr’ia, 2nd ed., fasc. 15: S. S. Gorlanov, Khromit. Moscow, 1963.
Rudnye mestorozhdeniia SSSR, vol. 1. Moscow, 1974.
N. V. PAVLOV