Lanthanide mineral apatite

From the data in fig. 21.19 it can be seen that most minerals do not remove lanthanides effectively from silicate liquids (i.e., lanthanide D values are mostly less than unity). Exceptions are apatite (a lanthanide-concentrating mineral that is a common late-stage product of crystallization of mafic liquids) and garnet (which concentrates heavy lanthanides but not light lanthanides). In acid magmas, lanthanide minerals may precipitate these are discussed in later sections. Ca-rich clinopyroxenes and hornblendes (related to pyroxenes, but more compositionally complex) compete for lanthanides successfully against somewhat acidic lavas (Nagasawa and Schnetzler, 1971). 

The bastnaesite-synchisite series of lanthanide minerals can be considered in terms of stoichiometric ratios of RCO3F to CaCOj in proportions 1 0, 1 1, 2 1, and 3 2. The minerals of this series are much more rare than allanite or apatite but are fairly common in alkalic rock suites and in some metamorphic terrains. This mineral occurs in commercially important amounts in carbonatite associated with other alkalic rocks at Mountain Pass, California. The mineral is usually light-lanthanide rich, although rare heavy-lanthanide rich examples are known (fig. 21.28). 

Phosphate rock, mined widely throughout the world for its fertilizer value (see Fertilizers), in certain regions contains a few percent of lanthanides. For example, the apatite deposits in the Kola peninsula on the Russian/Finnish border. The Ln content is recoverable from the various processing residues, and because other Ln-containing minerals, such as loparite [12173-83-0], are also found there, the location suppHes a significant part of the demand in Eastern Europe. 

Erbium occurs in certain types of apatites, xenolime. and gadolinite. These minerals also are processed for their yttrium content as well as for other heavy Lanthanide elements. With liquid-liquid organic and solid-resin organic inn-exchange techniques, the separation of erbium from the other elements is favorable. 

Cations of the lanthanide elements also produce colours in some minerals through intra-electronic transitions within 4/orbitals (Adams, 1965 Bernstein, 1982). Absorption bands are usually sharp and weak, leading to pastel shades. Examples of such coloured minerals are monazite, bastnaesite, rhabdophane, xenotime, gadolinite, and certain apatites, calcites, scheelites and fluorites. As noted earlier, some rare earth-bearing minerals, notably fluorite and monazite, also display the alexandrite effect (Berstein, 1982 Schmetzer et al., 1980). 

Although early attempts to identify it in lanthanide ores were not successful, it has been detected at the level of 4 X 10 gkg in Congolese pitchblende. It has also been detected at a low level in apatite (10 g from 6milhon kg mineral), although it may have originated there from neutron irradiation of neodymium or by spontaneous fission of... 

Phosphate containing rock in certain areas contains a few-percent of lanthanides, e. g. the apatite deposits in the Kola peninsula in the Commonwealth of Independent States (C.I.S.). Loparite, a Nb-mineral containing rare-earths is also present and is the leading source of rare-earths for the C.I.S. [8]. 

Fleischer M, Altschuler ZS (1986) The lanthanides and yttrium in minerals of the apatite group - an analysis of the available data. N Jahrb Mineral Monatsh 467-480 Fleischer M, Mandarine JA (1995) Glossary of Mineral Species (7th ed). Mineral Record, Tucson, Arizona. Fortsch E, Freiburg IB (1970) Untersuchungen as mineralien der pyromorphit grappe. N Jahib Mineral Abh 113 219-250... 

The lanthanide abundance pattern for Shergotty (table 9, fig. 7) is unique among meteorites and indicates a complex prehistory in the Martian mantle from which they appear to have been derived, as basalts, by partial melting. The enriched pattern of the heavy lanthanides (Gd-Lu) resembles that of pyroxenes (the parent rocks appear to have been pyroxene cumulates). It provides no evidence that garnet was a residual phase in the source from which these basalts were derived, for, if so, the reciprocal pattern would be displayed. Leaching experiments show that most of the lanthanides are contained in accessory phases (whitlockite and apatite) rather than in the major mineral phases. 

Quantitative modelling has been less successfully applied to rocks cff more felsic composition, such as granodiorites, dacites, granites and rhyolites. This is principally due to the ubiquitous presence in these evolved rocks of minor mineral phases, such as sphene, allanite, apatite and zircon, whose lanthanide contents may account for a substantial fraction of the total rock budget. Thus Gromet and Silver (1983) found that sphene and allanite, in a granodiorite from the Peninsular Ranges, California, contained 80-95% of the lanthanide content of the total rock. Distribution coefficients are not well known for these phases and the abundances of these trace minerals are difficult to determine accurately. 

There are three groups of minerals in which the REE are found. Minerals in the first group contain major quantities of lanthanides. All of these are associated with crystallizations from magmatic mother liquors of pegmatic character (Topp 1965). Important examples are the minerals monazite and xenotime. The second group includes minerals with the REE as minor constituents. Many calcium minerals, such as apatite, are members of this group. Minerals in the third group contain the REE in the bipositive state in small isolated distributions. These are not used as sources of rare earths. 

Fig. 21.19. Typical values of lanthanide distribution coefficients for common, rock-forming minerals. Values for apatite inferred from analysis of Skaergaard intrusion (Paster et al., 1974) rest from phenocryst-matrix analyses (Schnetzler and Philpotts, 1970).

Because the lanthanides and yttrium are dispersed elements they are found mainly as trace constituents of common rocks. Within those rocks they occur partly as trace constituents of the major, rock-forming minerals and partly in accessory minerals in which the lanthanides are either essential constituents (e.g., monazite) or are concentrated (e.g., apatite). More than 100 different lanthanide and lanthanide-concentrating minerals are known. Most of these form from liquids that are highly differentiated chemically relative to common magmas. Such liquids are rich in a wide variety of elements that are trace elements in terms of their natural abundances but major constituents of the final dregs of liquid when magmas freeze. 

Placer deposits of potential future value as lanthanide ores invariably have the lanthanides present in common lanthanide or lanthanide-concentrating minerals (e.g., apatite, allanite, monazite, xenotime, zircon). Most pegmatites of potential value as ore have the lanthanides as common lanthanide-bearing minerals too (those previously mentioned plus fluorite). Alkalic rock complexes may produce commercially useful concentrations of common lanthanide-bearing minerals (e.g., apatite, perovskite) or rare ones (e.g., bastnaesite). 

---