Fine-grained petalite and spodumene dykes in the Stankuvatske Li-deposit, Ukrainian Shield: products of tectono-metamorphic recrystallisation

The Palaeoproterozoic (similar to 2.0-1.8 Ga) Stankuvatske Li deposit (Ukrainian Shield, Central Ukraine) represents an uncommon case of recrystallised, fine-grained petalite +/- spodumene meta-pegmatite dykes with LCT affinity hosted in amphibolites and meta-ultrabasic rocks. The meta-pegmatite dykes show remnants of primary, pre-metamorphic zoning, with dominant magmatic albite, K-feldspar, quartz, Li-phases (petalite, spodumene, rarely triphylite and montebrasite), and accessory muscovite, fluorapatite, columbite-(Fe), tantalite-(Fe), cassiterite, Ta-rich rutile, zinco- and ferronigerite, gahnite, pyrite, sphalerite and zircon. The parental magma of the meta-pegmatites was peraluminous, and enriched in Li and P, though relatively poor in B and F during the late-magmatic stage. Metasomatic reactions between residual pegmatite magma and (ultra)basic country rocks resulted in the precipitation of holmquistite, triphylite, fluorapatite, tourmaline and Rb-Cs-rich biotite. Secondary generations of fine-grained petalite, spodumene, albite and K-feldspar were formed during post-magmatic stages, i.e. during hydrothermal-metasomatic alteration and/or subsequent tectonometamorphic recrystallisation of the primary pegmatites. The initial subsolidus metasomatism of primary feldspars took place in alkaline conditions as a result of Na (partly K) for Li exchange. The presence of fibrolitic sillimanite and chrysoberyl, together with the scarcity of muscovite and (OH,F)-bearing minerals, point to metamorphic recrystallisation of the former Li-rich granitic pegmatites at relatively high-temperature and medium-pressure (similar to 600 +/- 50 degrees C; similar to 0.3-0.4 GPa) conditions.