Paragenesis of allanite-(Y) and allanite-(Ce) in tourmalinites of the Severny massif (Chukotka) and relationship between yttrium and lanthanides in allanite

Alekseev V. I., Marin Yu. В., Gembitskaya 1. M.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 6. P. 83-93

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Language: Russian


Morphology, optical properties and composition of allanite-(Ce) and allanite-(Y) have been studied for these minerals from rare-metal tourmalinites of the Severniy Massif in Chukotka. Composition and structure of host metasomatites, associations of rock-forming and accessory minerals were investigated also. One of obtained result is the conclusion about hydrothermal origin of both allanite species. There have been revealed the partial replacement of allanite-(Y) by allanite-(Ce), and detected metasomatic rims of 2—10 m width enriched in LREE around allanite-(Y). The degree of isomorphic substitution for Y+HREE and LREE in allanite-(Y) is estimated 16 %, in averages, whereas the maximum value of the ratio (Y+HREE)/LREE does not exceed 0.25. The assumption is made that transition of allanite-(Y) into allanite-(Ce) might be caused by an increase of acidity with decreasing water fluid temperature at the late stage of the hydrothermal process.

Key words: allanite-(Y), allanite-(Ce), yttrium, lanthanides, paragenesis, isomorphism, tourmalinite, Chukotka.