| 3 | Mineral Association and Mineralogical Criteria for the Formation Conditions of A B-F-Sn-Bi Skarn in Damoshan,Gejiu Tin Field,Southwest China显示文摘The Damoshan deposit is a small B-F-Sn Bi exoskarn deposit and contains a distinctive mineral assemblage comprising andradite,vesuvianite,calcite,diopside,magnetite,hematite,nordenskioldine,cassiterite,varlamoffite,schenfliesite,native bismuth,eulytite,bismite and bismuthite,in which the occurrence of eulytite is the first reported in China.Textures of the mineral paragenses show that andradite,vesuvianite and diopside were the earliest phases formed during metasomatism,i.e.,the skarn forming stage.Then nordenskioldine,magnetite and native bismuth,perhaps together with eulytite,were precipitated at the stage of retrograde alteration.The minerals varlamoffite,schoenfliesite,hematite ,bismite and bismuthite were probably the product of supergene alteration.The minerals were analyzed by means of electron microprobe.The data on the ,coexisting phases and their compositons show that during the metasomatism reduced F-and Sn-rich primary mineralizing solutions reacted with highly oxidized carbonated of the Gejie Formation,producing a high Fe^2+/Fe^3+ skarn(vesuvianite-fluorite skarn)near the contact of granite,and a low Fe^2+/Fe^3+ skarn(vesuvianite-fluorite skarn)near the contact of granite,and a low Fe^2+/Fe^3+ skarn(andradite skarn)in the outer zone of the skarn body in which andradite is extremely tin-bearing up to 5.14 wt% SnO2),In the retrograde alteration stage ,B-rich,but F-and Si-deficient mineralizing solutions replaced the tin-bearing andradite,forming an association of nordenskioldine and magnetite,No sulphides were deposited at this stage because of the oxidization ambient conditions in the andradite skarn.In the spergene oxidation zone,the nordenskioldine was dissolved into varlmoffite and calcite,the native bismuth was transformed into bismite or bismuthite ,and the magnetite was altered into hematite under the action of the CO2-rich supergene solutions. | 陈骏 C.HALLS C.J.STANLEY | 1992 | Chinese Journal Of Geochemistry1992，11，2： | 3 |
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