karbonatiti

Karbonatiti, known in English as carbonatites, are rare igneous rocks in which carbonate minerals constitute the majority of the rock. By definition, carbonate minerals exceed 50% of the mineral composition, and the silicate portion, if present, is generally low. They are commonly silica-undersaturated and are often closely linked with alkaline magmatism.

The silicate portion, when present, is usually sparse and includes minerals such as pyroxenes, phlogopite, feldspars, and nepheline; the accessory mineral suite often features apatite, magnetite, pyrochlore, monazite, bastnäsite, fluorite, and zircon. Carbonate rocks of this type may occur as intrusions (stocks, sills) and, less commonly, as effusive lava flows or breccias.

Economic significance: Carbonatites are among the most important sources of rare earth elements (REEs), niobium, and tantalum, with minerals such as bastnäsite and monazite hosting REEs and pyrochlore hosting niobium and tantalum. Phosphate minerals provide additional phosphorus; other minerals may contain uranium and thorium in trace amounts.

Genetic models: The origin is debated, but most models involve mantle-derived carbonatite liquids either produced by partial melting of carbonated mantle or by differentiation of alkaline silicate magmas. They commonly form in intracontinental rift zones or near mantle plumes and frequently occur in ring complexes or intracrustal reservoirs.

Distribution: Carbonatites occur worldwide, with major complexes in several continents. They are studied for their petrogenesis and for their economic mineralization; their distinctive carbonate-rich composition makes them easily distinguished from silicate-dominated rocks.