natural mineral formations containing niobium in quantities that make economically feasible the extraction of niobium and its compounds.
Niobium ores contain a certain quantity of tantalum. A distinction is made between niobium ores, in which the Nb2O5: Ta2O5 ratio is greater than 20:1, and tantaloniobium ores, where the ratio is 3:1 to 20:1. The main niobium minerals that are components of niobium ores are columbite, (Fe,Mn)(Nb,Ta)2-O6, containing 50–76 percent Nb2O5, and pyrochlore, (Ca,Na)2(Nb,Ta,Ti)2O6(OH,F), in which the Nb2O5 content is 40–70 percent. Less important minerals include fergusonite, Y(Nb,Ta)O4 (38–58 percent Nb2O5); euxenite, Y(Nb,Ti,Ta)2O6 (21–34 percent); and loparite, (Na,Ce,Ca) (Ti,Nb,Ta)O3 ((7–20 percent). The minimum content of Nb2O5 at which native niobium ores may be worked profitably is 0.15–0.20 percent; the average content of Nb2O5 in most niobium ore deposits is 0.2–0.6 percent. Rich deposits contain 1–4 percent Nb2O5. The minimum content for processing of columbite gravel and deposits of the weathering mantle is 0.10–0.15 kg/m3.
All endogenous deposits of niobium ores are associated with alkaline or subalkaline rock. A number of main industrial types of niobium ore deposits are recognized. Pyrochlore carbonatites, which are actually calcitic endogenous rocks with insets of pyrochlore, apatite, magnetite, baddeleyite, and phlogopite, have an Nb2O5 content of 0.2–1.0 percent. Not less than 70 percent of the world reserves of niobium are associated with such deposits; the largest such deposits are in Araxá in Brazil and in Oka and St. Honoré in Canada. Loparitic lujauvrites are layers of loparite-enriched alkaline lujauvritic rock among stratified bodies of nepheline syenites composed of alternating members of rock of the lujauvrite, foyaite, and urtite types. They are a complex raw material from which niobium, tantalum, and titanium, as well as rare earths of the cerium group, are extracted. Columbite-pyrochlore granites and granosyenites form small bodies containing insets of columbite or pyrochlore with an Nb2O5:Ta2O5 ratio of the order of 10:1. The content of Nb2O5 in such bodies is usually 0.2 percent or more; the concentration is much greater in a weathering mantle. The largest deposit of this type is on the Plateau of Jos in Nigeria. Pyrochlore feldspathic quartziferous rocks, which develop metasomatically along rift zones in ancient metamorphic strata, are close to similar types of granites. This complex type of niobium ore containing rare-earth pyrochlore, zircon, and cryolite, has an Nb2O5 content of 0.2–0.5 percent. Pyrochloric albitites develop in zones of contact of bodies of nepheline syenites and have an Nb2O5 content that usually does not exceed 0.1–0.2 percent.
Exogenous deposits of niobium ores are sectional and particularly linear weathering mantles that develop on all the types of bedrock ores mentioned above, as well as alluvial, talus-alluvial, lacustrine, and fluvioglacial placers of columbite, pyrochlore, loparite, and less frequently, fergusonite and euxenite.
All the types of deposits mentioned above, with the exception of shallow seams of loparitic lujauvrites in stratified bodies of alkaline rock, are worked by opencut mining.
Gravitational methods are usually used to concentrate niobium ores. Flotation is used in cases of very fine dissemination of pyrochlore in carbonatites. Production of pyrochlore concentrates in 1972 was 7,600 tons in Brazil and 2,700 tons in Canada; production of columbite concentrates in Nigeria was 1,380 tons. In addition, Malaysia, Mozambique, and the Republic of Zaïre produced 220 tons of columbite concentrate. The consumption of Nb2O5 in capitalist countries in 1972 was estimated at 12,000 tons.
REFERENCESKuz’menko, M. V., and E. M. Es’kova. Tantal i niobii. Moscow, 1968.
Apel’tsin, F. R., and L. G. Fel’dman. Kolumbitonosynegranity. Moscow, 1958. (Geologiia mestorozhdenii redkikh elementov, fase. 2.)
Ginzburg, A. I., V. V. Arkhangel’skaia, and V. T. Shatskaia. “Polevosh-patovye metasomatity—novyi geneticheskii tip mestorozhdenii poleznykh iskopaemykh.” Razvedka i okhrana nedr, 1973, no. 1.
A. I. GINZBURG