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Evidence of a water-rich silica gel state during the formation of a simple pegmatite

Published online by Cambridge University Press:  05 July 2018

R. Thomas  and
P. Davidson
R. Thomas*
Affiliation:
German Research Centre for Geosciences GFZ, Telegrafenberg D320, Potsdam, Brandenburg D-14473, Germany
P. Davidson
Affiliation:
ARC Centre of Excellence in Ore Deposits, University of Tasmania, Tasmania, Australia
*
*E-mail: rainerthomas@t-online.de
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Abstract

This study reports the discovery of inclusions, which are inferred to represent trapped primary silicate gels, in simple pegmatites genetically connected to the Precambrian Rønne granite of Bornholm Island, Denmark. These inclusions are randomly associated with more typical melt and alkali-carbonate-rich and bicarbonate-rich fluid inclusions. Their relationship to the latter and to the formation of the pegmatite bodies is discussed. The silicate gel inclusions become increasingly common towards the quartz cores of the pegmatites, and are considered to demonstrate increasing water and alkali carbonate concentrations in the pegmatite-forming liquid, and an accompanying tendency for sol/gel formation. This discovery may have important implications for the formation of the quartz cores of pegmatites. The possible origin of the alkali-carbonate concentrations in pegmatite-forming fluids is also briefly discussed.

Keywords

Precambrian pegmatitesnahcolite-rich inclusionssilica gel inclusionsorigin of alkali carbonate meltsquartz core formation
Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 7 , December 2012 , pp. 2785 - 2801
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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