Genetic Analysis of Sulfides Intergrowths in the Dajing Tin and Copper Polymetallic Deposit

The Dajing polymetallic deposit,which comprises cassiterite and a variety of sulfide ores,is a well-known multi-metal deposit.Chalcopyrite,sphalerite and pyrrhotite intergrow with each other regularly,e.g.the pyrrhotite and the chalcopyrite intergrow in the sphalerite,and the sphalerite intergrows in the chalcopyrite.The petrological observations indicated that the chalcopyrite formed later than the sphalerite and the galena did.On the basis of microscopy studies and energy spectra analyses,the authors believed that the sulfides intergrowth is genetically resulted from both exsolution and metasomatism.Pyrrhotite was separated from the earlier Fe-rich sphalerite under the influence of the late copper-rich fluid.On the sphalerite boundary,the new fluid metasomatized sphalerite and the chalcopyrite intergrowed in the sphalerite.Meanwhile,zinc was activated and supersaturated in some superposed parts to form the snow-like and star-like sphalerite interqrouths in the favorable positions of the chalcopyrite boundary.This study provided both good theoretical and good empirical evidences in uncovering the sulfides intergrowth formation mechanism,which is significant in identifying the mineral sequence and in revealing the process of mineralization.