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Abstract

In this paper we show that the pegmatite-forming processes responsible for the formation of the Malkhan pegmatites started at magmatic temperatures around 720 °C. The primary melts or supercritical fluids were very water- and boron-rich (maximum values of about 10% (g/g) B2O3) and over the temperature interval from 720 to 600 °C formed a pseudobinary solvus, indicated by the coexistence of two types of primary melt inclusions (type-A and type-B) representing a pair of conjugate melts. Due to the high water and boron concentration the pegmatite-forming melts are metastable and can be characterized either as genuine melts or silicate-rich fluids. This statement is underscored by Raman spectroscopic studies. This study suggested that the gel state proposed by some authors cannot represent the main stage of the pegmatite-forming processes in the Malkhan pegmatites, and probably in all others. However there are points in the evolution of the pegmatites where the gel- or gel-like state has left traces in form of real gel inclusions in some mineral in the Malkhan pegmatite, however only in a late, fluid dominated stage.

Item Type:	Article
Authors/Creators:	Thomas, R and Davidson, P and Badinina, E
Keywords:	melt inclusion; fluid inclusion; gel inclusion; water; boron and cesium determination; pegmatite genesis
Journal or Publication Title:	Minerals
ISSN:	2075-163X
DOI / ID Number:	https://doi.org/10.3390/min2040435
Additional Information:	Copyright 2012 The Authors
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