ИСТИНА

The distribution of rare-earth elements, Y and Sc between the aluminosilicate (L) and salt aluminofluoride (LF) melts in the Li-bearing granite system with high contents of fluorine has been experimentally studied. In the investigated Si-Al-Na-K-Li-F-H-O system the phase equilibrium of the aluminosilicate (L) and aluminofluoride salt (LF) melts is stably reproduced at the temperature of 800 °C , pressure of 1 and 2 kbar and a water content from 2,5 to 15 weight %. Among the main components of Na, Li, Al and F are predominantly distributed into the fluoride phase, and K, Si and O - into the silicate phase. Phase relationships and the contents of the main components and F in the solid products of the experiments were studied with the help of the electron microscope and microprobe Superprobe JSM-6480 LV and Superprobe JXA-8230. An analysis of the contents of rare-earth elements and Li in quenched melts and fluids was carried out by mass spectrometry ICP-MS2000 instrument (apparatus of the Lomonosov Moscow State University). It was shown that REE, Y and Sc with large partition coefficients Kp (LF / L) are distributed in favor of the fluorine- and lithium-rich melt, as compared to a silicate melt (which agrees with the known data [1,2]), and with larger Kp (LF / Fl) in comparison with the aqueous fluid (Fl). When studying the distribution of REE, Y, and Sc between coexisting aluminosilicate and salt melts, it was found that the behavior of REE, Y, and Sc essentially depends on pressure. The partition coefficients of REE Kp (LF / L) decrease by a factor of 5-10 with a pressure increase from 1 to 2 kbar. The partition coefficients between the melts decrease monotonically from light to heavy REE, both at 1 and at 2 kbar, forming a small maximum by Gd, i.e. when going from light to heavy REE. There is an increase in Kp (LF / L) with an increase in the water content in the system from 2,5 to 15 weight %. Thus, the rare earth elements proved to be much more sensitive to the processes occurring in the system than the main components. For the first time, a clear effect of REE partitioning between immiscible silicate and salt melts is found, depending on the pressure and water content of the system. Work is supported by RFBR-16-05-00859 [1]Gramenitskiy & Shchekina (2005) Geochem.Int. 43, №1, 45-59 39-52.[2]Veksler et al.(2005) Geochim.Cosmochim. Acta 69, №11, 2847-2860