Behavior of rare-earth elements during crystallization of model granite  system  with  water  and  fluorine

Shchekina, T.I.; Zinovieva, N.G.; Rusak, A.A.; Khvostikov, V.A.; Alferyeva, Y.O.; Kotelnikov, A.R.

Авторы: Shchekina T.I., Zinovieva N.G., Rusak A.A., Khvostikov V.A., Alferyeva Ya O., Kotelnikov A.R.
Журнал: Experiment in GeoSciences
Том: 27
Номер: 1
Год издания: 2021
Первая страница: 150
Последняя страница: 154
Аннотация: The behavior of rare-earth elements (REE), Y, Sc in a model granite system Si-Al-Na-K-Li-F-O-H with a limiting fluorine content at temperatures from 800 to 500 °C, a pressure of 1 kbar has been studied. Starting from 800 °C, when a region of liquid immiscibility appears in the system, all rare-earth elements are predominantly concentrated in the LF saline aluminofluoride melt in comparison with the silicate one. The partition coefficients between salt and aluminosilicate melts are much higher than KDREE (LF/L) >> 1. Rare-earth elements do not form their own phases in the silicate melt. With a decrease in temperature down to 500 °C, REEs continue to accumulate in the residual molten salt globules filling the interstitiums between the K-Na- aluminofluorides crystallizing in them. At temperature below 500 °C, the salt melt crystallizes, and REE, Y, Sc form fluoride compounds of the LnF3 type (analogue of fluocerite CeF3) or (Na,K)3LnF6 (analogue of gagarinite NaCaYF6). Only scandium from the considered group of elements shows a tendency to enter the structures of other phases crystallizing in the system, partially replacing Al in cryolite (Na, K)3(Al, Sc)F6 and Li-mica, similar to polylithionite KLi2(Al, Sc)Si4O10(F,OH)2. At 800 and 750 °C, a positive correlation is observed between the separation coefficients of REE, Y, Sc, and Li. The significant accumulation of REE in residual salt melts rich in volatile components (H2O and F) indicates a possible mechanism for the concentration of REE, Y, and Sc in granite massifs at the last stages of their differentiation and in pegmatites.
Добавил в систему: Русак Александра Андреевна

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Behavior of rare-earth elements during crystallization of model granite system with water and fluorineстатья

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