Water- and Boron-Rich Melt Inclusions in Quartz from the Malkhan Pegmatite, Transbaikalia, Russia

Abstract

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) B 2 O 3 ) 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.

Inclusions of Amorphous and Crystalline SiO2 in Minerals from Itrongay (Madagascar) and Other Evidence for the Natural Occurrence of Hydrosilicate Fluids

“…This resonates with the suggestion of another group of researchers that a vitreous phase in a rehomogenised type-B melt inclusion from elsewhere is a gel rather than a glass, because a mica crystal grew within it over a week spent at room temperature [21]. However, the latter group classified quartz-hosted inclusions from the Malkhan pegmatites that are akin to the aforementioned ones as peralkaline to peraluminous type-A melt inclusions (those in Figure 3a-c) [62]. These authors also reported quartz-hosted peralkaline type-B and type-C melt inclusions from the same locality, which consist of a large sassolite crystal, sometimes a few small silicate crystals, and a fluid with a vapour bubble (Figure 3d,e) [62].…”

Extreme Enrichment of Cs during the Crystallization of the Ehrenfriedersdorf Pegmatite Melt Related to the Variscan Tin Mineralization

“…Figure 4d displays the extreme Cs enrichment near the solvus crest of the Melt-H 2 O -B 2 O 3 system as Cs-pentaborate (Ramanite-(Cs). At first, this Cs-pentaborate was found in pegmatite material from the Isle of Elba (see [21] -later also in Malkhan (Thomas et al, 2012) [22] and Ehrenfriedersdorf (Sauberg mine). The Lorentzian distribution of Cs vs. B is untypical, and Cs vs. H 2 O is typical for some elements (Be, Sn, and others [5,6].…”

Mineralogical and chemical characteristics of a powder and purified quartz from Yunnan Province

“…However, the concentrations of B and Ti (Table 2) were much higher than typical for quartz deposits of different origins [19]. The major, minor, and trace element contents, respectively, suggested that the powder quartz mine was associated with geological environment and mineralization of felsic rocks of pegmatitic origin as indicated by the higher B and Ti contents [20].…”