MOLYBDENUM PARTITION BETWEEN MELTS OF NATURAL AND SYNTHETIC ALURNINOSILICATES AND AQUEOUS-SALT FLUIDS

Abstract

The molybdenum partition between fluid phases of the composition H2O-NaCl (with NaCl concentrations ranging from 0 to 100%) and melts of natural and synthetic aluminosilicates was examined at a temperature of 800°C and pressures of 1.0, 1.5, and 2.0 kbar. The experiments were carried out by ampoule techniques in an externally heated high-pressure apparatus with the subsequent fast quenching of the samples and their microprobe analysis. In most of the experiments, equilibrium was approached by the preliminary introduction of the element into the system alternatively with the glass or solution. It was established than Mo occurs in the solution exclusively in the form of aqueous compounds over the whole interval of NaCl concentrations. No noticeable correlation between the Mo distribution and the SiO2 and Al2O3 concentrations in the melts were detected. The determined Mo partition coefficients (KMo = CF/CL, where CF and CL are the Mo concentration in the fluid and melt phases, respectively) at 800°C and 1.5-2.0 kbar are 0.90 ±0.2 for the granite-water system, 1.4 ± 1.1 for the granite-1m NaCl solution system, 8.9 ± 3.0 for the albite-1m NaCl solution system, and 10.9 ± 4.0 for the Ab-Qz eutectic-1m NaCl solution system. A negative correlation was established between KMo and the CaO concentration of the aluminosilicate melt.