Lanthanide mineral allanite

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). 

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. 

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). 

Allanite is a complex, lanthanide-concentrating mineral of generalized... 

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