Schröcke, H.; Trumm, A.; Hochleitner, Rupert
The transport of tungsten and the deposition of tungsten double oxides in fluid, aqueous solutions [Über den transport von Wolfram und den Absatz von Wolfram-Doppel-Oxiden in fluiden wässrigen Lösungen].
In: Geochimica et Cosmochimica Acta, Vol. 48, No. 9: pp. 1791-1805
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The transportation of W in aqueous gas-phases at and above 500°C is examined using thermodynamic data. The transport of W is possible as fluoride and oxifluoride. The deposition of wolframite continues with decreasing temperature and pressure. The stabilities of wolframates in hydrothermal solutions are examined for temperatures up to 300°C with Eh-pH-diagrams, exchange reactions of wolframite with oxides, sulfides and dissolved ions. Fe2WO6 becomes stable against Fe2O3 + WO3 above 126°C. At 300°C its range of stability begins at high pO2 which is not realised in hydrothennal endogenous solutions. In consequence of the very low Gibbs energies of MgWO4, CaWO4 and BaWO4, the minerals MgWO4 and BaWO4 should be more important than wolframite, if Mg and Ba coexist in solution together with W. Co and Ni also should be found as trace elements in wolframite, if Co and Ni were in solution in sufficiently high concentrations together with W.