The phase relations in the Si-Al-Na-K-Li-F-H-O model granite system were studied experimentally at T=800, 700°C and P=1 and 2 kbar, as well as at T=600, 550, 500 and 400°C and P=1 kbar and different water content from 2 to 50 wt.%. It is shown that two immiscible melts are formed in the system – aluminosilicate (L) and salt alkali-aluminofluoride (LF) in the presence of Li in liquidus conditions. The experiments were carried out on a high gas pressure unit in the IEM RAS. It is shown that at T=800°C, P=1 and 2 kbar and water content >10 wt.% equilibrium in the system are three phases: L, LF and fluid (Fl). At 700°C, cryolite (Crl), begins to crystallize from the salt melt. At 600°C, quartz (Qtz) crystallizes from the aluminosilicate melt, the equilibrium phases are: L, LF, Crl, Qtz. At T=500°C from L crystallizes Qtz, Na and K aluminofluorides and polylithionite. Сrystals of cryolite and elpasolite are formed in the salt melt. In this case, the residual salt melt enriched with Li and REE is preserved. At 400°C, LF completely crystallizes, and L is in a metastable state in the form of glass. It is found that REE, Sc, Y and Li accumulate in the salt melt up to 500°C with separation coefficients >>1. At T=500 and 400°C, REE and Sc are part of the crystal phases. Sc partially replaces Al in fluorides and micas. REE most often forms its own fluoride phases of the LnF3 type.
Congratulations, I find your work very interesting.
I would like to ask you if you have studied the behaviour of HFSE? It would be very interesting to know how they are partitioned into the two immiscible melts.
Best regards
José Francisco Molina
I thank you for your interest in the article.
Yes, we studied the distribution of rare earth elements, lithium, scandium, and yttrium between three phases: the aluminosilicate melt, the salt fluid, and the water fluid. It turns out that most of the rare earth elements are distributed in the salt melt (the separation coefficients are much greater than 1) just like yttrium and scandium, lithium, but scandium behaves somewhat ambiguously, is also distributed in the aluminosilicate melt. In the silicate melt, REE enters one or two orders of magnitude less, and the smallest number of elements is separated into the fluid, the concentrations are measured by ppb values.
If you have any more questions, I can email you aleks7975@yandex.ru reply and send you the works you are interested in.
Have a nice day.
Aleksandra.
I was wondering if you have investigated the partitioning between the immiscible melts of other elements, such as Th, U, Zr, Nb and Ta, which can lead to the concentration of very interesting mineral phases such as zircon, niobates, tantalates, etc.
Best regards
José Francisco Molina
The HFSE group also includes scandium and yttrium, I wrote immediately on those that we studied specifically for these experimental conditions. We have not worked with thorium and uranium, although it would certainly be very interesting, but according to E. N. Gramenitsky, T. I. Shchekina and V. N. Devyatova (2005), similar studies were conducted to study the distribution of tantalum, niobium, zirconium and hafnium. They all have a high affinity for fluorine, the ability to form complexes. Tantalum, niobium, zirconium, and hafnium are concentrated in the silicate melt. This distribution depends on the ratios of the principal components and varies differently for each of them. If lithium is introduced into the system, which leads to the formation of a salt fluoride melt, this significantly brings the hafnium and zirconium contents in the co-existing phases closer together compared to the higher contrast ratios in the silicate melt and cryolite. The separation coefficients approach one. There are many more pitfalls, but the main thing is that these elements are mainly distributed in the silicate melt. Specifically, we did not observe mineral fachs, for example, zircon, etc. Perhaps these are not the experimental conditions for such studies.
If you have any more questions, I will be happy to answer them.
Best wishes,
Aleksandra.
Thank you very much for your valuable information and for the paper you have sent me.
Best wishes
José
