Fine-grained petalite and spodumene dykes in the Stankuvatske Li-deposit, Ukrainian Shield

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Marco E. Ciriotti
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Fine-grained petalite and spodumene dykes in the Stankuvatske Li-deposit, Ukrainian Shield

Messaggio da Marco E. Ciriotti » ven 09 set, 2022 10:23

Prossima pubblicazione.

Referenza:
▪ Kurylo, S., Uher, P., Broska I., Lyzhachenko, N., Bondarenko, S., Gieré, R. (2022): Fine-grained petalite and spodumene dykes in the Stankuvatske Li-deposit, Ukrainian Shield: products of tectono-metamorphic recrystallisation. Mineralogical Magazine, 86, (in press).

Abstract:
The Paleoproterozoic (~2.0−1.8 Ga) Stankuvatske Li deposit (Ukrainian Shield, Central Ukraine) represents an uncommon case of recrystallised, fine-grained petalite  spodumene metapegmatite dykes with LCT affinity hosted in amphibolites and metaultrabasic rocks. The metapegmatite 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 investigated metapegmatites was peraluminous, and enriched in Li and P but 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 tectono-metamorphic recrystallization 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, as well as 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 (~600  50 °C; ~0.3−0.4 GPa) conditions.
Marco E. Ciriotti

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