(Phase equilibria of several tungsten deposits in southern China.)

The features of several W ore deposits in southern China are reviewed, including the Shezhuyuan, Yaogangxian, Xihuashan, Danping, Piatang and Dajishan mines. It is proposed that the formation depth of greisen-type deposits is intermediate between the depths of pegmatite- and porphyry-type deposits. Using phase diagrams of the model system K₂O-Al₂O₃-SiO₂-H₂O-HF, the formation mechanism of greisens is argued. The variation of mineral assemblages from K-feldspar to muscovite and topaz reflects a gradual increase in acidity. This variation can be used as a criterion to appreciate the depth of mineralization. Equilibria of W minerals in greisen and skarn deposits can be shown on chemical potential diagrams of the model system CaO-FeO-WO₃-CO₂-F₂O_-1. The assemblage wolframite + fluorite is shown to have been transformed to scheelite + magnetite with decreasing mu _Hf. Depending on CO₂ activity in the fluids, there are two distinct phase diagrams, one showing that wolframite is incompatible with calcite, and the other that scheelite is incompatible with rhodochrosite. On the phase diagrams of the model system FeO-MnO-WO₃-F₂S_-1 hubnerite is transformed to ferberite with increasing mu /F₂O_-1 or mu /F₂S_-1. During the replacement of wolframite by scheelite, the wolframite residue must have been enriched in Mn.-P.Br.