Experimental studies on ion exchange equilibria between minerals and aqueous chloride solution in the system CaWO₄-FeWO₄-MnWO₄ under supercritical condition

Ion exchange experiments in the system CaWO₄-FeWO₄-MnWO₄-(Ca, Fe²⁺, Mn²⁺)Cl₂-H₂O, corresponding to scheelite-ferberite-huebnerite series mineral as solid phase, were carried out at 400 and 600°C under 1000 kg/cm². Ferberite and huebnerite form a continuous solid solution (wolframite ss), which may exhibit thermodynamically ideal behavior. Also, ferrous ion tends to concentrate preferably into wolframite ss than into aqueous chloride solution. This tendency becomes more pronounced with decreasing temperature. Scheelite and wolframite ss do not dissolve into each other essentially, but form a wide miscibility gap. The Ca/(Ca+Fe²⁺+Mn²⁺) mole ratios of aqueous chloride solution coexisting with both minerals are about 0.65 at 400°C and 0.3 at 600°C. Temperature has a significant effect on the mole ratio, although a slight variation due to the compositional change of wolframite ss is recognized. The present experimental results cast a doubt on “wolframite geothermometer”.