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Assessment of magmatic vs. metasomatic processes in rare-metal granites: A case study of the Cínovec/Zinnwald Sn–W–Li deposit, Central Europe

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    0479233 - GLÚ 2018 RIV NL eng J - Journal Article
    Breiter, Karel - Ďurišová, Jana - Hrstka, Tomáš - Korbelová, Zuzana - Hložková Vaňková, M. - Vašinová Galiová, M. - Kanický, V. - Rambousek, P. - Knésl, I. - Dobeš, P. - Dosbaba, M.
    Assessment of magmatic vs. metasomatic processes in rare-metal granites: A case study of the Cínovec/Zinnwald Sn–W–Li deposit, Central Europe.
    Lithos. 292/293, November (2017), s. 198-217. ISSN 0024-4937. E-ISSN 1872-6143
    R&D Projects: GA ČR GA14-13600S
    Institutional support: RVO:67985831
    Keywords : rare-metal granite * Cínovec/Zinnwald deposit * rock textures * metasomatic processes * magmatic processes
    OECD category: Geology
    Impact factor: 3.857, year: 2017

    The Cínovec rare-metal granite in the eastern segment of the Krušné Hory/Erzgebirge formed in the final stage of the magmatic evolution of the late Variscan volcano-plutonic system known as the Teplice caldera. The granite is slightly peraluminous, enriched in F, Li, Rb, Cs, Nb, Ta, Sn, W, Sc and U, and poor in P, Mg, Ti, Sr and Ba. The uppermost part of the granite cupola hosts a greisen-type Sn–W–Li deposit. Borehole CS-1 permits to study vertical evolution of the pluton to a depth of 1597 m. A combination of textural and chemical methods was applied to whole-rock and mineral samples to identify the extent of magmatic and metasomatic processes during the differentiation of the pluton and formation of the deposit. The following genetic scenario is proposed: the intrusion of the zinnwaldite granite magma reached subvolcanic conditions and a hem of fine-grained porphyritic granite crystallized along the upper contact. Separation of the first portion of fluid from the oversaturated melt promoted explosive degassing and the origin of breccia pipes. Subsequently, the zinnwaldite granite magma crystallized simultaneously from the upper contact and the footwall inwards. The residual melt between the two crystallizing fronts became enriched in water and volatiles to reach second saturation. Segregated fluids escaped upwards, causing hydrofracturing of the overlying granite, while the water-poor residuum crystallized in situ in the form of mica-free granite. F- and Li-rich fluids invoked greisenization and created quartz–zinnwaldite veins. Alkalis liberated from feldspars destroyed during the greisenization induced local albitization in the uppermost part of the cupola and K-feldspathisation in its deeper part. The distribution of Sn and W was controlled by fluid processes, while Nb and Ta mainly crystallized from the melt. The results from Cínovec are universally applicable to shallow-intruded rare-metal granites regardless of A- or S-types of the primary magma.
    Permanent Link: http://hdl.handle.net/11104/0275231

     
     
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