Thank you Martin, it is true. In particular, we found fluorophlogopite in benmoreitic Etnean lavas, but only inside lava bubble and it was covered by SiO2-rich glass. So, fluorophlogopite nucleated and grew during sin- post-eruptive conditions due to exsolution of HF and deposition of SiO2 due to the reaction of SiF4 and H2O.

More recently, we have found a similar process in coeval lava flows on the lower SW flank of Mt. Etna (cf. Mazziotti Tagliani et al. 2012)

Minor contact features between Proterozoic carbonatites in S Greenland (Qassiarssuk) can show multiple cm-scale tubes cutting vertically for metres as pipes through undeformed coherent foliated granitic gneiss, and now filled with carbonate/carbonatite pipes. The process is unknown, but absence of fracturing and damage to the gneiss suggests this could have been achieved by acid dissolution: again there was high fluorine content indicated by modal fluorite, plus fluorapatite. So I would say yes HF was likely as a fluid in that system. Background paper Tom Andersen, Mineralogical Magazine 61, 499-513 (1997): outcrops of interest near to locations 48 and 14 in Figure 1 of that paper.

The formation of greisens (i.e., F-rich hydrothermal alteration zones) around cooling plutons is pretty strong evidence for the presence of orthomagmatic F-rich fluids in certain environments. Here is a reference to a recent paper exploring the role of HF in aqueous fluids similar to those that form greisens around peraluminous plutons (e.g., Sn-W-Mo-granite systems).

Experimental study of mineral equilibria in the system K2O(Li2O)-Al2O3-SiO2-H2O-HF at 300 to 600 degrees C and 100 MPa with application to natural greisen systems

Author(s): Shapovalov, YB (Shapovalov, Yu B.)[ 1 ] ; Setkova, TV (Setkova, T. V.)[ 1 ]

Source: AMERICAN MINERALOGIST Volume: 97 Issue: 8-9 Pages: 1452-1459 DOI: 10.2138/am.2012.3949 Published: AUG-SEP 2012

Times Cited: 0 (from Web of Science)

Cited References: 37 [ view related records ] Citation MapCitation Map

Abstract: We present the results of experimental studies on mineral and phase transformations in the model system K2O(Li2O)-Al2O3-SiO2-H2O-HF at 300 to 600 degrees C and 100 MPa using the method of univariant assemblages. The phase diagrams involve equilibrium curves among topaz, andalusite, muscovite, pyrophyllite, AlF3, and KnAlF3+n built from our experiments, which have allowed us to determine the topaz stability field. Topaz is stable in solutions with HF concentrations from 3.10(-3) to 8.10(-1) m and with KF concentrations lower than 7.5.10(-3) m. As temperature increases, topaz becomes stable at higher HF concentrations.

Application of the results to the Akchatau greisen W-Mo deposit provides an explanation of the observed zonation as a manifestation of metasomatic processes and imposes constraints on the mechanism and conditions of formation of the Akchatau deposit as well as on the compositions of the F-rich fluids participating in the greisenization.