While I am picking migmatites, I notice an absence of monazite in tourmaline rich ones. Tourmalines are well-developed idiomorphic, brown and can be clearly seen under x2.5 magnification. But in these rocks, monazite couldn't be found. Does it have a meaning chemically and also geologically? How should I use it or interpret it?
Dear Zehra,
What it often observed is the presence of apatite or xenotime while rock is devoid of monazite. In this case, ihis can be explained by the incorporation of both the Phosphorus and the REE in one mineral instaead of another. To me, the correlation of the presence of tourmaline and the absence of monazite is much more speculalive even if tourmaline may incorporate REE.
Sincerely,
What about apatite?, apatite and tourmaline are associated. Boron is fractionated with excess of phosporus
http://www.jgeosci.org/content/JCGS.806_Alfonso.pdf
Dear Zehra,
I think you should look at a chemical analysis of your rocks and check for P content. If you don't have enough P, than the absence of phosphates might be "normal" and you should look for geochemical origins of your question. This is related to the origin and evolution of original rock and fluids. Monazite, and also xenotime you must have in your samples, the question is in what amount and grain size. Is it possible to have REE depletion during migmatization?
F.
Dear Ferenc,
Thank you so much for your brief explanation. Your idea is promising for solution. It is needed to apply some chemical process to the samples. This will be the next step of my research.
Both minerals are usually associated with hydrothermal solution and alterations in pegmatite or in carbonatitie (mainly monazite). Monazites needs large concentration of REE (Ce, Nb, or Y) + P2O5 in the solution to be formed. So it is a typical mineral in carbonatite and some pegmatitie. Both should not be expected to be associated in the same rock, as both are chemically and mineralogically different
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