Controls on chemical evolution and rare element enrichment in crystallising albite-spodumene pegmatite and wallrocks: Constraints from mineral chemistry

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Publikace nespadá pod Filozofickou fakultu, ale pod Přírodovědeckou fakultu. Oficiální stránka publikace je na webu muni.cz.
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BARROS Renata KAETER David MENUGE Julian F. ŠKODA Radek

Rok publikování 2020
Druh Článek v odborném periodiku
Časopis / Zdroj Lithos
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Citace
www https://doi.org/10.1016/j.lithos.2019.105289
Doi http://dx.doi.org/10.1016/j.lithos.2019.105289
Klíčová slova Leinster pegmatite belt; Albite-spodumene pegmatite; Pegmatite zonation; Albitisation
Popis Internal differentiation and consequent geochemical evolution in pegmatites are significant processes in the development of economically viable deposits of metal-bearing minerals. Albite-spodumene pegmatites, which represent important resources of Li and Ta worldwide, challenge the general rules of pegmatite petrogenesis as these are nearly homogeneous bodies with little or no intrusion-scale pegmatite zonation. Bulk intrusion concentrations of Li are in the uppermost range obtained by magmatic enrichment experiments, around 2 wt% Li2O, and extensive volumes of saccharoidal or platy albite are present. In Leinster, southeast Ireland, weakly zoned to homogeneous albitised spodumene pegmatites and their wallrocks were studied to compare mineral chemistry variations and understand the internal evolution of pegmatites, characteristics linked to the poor development of zonation, and links between internal evolution and pegmatite-wallrock interactions. Leinster pegmatites present mineralogical, textural and geochemical characteristics coherent with Li-saturation, and possibly supersaturation, prior to crystallisation. Weak border to centre zonation in the thickest bodies can be attributed to geochemically evolved initial melt, likely leading to nearly contemporaneous crystallisation throughout the intrusion and resulting in limited internal geochemical fractionation. Increased abundance of minerals bearing highly incompatible elements (e.g. columbite-group minerals and cassiterite) and network modifiers (e.g. phosphates) in albitite indicates it is a fractionation product from pegmatite crystallisation. Enrichment in incompatible elements B, Li, Rb, Cs and F in spodumene pegmatite exocontacts in different country rock types suggests unmixing of a hydrous fluid from the residual melt after the crystallisation of main pegmatitic assemblages, and that the H2O-rich component was mobilised into country rocks. (C) 2019 Elsevier B.V. All rights reserved.
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