Abstract
Experiments on metasomatism in a system comprising huebnerite and aqueous CaCl2 solution were performed at 130, 150, and 170 °C. SEM observations revealed the formation of euhedral crystals of scheelite replacing huebnerite in all experiments. The replacement texture of huebnerite by scheelite was classified as rim replacement texture. Although the molar volume ratio of replacing mineral to replaced mineral was 1.12 for the present study, huebnerite was replaced by scheelite. This suggests that the influence of molar volume ratio is small on the metasomatism of huebnerite to scheelite, which has not been expected in previous studies. Our results also suggest that the metasomatism of huebnerite to scheelite can be achieved if the CaCl2 concentration in the solution and the reaction temperature are sufficiently high. The apparent rate constant k for huebnerite dissolution in the metasomatism is approximately 10-9-10-6 mol l-1 s-1; the activation energies are 9.6, 20.7, and 31.2 kJ/mol for CaCl2 concentrations of 0.01, 0.10, and 1.00 mol/l, respectively. The precipitation of scheelite can be the rate-determining process of the metasomatism during the initial stage when the W concentration in the solution is high.
