Phase Equilibria of Several Tungsten Deposits in Southern China

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This paper reviews the features of several tungsten ore deposits in southern China,inclu-cling the Shizhuyuan,Yaogangxian,Xihuashan,Dangping,Piaotang and Dajishan mines.The authots think that the formation depth of the greisen-type deposits is intermediate be-tween the pegmatite-and porphyry-type deposits.Using phase diagrams of the model system K_2O-A1_2O_3-SiO_2-H_2O-HF,the formation mechanism of greisens has been argued.The variationof mineral assemblages from K-feldspar,muscovite to topaz reflects a gradual increase in acidity.This variation can be used as a criterion to appreciate the depth of mineralization.Phase equilibria of tungsten minerals in grcisen and skarn deposits can be depicted on che-mical potential diagrams of the model system CaO-FeO-WO_3-CO_2-F_2O_(-1).The assemblage wol-framite+fluorite is shown to have ben transformed to scheelite+magnetite with decreasingμHF.Depending on CO_2 activity in the fluids,there are two distinct phase diagrams.One shawsthat wolframite is incompatible with calcite,and the other demonstrates that scheelite is in-compatible with rhodochrosite.On the phase diagrams of the model system FeO-MnO-WO_3-F_2S_(-1),huebnerite is transformed to ferberite with increasing μF_2O(-1)or μF_2S~(-1).During the replacement of wolframite by scheelite,the wolfrarnite residue must have beenenriched in Mn. This paper reviews the features of several tungsten ore deposits in southern China, inclu-cling the Shizhuyuan, Yaogangxian, Xihuashan, Dangping, Piaotang and Dajishan mines. The authots think that the formation depth of the greisen-type deposits is intermediate be-tween the the formation mechanism of greisens has been argued. The variation of mineral assemblages from K-feldspar, muscovite to topaz reflects a gradual increase in acidity. This variation can be used as a criterion to appreciate the depth of mineralization. Phase equilibria of tungsten minerals in grcisen and skarn deposits can be depicted on che-mical potential diagrams of the model system CaO-FeO-WO 3 -CO 2 -F 2 O (-1). The assemblage wol-framite + fluorite is shown to have ben transformed to scheelite + magnetite with decreasing μHF. Depending on CO_2 activity in the fluids, there are two distinct phase diagrams. One shawsthat wolframite is incompatible with calcite, and the other demonstrates that scheelite is in compatible with rhodochrosite. On the phase diagrams of the model system FeO-MnO-WO_3-F_2S _ (- 1), huebnerite is transformed to ferberite with increasing μF_2O (-1) or μF_2S ~ (-1) .uring the replacement of wolframite by scheelite, the wolfrarnite residue must have beenenriched in Mn.
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