Fluorides and fluorcarbonates in rocks of the Katuginsky complex (East Siberia) as indicators of geochemical conditions of the mineral forming process
Savel'eva V. В., Bazarova E. P., Khromova Ε. Α., Kanakin S. V.
Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 2. P. 1-19
Chemical composition and parageneses of fluorides and fluorcarbonates have been studied in rocks of the Katuginsky complex bearing the unique deposit of REE-Nb-Ta ores with cryolite. Mineral and chemical composition of these rocks correspond to biotite, biotite-amphibole, arfvedsonite and aegirine-arfvedsonite granites, which in the earlier works were regarded as granite-like metasomatites. Aegirine-arfvedsonite granites contain the cryolite-gagarinite paragenesis reflecting the depletion of the mineral-forming media by Ca, together with enrichment in Na and F. Arfvedsonite granites are characterized by intergrowths of yttrofluorite with fluocerite and gagarinite, indicating the relative enrichment in Ca, with low CO2 concentration. Association of fluorite with titanite, apatite and monazite, characteristic for biotite granites, indicates, in its turn, an elevated concentration of Ca in the system and moderate concentrations of fluorine and phosphorus. In composition of biotite-amphibole granites, annite is replaced by riebeckite, and albite developes over microcline, there appear also neighborite, coulsellite, gagarinite, fluocerite and tweitite-(Y), which indicates the influence on the biotite granites of the moderately alkaline fluoride-sodium solutions with low concentration of Ca.
Key words: granite, fluorite, yttrofluorite, gagarinite, cryolite, bastnäsite, metasomatism.