The Composition of a Silicate Melt of Fluorite-Containing Ongonites at 700–800°C, 100 MPa, and Different Oxygen Fugacities

AbstractExperiments on the melting of samples of fluorite-containing ongonites from the Ary-Bulak massif at 700–800°C at a pressure of 100 MPa and oxygen fugacity corresponding to the Ni–NiO and Mt–Hem buffers were carried out. In all experiments, the limit of the fluorine content in the aluminosilicate melt and saturation with respect to fluorite and topaz were reached. The change in oxygen fugacity did not qualitatively affect the phase relations in the studied samples but led to a slight increase in the solubility of topaz and a decrease in the solubility of fluorite in the silicate melt. In the composition of the silicate melt, a corresponding change occurred in the value of the agpaite coefficient Ka and the content of CaO.