Fluorine Controls Mineral Assemblages of Alkaline Metasomatites

In the Khibiny and Lovozero alkaline massifs, there are numerous xenoliths of so-called ‘aluminous hornfelses’ composed uncommon mineral associations, which, firstly, ultra-aluminous, secondly, highly reduced. (K,Na)-feldspar, albite, hercynite, fayalite, minerals phlogopite-annite cordierite-sekaninaite series, corundum, quartz, muscovite, sillimanite, andalusite rock-forming minerals. Fluorite, fluorapatite, ilmenite, pyrrhotite, ulvöspinel, troilite, native iron characteristic accessory The protolith these rocks is unknown. We studied in detail petrography, mineralogy, chemical composition believe that hornfelses were formed as a result metasomatic influence foidolites. main reason for formation an unusual aluminous association high mobility aluminum promoted by fluid expelled from foidolites Na-Al-OH-F complexes. Thus, it fluorine controls and, consequently, associations metasomatites. gain alkalis to was intense crystallization (K,Na)-feldspar. As result, SiO2 deficiency formed, Si-poor, Al-rich silicates and/or oxides crystallized.