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| Carbonatite | |
|---|---|
| Name | Carbonatite |
| Caption | Carbonatite intrusive rock sample |
| Type | Igneous rock (carbonate-rich) |
| Composition | Calcite, dolomite, ankerite, rare earth minerals |
| Primary minerals | Calcite; Dolomite; Ankerite; Apatite; Nepheline; Pyrochlore |
| Country | Examples: Kenya; Brazil; India; Canada; Norway |
| Region | Examples: East African Rift; Gabon; Oldoinyo Lengai; Siilinjärvi; Bear Lodge Mountains |
| Notable localities | Mount Aucanquilcha; Gärdsjö; Lofdal; Sørensenfjella; Maoniuping |
Carbonatite is a rare, carbonate-rich igneous rock dominated by carbonate minerals such as calcite or dolomite. It occurs as intrusive bodies, extrusive flows, and hydrothermal veins, and is closely associated with alkaline magmatism, rift environments, and unusual mantle processes. Carbonatites are economically important as sources of rare earth elements, niobium, phosphorus, and fluorine, and their study informs models of mantle metasomatism, crustal evolution, and volatile cycling.
Carbonatite occurrences were recognized in classic localities like Ol Doinyo Lengai and Mountain Pass (mine), and have been studied in the context of regional complexes such as Forrestania, Phalaborwa, Pico de Ana Ferreira, Kola Peninsula, and Mafic–Ultramafic complexes in South Africa, Canada, United States, Brazil, Norway, China, and Russia. Petrologists and economic geologists from institutions including United States Geological Survey, British Geological Survey, Smithsonian Institution, and universities such as University of Cambridge, Massachusetts Institute of Technology, University of Oxford, and University of Nairobi have contributed to mapping, geochemical analysis, and modeling. Historic investigations by scientists affiliated with Geological Society of America, International Union of Geological Sciences, Society of Economic Geologists, and national surveys led to classification schemes used in mineral exploration and academic research.
Geologists link carbonatite genesis to processes observed at tectonic settings like the East African Rift, Rio Grande Rift, Baikal Rift Zone, Red Sea Rift, and intraplate provinces such as the Canadian Shield and Precambrian cratons (e.g., Kaapvaal Craton, Yilgarn Craton, Superior Province). Field studies often involve mapping at complexes such as Gabon (Mounana), Namyata, Alnö, Kibaran Belt, and Gardiner Complex. Geochemical and isotopic investigations utilize laboratories at Lamont–Doherty Earth Observatory, Geological Survey of Finland, Geological Survey of India, Université Paris-Sud, and Peking University to analyze major-element, trace-element, and radiogenic-isotope signatures. Petrogenetic models compare fractional crystallization, liquid immiscibility, low-degree partial melting, and mantle metasomatism derived from studies by researchers associated with Stanford University, ETH Zurich, University of Western Australia, and University of Toronto.
Mineralogists identify primary phases including calcite, dolomite, ankerite, and accessory minerals such as apatite, pyrochlore, barite, magnetite, and bastnäsite at sites like Siilinjärvi, Araxá, Morro do Ferro, Khibiny, and Lofdal. Trace-element enrichment patterns commonly show elevated concentrations of light and heavy rare earth elements, niobium, phosphorus, fluorine, and sometimes uranium or thorium, with key deposits reported at Mountain Pass (mine), Araxa, Pitinga, Khibiny, Nolans Bore, and Bayovar. Geochemical tools from institutions like Geological Survey of Canada, USGS, CSIR (South Africa), and CSIRO employ mass spectrometry (e.g., TIMS, ICP-MS, SIMS) and petrographic techniques to determine partition coefficients, melt inclusion compositions, and isotope ratios (Sr, Nd, Pb, C, O) for interpretations tied to works published in journals of Geological Society of America, Nature, and Science.
Well-known carbonatite provinces include the East African Rift complex with Ol Doinyo Lengai (unique natrocarbonatite lava), the Alnö Complex in Sweden, the Phalaborwa Complex in South Africa, the Monsieur Lake Complex in Canada, and the Bayan Obo deposit in Inner Mongolia. Other notable localities are Maoniuping, Gabon (Mounana), Mount Weld, Lofdal, Siilinjärvi, Gâvres, Fen Complex, Bear Lodge Mountains, Kabwe, and Mwinilunga. Distribution studies integrate remote sensing data from Landsat, Sentinel-2, and geophysical surveys by organizations such as USGS, British Antarctic Survey, and national geological surveys to prioritize exploration in provinces like Amazonia, Central Africa Rift System, Siberia, and Deccan Traps margin settings.
Carbonatite-associated deposits provide significant resources: rare earth elements at Bayan Obo, Mount Weld, Nolans Bore, Mountain Pass (mine), and Araxa; niobium at Araxa and Catalão; phosphate at Phalaborwa and Morro do Ferro; and fluorite or barite at multiple complexes. Mining companies such as Molycorp, Lynas Corporation, Rio Tinto, Anglo American, Vale S.A., and China Northern Rare Earth Group have invested in carbonatite-hosted deposits. Industrial applications link to manufacturers and sectors represented by Tesla, Inc. (magnets), BASF (specialty chemicals), General Electric (wind turbines), Boeing (aerospace alloys), and fertilizer producers. Policy and trade considerations involve entities such as World Trade Organization, European Union, United States Department of Commerce, and national ministries overseeing mineral resources.
Radiometric dating (U-Pb, Ar-Ar, Rb-Sr, Sm-Nd) from sites in the Kola Peninsula, Kaapvaal Craton, Amazonian cratons, Siberian Platform, North China Craton, and Laurentia shows ages ranging from Archean through Phanerozoic, with prominent pulses in the Proterozoic and Cenozoic. Tectonic interpretations relate carbonatite emplacement to continental rifting (East African Rift), mantle plume events (Icelandic plume comparisons, Siberian Traps temporal associations)), and post-orogenic extension in belts such as the Variscan Orogeny and Caledonian orogeny domains. Formation models debated in the literature include low-degree partial melting of a carbonated mantle source, liquid immiscibility from alkaline silicate magmas, and extreme fractional crystallization in closed systems—positions advanced by researchers at University of Edinburgh, University of Bergen, University of Western Ontario, and Indian Institute of Science.
Weathering of carbonatite bodies produces secondary mineral assemblages (e.g., supergene phosphates, rare earth oxide concentrates, secondary carbonate phases) observed at Mount Weld, Nolans Bore, Phalaborwa, and Bayovar. Acidic and alkaline groundwater interactions near mines can mobilize radionuclides and heavy metals, prompting environmental studies by Environmental Protection Agency branches, UNEP, World Health Organization, and academic groups at University of Cape Town, University of Queensland, and McGill University. Remediation and tailings management strategies employ expertise from International Council on Mining and Metals, ICMM, national regulators, and consulting firms. Geochemical modeling of CO2 fluxes, carbon sequestration potential, and volatile budgets in carbonatite systems involves collaborations with climate and geoscience centers like IPCC working groups and university departments engaged in carbon cycle research.
Category:Igneous rocks