EXPERIMENTAL STUDY OF THE SYSTEM H3BO3–NAF–SIO2-H2O AT 350–800 °C AND 1–2 kbar BY THE METHOD OF SYNTHETIC FLUID INCLUSIONS
I.S. Peretyazhkoa, S.Z. Smirnovb, A.R. Kotel’nikovc, and Z.A. Kotel’nikovad
a A.P. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1a ul. Favorskogo, Irkutsk, 664033, Russia
b V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
c Institute of Experimental Mineralogy, Russian Academy of Sciences, Chernogolovka, 132432, Russia
d Institute of Geology of Ore Deposits, Petrography, Mineralogy and Geochemistry, Russian Academy of Sciences, 35 Staromonetnyi per., Moscow, 119017, Russia
Keywords: H3BO3, NaF, fluid inclusions, P–Q type solution
Pages: 349-368
Abstract
The phase state of fluid in the system H3BO3–NaF–SiO2-H2O was studied at 350–800 °C and 1–2 kbar by the method of synthetic fluid inclusions. The increase in the solubility of quartz and the high reciprocal solubility of H3BO3 and NaF in water fluid at high temperatures are due to the formation of complexes containing B, F, Si, and Na. At 800 °C and 2 kbar, both liquid and gas immiscible phases (viscous silicate-water-salt liquid and three water fluids with different contents of B and F) are dispersed within each other. The Raman spectra of aqueous solutions and viscous liquid show not only a peak of [B(OH)3]0 but also peaks of complexes [B(OH)4]–, polyborates [B4O5 (OH)4]2-, [B3O3 (OH)4]–, and [B5O6 (OH)4]–, and/or fluorborates [B3F6O3]3-, [BF2 (OH)2]–, [BF3 (OH)]–, and [BF4]–. The high viscosity of nonfreezing liquid is due to the polymerization of complexes of polyborates and fluorine-substituted polyborates containing Si and Na. Solutions in fluid inclusions belong to P–Q type complicated by a metastable or stable immiscibility region. Metastable fluid equilibria transform into stable ones owing to the formation of new complexes at 800 °C and 2 kbar as a result of the interaction of quartz with B-F-containing fluid.
At high concentrations of F and B in natural fluids, complexes containing B, F, Si, and alkaline metals and silicate-water-salt dispersed phases might be produced and concentrate many elements, including ore-forming ones. Their transformation into vitreous masses or viscous liquids (gels, jellies) during cooling and the subsequent crystallization at low temperatures (300–400 °C) should lead to the release of fluid enriched in these elements.
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