Fornation of Inclusion with Silicagel in Topaz Crystal from Volyn Chamber Pegmatites to Thermobarometry, IR Spectroscopy

UDC 549.614 : 548.75 + 553.21 (477)

D.K. Voznyak, V.M. Khomenko

M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine

34, Acad. Palladina Pr., Kyiv-142, Ukraine, 03680


Fornation of Inclusion with Silicagel in Topaz Crystal from Volyn Chamber Pegmatites to Thermobarometry, IR Spectroscopy

Language: Ukrainian

Mineralogical journal 2015, 37 (2): 13-22

Abstract: This paper describes the results of a comprehensive study of early secondary fluid inclusions of unusual origin, first identified in the topaz crystal from Volyn chamber pegmatites. They are presented by the syngenetic liquid-gas (aqueous solution ~40 %) inclusions, and inclusions that contain silicagel. The first inclusions are homogenized at 407—410 °С in the gas phase, its density is close to critical. Eutectic temperature of the aqueous solution is –21.1 °С, the melting temperature (Tm) –3.4 °С, corresponding to a concentration of 5.5 wt. % NaCl. According to the infrared (IR) spectroscopy, liquid phase of the inclusion contains water with dissolved СО2, whereas gas phase is represented by pure СО2. The inclusion with silicagel consists of a solid phase (~70 %) and a cavity filled with gas at a low pressure. A solid phase is characterized by radial structure and was identified as an opal (silicagel). It is composed by spherulites with size of 5—6 mc in diameter. In reflected light solid phase has a weak milky-white color, it is optically isotropic and indifferent to ultraviolet rays. During heating at 370 °С the liquid appears, it is represented by almost clean water. This liquid homogenizes in a critical phase at 376 °C (Tm of ice is –0.2 °С). At lower temperatures (~370 °C) water is adsorbed by silicagel solid phase. IR spectra of the solid phase are identical to spectra of natural opals. The results obtained lead to the following conclusions: 1. The silicagel in the inclusion is associated with a high temperature (~410 °C) process of emergence in pegmatites of an aqueous solution with a high SiO2 content. Most likely, widely distributed in Volyn pegmatites opals also were formed similarly, so their formation was synchronous to period of pegmatite formation in the Proterozoic time. 2. The presence of heavy fluid that was in equilibrium with the acidic aqueous solution was one of the favorable growth factors of perfect crystals of quartz and topaz as pegmatitic body that contained topaz crystal with inclusions studied belongs to the highly productive objects of deposit.

Keywords: opaz, fluid inclusions, silicagel, homogenization temperature, IR spectroscopy, Volyn chamber pegmatites.


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