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

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Title: Controls on chemical evolution and rare element enrichment in crystallising albite-spodumene pegmatite and wallrocks: Constraints from mineral chemistry
Authors: Barros, RenataKaeter, DavidMenuge, JulianŠkoda, Radek
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Date: Jan-2020
Online since: 2020-09-08T15:11:47Z
Abstract: 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.
Funding Details: European Commission - European Regional Development Fund
Science Foundation Ireland
metadata.dc.description.othersponsorship: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
Type of material: Journal Article
Publisher: Elsevier
Journal: Lithos
Volume: 352–353
Start page: 1
End page: 19
Copyright (published version): 2019 Elsevier
Keywords: Leinster pegmatite beltAlbite-spodumene pegmatitePegmatite zonationAlbitisation
DOI: 10.1016/j.lithos.2019.105289
Language: en
Status of Item: Peer reviewed
Appears in Collections:Earth Sciences Research Collection
ICRAG Research Collection

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