Rare earth pegmatites

W.B. Simmons and E. W. Heinrich, Rare-earth pegmatites of the South Platte District, Colorado, Colorado Geological Survey, Denver, p. 131, (1980). 

Members of the columbite-tantalite family of minerals also often contain significant U along with rare earths, Fe, Ca and Th. The B site is either Nb or Ta. Like the pyrochlores, these minerals are associated with rare-earth pegmatites and are also known from placer deposits. Most of the compounds probably formed initially with U —most probably as a coupled substitution Ca -t-U for a trivalent ion. Oxidation occurs easily, however, and most specimens contain significant amounts of U. Those minerals which contain radioactive elements are usually metamict and require heating to develop crystallinity. 

Supergroup. The principal rock-types in the intrusion are syenites, granites and gabbros, and associated pegmatitic bodies hosting rare metal mineralization. Five distinct zones of rare metal mineralization have been identified as potentially economic. The Lake Zone is one of them and is characterized by its enrichment in the more valuable HREE (Eu, Tb, and Dy), relative to light rare earths (LREE, i.e.. La and Ce) (Palmer Broad 2007). 

Monazite, a rare-earth phosphate, is one of the most abundant rare-earth minerals. It occurs as an accessory mineral in granitic and metamorphic rocks, pegmatites, vein deposits, as a dendrital mineral in placer deposits and as a... 

Arden KM, Halden NM (1999) Crystallization and alteration history of britholite in rare-earth-element-enriched pegmatitic segregations associated with the Eden Lake Complex, Manitoba, Canada. Can Mineral 37 ... 

Pan Y, Breaks FW (1997) Rare earth elements in fiuorapatite. Separation Lake area, Ontario Evidence for S-type granite - rare-element pegmatite linkage. Can Mineral 35 659-671 Pan Y, Chen N, Weil JA, Nilges MJ (2002a) Election paramagnetic resonance spectroscopic study of synthetic fiuorapatite Part III. Stmctural characterization of sub-ppm-level Gd and Mn in minerals at W-band frequency. Am Mineral (in press)... 

Shmakin BM, Shiryaye V (1968) Distribution of rare earths and some other elements in apatites of muscovite pegmatites, eastern Siberia. Geochem Inti 5 796 Smith MP (1999) Reaetion relatiorrships in the Bayan Obo Fe-REE-Nb deposit Irmer Mongoha, China implicatiorrs for the relative stability of rare-earth element phosphates and fluorearbonates. Contrib Mineral Petrol 134 294-310. 

Amli R (1975) Mineralogy and rare earth geochemistry of apatite and xenotime from the Gloserheia granite pegmatite, Froland, southern Norway. Am Mineral 60 607-620... 

Pu G (1988) Discovery of an alkali-pegmatite carbonatite complex zone in Maoniuping, south-western Sichuan Province. Geol Rev 34(l) 86-92 (In Chinese, with English Abstract) Olson JC, Shaw DR, Pray LC, Sharp WN (1954) Rare-earth mineral deposits of the Mountain Pass District, San Bernardino County, California. USGS Prof Papta 261, 75 p Orris GJ, Grauch Rl (2002) Rare earth element mines, deposits, and occurrences. USGS open file report, 02-189, 174 p... 

Occurrence. The geochemistry of the rare earths indicates that they are usually present in the final crystallization processes of the magma. They are therefore found in pegmatite dykes in association with other elements of low abundance that also were too diluted in the principal stages of the magmatic crystallization to form their own... 

Economic sources of the rare earth elements are usually in pegmatites, or concentrated as resistant minerals in beach sands (e.g. monazite). Reviews of these sources are given by Neary and Highley (1984). 

Bastnasite (CeFCOs) - a fluorocarbonate of cerium containing 60-70% rare earth oxides (REO), including lanthanum and neodymium - is the world s major source of rare earths. Host rocks include carbonatite, dolomite breccia with syenite intrusives, pegmatite, and amphibole skam. Since 1985, the bastnasite production in China has increased very fast and has dominated the market from the 1990s to the present. 

Other rare elements are incompatible with the main elements in the solidified siH-cate melt. Ion radius and charge differ too much. These elements will be enriched in the melt, remaining when the silicates gradually solidify. They wiU be found in the coarse-grained pegmatites, rich in rare earths and minerals containing such elements as lithium, niobium and tantalum. 

Mineev, D. a. Epidote containing rare earths from pegmatites of the Middle Urals. Akad. Nauk SSSR Doklady 127, 865—868 (1959). 

Rubidium is not too rare in the earth crust, being more abundant than lead. As stone melts crystallized when the earth s crust was formed, rubidium followed potassium in all minerals, as the ionic radii of these two elements are very similar. Consequently there are no typical rubidium minerals. This has been discussed in Chapter 4, Geochemistry. LepidoHte, a hthium-rich mica, is an exception. In that mineral, rubidium can substitute for lithium to such a great extent that as much as 2.5% may be present. One such source is the pegmatite at Bemic Lake, Manitoba in Canada. From mines there, a rubidium-containing lepidolite fraction is obtained and separated as a by-product However, this is not a very profitable business. The demand for rubidium in the whole world is only about 2 tonnes per year and this quantity is obtained in a few hours at Bemic Lake [13.1]. This lepidolite is worked in chemical plants in the US. From the mixed alkali carbonates, rubidium is isolated as sulfate or chloride by advanced separation processes. 

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