Acta Musei Moraviae

Mineral assemblages of the phosphate nodules from the granitic pegmatite at Cyrilov near Velké Meziříčí, Moldanubicum; part I-primary and exsolution phases

Granitic pegmatite near Cyrilov, the type locality of cyrilovite belongs to the beryl-columbite-phosphate subtype of the REL-Li type, despite the absence of the beryl. The primary phosphates and associate minerals occur in two assemblages: i) zwieselite nodule minerals – zwieselite, uraninite, ilmenite, ixiolite and Nb-rich ferberite and ii) graftonite nodule minerals – graftonite, sarcopside, wolfeite, triphylite, harrisonite, monazite-(Ce) and xenotime-(Y). The triphylite is completely altered to ferrisicklerite and heterosite. Crystallization of zwieselite decreased the content of F in the melt; this allowed consequent graftonite crystallization. Graftonite crystallized as Li,OH-rich precursor. In the graftonite nodule assemblage, exsolution proceeds in (at least) two stages: i) a Li,OH-rich precursor unmixed to wolfeite, sarcopside I, graftonite II and to the precursor of triphylite and sarcopside II, ii) a further decrease of temperature induces an exsolution of triphylite and sarcopside II from they precursor. The genetic position of harrisonite is not clear. Subhedral monazite-(Ce) associated with wolfeite, graftonite II and sarcopside I and “worm”-like monazite-(Ce) from triphylite-sarcopside II intergrowths is rich in Nd (≤20,35 wt.% Nd₂O₃) and Sm (≤10,47 wt.% Sm₂O₃). Based on the chemical composition of primary phosphates and Nb–Ta–Ti–W oxides examined, the assemblage crystallize from Li-poor melt with moderate content of F and low degree of Fe/Mn and Nb/Ta fractionation.