EGU22-7751, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Solubility of niobium in peralkaline silica-undersaturated melts at 750–850 °C, 100–200 MPa

Anna Nikolenko1,2, Christian Schmidt1, and Ilya Veksler1
Anna Nikolenko et al.
  • 1GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany (
  • 2Institute of Geosciences, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany

Solubility and complexation data are necessary for understanding conditions for the formation of magmatic and hydrothermal ore deposits. The magmatic HFSE deposits imply high solubility of these elements in alkaline silicate melts, with the most important parameters being alkalinity, halogen and water contents, temperature of the magma, and silica activity. We have conducted a series of experiments on the solubility of Nb in alkaline silica-undersaturated melts. Experiments were carried out with using two synthetic silicate glasses with different Na/Al values: NAS4 (Na2O 26.0 %(m/m), Al2O3 12.5 %(m/m), SiO2 61.5 %(m/m)) with molar Na/Al = 3.36, and NAS2 (Na2O 20.9 %(m/m), Al2O3 17.8 % (m/m), SiO2 61.3 %(m/m)) with  Na/Al = 1.93.  The glasses were prepared from finely ground mixtures of quartz, aluminium oxide, and sodium carbonate. The mixtures were heated in a Pt crucible at 900 °C and subsequently at 1100 °C, and then crushed and remelted three times. Various amounts of Nb2O5 + glass (NAS4/NAS2) were placed in 1 cm long and 3mm wide Pt capsules and arc-welded shut. Then the capsules were placed in a cold-seal autoclave and run at 200 MPa and 750 °C for about 2 weeks. Rapid quench pressure vessels were used for experiments at 850 °C, 100 MPa, and run durations of 48 – 72 hours. In some runs, distilled water and/or CaF2, NaCl were added to the reactant mixtures. Experimental products were analyzed by EMPA.

Liquids in all experiments quenched to transparent glass with small (5-10 μm) euhedral crystals of NaNbO3 composition. These NaNbO3 crystals are the only solid phase at the liquidus. In low-temperature experiments (750 °C) using the highly peralkaline glass NAS4, the Nb solubility increases substantially with addition of water from 2.54 %(m/m) Nb2O5 at dry conditions up to 2.91 %(m/m) Nb2O5 at 5 %(m/m) H2O. The Nb solubility at dry conditions at 850 °C is higher in NAS4 in comparison with less alkaline NAS2 melt (3.72 %(m/m) Nb2O5 and 2.04 %(m/m) Nb2O5, respectively). Our data at 850 °C show that the solubility of Nb in the liquid increases significantly with the addition of water and NaCl for NAS4 (4.16 %(m/m) Nb2O5 and 4.35 %(m/m) Nb2O5, respectively) and for NAS2 (2.77 %(m/m) Nb2O5 and 2.17 %(m/m) Nb2O5). The effect of CaF2 addition on the Nb solubility was insignificant.

In conclusion, the Nb solubility in silica-undersaturated melts is already high at 750 °C, and increases substantially with temperature. It also increases strongly with Na/Al ratio in the melt, with the addition of water and NaCl, but not in the presence of CaF2. This suggests that chlorine, unlike fluorine, is a ligand strongly enhancing Nb solubility in alkaline silicate melts.

This work was supported by the Deutsche Forschungsgemeinschaft via SPP2238 grants SCHM2415/7-1 and VE 619/7-1.



How to cite: Nikolenko, A., Schmidt, C., and Veksler, I.: Solubility of niobium in peralkaline silica-undersaturated melts at 750–850 °C, 100–200 MPa, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7751,, 2022.