Behavior of metal iron in silicate melts at atmospheric pressure

Melting and crystallization of basaltic and peridotite systems with various admixtures of metal and oxide iron at temperatures of 1150 to 1400 degreesC at atmospheric pressure is studied. The oxidation regime was controlled by the material of the container, the initial sample mixture, and the additional solid-state buffer obstructing the free air access to the sample. The metal iron behavior substantially depends on the bulk composition of the system, oxygen fugacity, and temperature conditions. The study showed that metal iron can be released from Fe-bearing silicate systems at temperatures below their liquidus. A silicate melt primarily dissolves iron in the oxide form; under the IW buffer conditions, metal iron is reduced and oversaturates the melt with its subsequent layering and segregation of spherical particles of metal iron. The Fe concentration in the melt rises with an increase in the oxygen fugacity pO(2). Higher concentrations of Ti oxide in the system enhance the Fe solubility in the melt. In a first approximation, the Ni partition between the metal and silicate phases is consistent with the known partition coefficient. On the other hand, the Ni concentration in metal iron is controlled by the bulk composition of the system (Ni concentration in the system) and oxygen fugacity.