Carbonatite deposits

Current theories on their genesis revolve around a mechanism of mass gas transfer of material rich in carbonate derived from the upper mantle deep within the earth. The three most significant commercial carbonatite deposits are at Mountain Pass, California in the U.S.A., Palabora in South Africa and Paotou, Inner Mongolia in the Peoples Republic of China, see Figure 4. 

Carbonatites may or may not be associated with alkaline igneous complexes. Calcite and/or dolomite can be present in these carbonatites. Magnetite is very commonly associated with igneous apatite in carbonatite deposits. 

The element is found in niobite (or columbite), niobite-tantalite, parochlore, and euxenite. Large deposits of niobium have been found associated with carbonatites (carbon-silicate rocks), as a constituent of parochlore. Extensive ore reserves are found in Canada, Brazil, Nigeria, Zaire, and in Russia. 

Occurrence. Niobium and tantalum usually occur together. Niobium never occurs as the metal, ie, ia the free state. Sometimes it occurs as a hydroxide, siUcate, or borate most often it is combiaed with oxygen and another metal, forming a niobate or tantalate ia which the niobium and tantalum isomorphously replace one another with Htde change ia physical properties except density. Ore concentrations of niobium usually occur as carbonatites and are associated with tantalum ia pegmatites and alluvial deposits. Principal niobium-beariag minerals can be divided iato two groups, the titano- and tantalo-niobates. 

Intrusive Deposits. Deposits included in the intmsive deposit type are those associated with intmsive or anatectic rocks of different chemical composition, eg, alaskite, granite, monzonite, peralkaline syenite, carbonatite, and pegmatite. Examples include the uranium occurrences in the porphyry copper deposits such as Bingham Canyon and Twin Butte in the United States, the Rossing Deposit in Namibia, and Ilimaussaq deposit in Greenland, Palabora in South Africa, and the deposits in the Bancroft area, Canada (15). 

Carbonatite ores are mainly composed of calcite, dolomite and phosphates as the main gangue minerals. The beneficiation process for pegmatites containing pyrochlore mostly includes gravity preconcentration. Such deposits are common in Africa (Kongo, Madagascar). 

Metasomatic deposits are altered albite and granatoids. These are low-grade ores. Of economic interest is the carbonatites, which contain up to 1% combined Ta/Nb. 

Bastnaesite belongs to the carbonatite group of minerals that contain REOEs. Beside the cerium group of elements, bastnaesite also contains yttrium and europium. Typically, it contains 65-75% REOE. Bastnaesite is usually found in pegmatites, carbonatite and hydrothermal ore bodies in alkaline gangue minerals. Because it is poor chemically and stable, it is not found in mineral sand deposits. 

Floatability of bastnaesite found in barite-fluorite ores is extremely poor using either fatty acid flotation or sodium oleate. Research work conducted on an ore from Central Asia showed that the floatability of bastnaesite improved significantly after barite preflotation [5]. The flotation of bastnaesite from a carbonatite ore improved with the use of oleic acid modified with phosphate ester. The flotation of bastnaesite from deposits ofpegmatitic origin can be successfully accomplished with several types of collectors, including tall oil modified with secondary amine, and tall oil modified with petroleum sulphonate-encompassing group. 

Besides the conventional uranium resources, there are also the so-called unconventional uranium resources , which are defined as deposits with very low uranium content, from which uranium is typically only recoverable as a minor by-product. These unconventional uranium resources are obtained from the extraction of phosphates, non-ferrous ores and carbonatites, as well as black schist and lignite. It has to be noted that the distinction between conventional and unconventional resources is not entirely clear cut, but is, instead, somewhat transitional. 

Later (Zotov 1980, 1989 Korzhinskii et at. 1984 Marakushev et at. from 2002 up to 2006), it was shown that transmagmatic fluids are able to transport ore metals whose portion may be predominant in endogenic deposits as for example in R-Pd-Cu-Ni sulfide deposits (same ref.), apatite deposits of alkali (Zotov 1989) and alkali-carbonatite (Seredkin et at. 2004) magmatic massifs. This concept is essentially useful as an application for understanding of genesis of big endogenic ore deposits (Zotov 1980). 

Helium surveys could be considered, therefore, to be effective in locating faults and permeable zones, which might be the sites of certain types of mineral deposits. Examples are given of He anomalies associated with carbonatites, Au-quartz veins, Pb-Zn-Ba veins and Cu-pyrite veins (Eremeev et al., 1973), stockwork Mo-deposits (Ovchiimikov et al.,... 

The U.S. Geological Survey was scheduled to publish a revised study of U.S. thorium resources in August 1979. Partial results of this study, which cover most of these resources but do not include the beach placers of Florida, Georgia, and the Carolinas, were presented orally by Staatz [S5] of the U.S. Geological Survey in 1978. Table 6.14 lists the types of deposit, the principal districts in which potentially economic thorium-bearing deposits have been found, the principal thorium minerals, and estimates of thorium reserves and resources. Thorium from the vein deposits, the first type, could be produced for less than 30/lb. Thorium is the principal salable product in these deposits. Thorium could be coproduced with other elements from disseminated deposits, massive carbonatites, and placers the amount of thorium that might be produced from them, and its cost, depends on the marketability of the other minerals that occur with the thorium. 

Apatite from mafic systems, irrespective of their relation to ore-systems, displays considerable variability and overlap on a plot of Ce-Mn-Fe (Fig. 3c), but apatite from systems not associated with ore-deposits may have lower concentrations of Mn. Carbonatites appear to have considerable exchange of Ce for Fe (Fig. 3d), a substitution that may require charge balance depending on the oxidation state of Fe substituting in the apatite. 

The Mount Weld carbonatite dates from the Proterozoic (approximately 2025 Ma ago) and is emplaced in the Yilgarn Craton (Hoatson et al. 2011). The carbonatite is covered by a thick lateritic soil, which in its turn is covered by lacustrine and alluvial sediments (Lottermoser 1990). The Mount Weld deposit occurs in the weathered layer. 

The Nolans Bore deposit (Amnta Region, NT) is located in a zone which also contains the Mud Tank Carbonatite, Mordor Igneous Complex, and several tin- and tantalum-bearing pegmatites (Fig. 2.15). The deposit was discovered in 1995 (Arafura Resources 2014). 

Other carbonatite-related REE-deposits in Central and East Africa are, for instance ... 

It is a vein type deposit, which is hosted within, and is genetically related to, a carbonatitic alkaline complex. The deposit is very similar to the Californian Mountain Pass deposit. The similarities are the high concentrations of bastnaesite and barite, low niobium content, and the presence of sulphides (Wang et al. 2001). It has proven reserves of 0.4 million tons of ore grading at 2 % REE oxides. The discovery of the deposit was described by Pu (1988). The age of the carbonatites related to the deposit is 27.8-40.3 Ma (Cheng et al. 2003 Mindat.Org 2015). 

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