Abnormally high-hafnium zircon from rare-metal pegmatites of the Vasin-Mylk deposit, Kola Peninsula

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Marco E. Ciriotti
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Abnormally high-hafnium zircon from rare-metal pegmatites of the Vasin-Mylk deposit, Kola Peninsula

Messaggio da Marco E. Ciriotti » dom 17 mar, 2019 12:13

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Referenza:
▪ Kudryashov, N.M., Skublov, S.G., Galankina, O.L., Udoratina, O.V., Voloshin, A.V. (2019): Abnormally high-hafnium zircon from rare-metal pegmatites of the Vasin-Mylk deposit (the northeastern part of the Kola Peninsula). Chemie der Erde, 79, (in press).

Abstract:
The deposit Vasin-Mylk is located in NE Kola Peninsula and represents the pegmatites of Li-Cs-Ta specialization (LCT-type). The studied zircon grains from aplitic zone of pegmatites contain av. 0.34-0.45 apfu of Hf, while the rims of grains contain 0.52-0.54 apfu Hf and correspond to hafnon. Zones with high hafnium content are brighter in BSE and CL comparing to central parts of crystals. The crystallization temperatures of high-Hf zircon were estimated as about 550 °C using Ti-in-zircon thermometer. A significant change in crystallization conditions led to isomorphic substitution of Zr by Hf to form hafnon. This change is related to precipitation of aluminous minerals (spodumene, lepidolite) from alumina-oversaturated melt, combined with flux elements (B, Li and F) contributed to the strong fractionation of the Zr/Hf ratio and crystallization of high-Hf zircon at the late («hydrothermal») stage of rare-metal pegmatite evolution. During this stage KDHf between zircon and granitic melt increases rapidly.
Marco E. Ciriotti

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