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

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.