Mineral Composition of Bianjiadayuan Pb-Zn-Ag Polymetallic Deposit in Inner Mongolia and Its Origin Significance

Located in the southern Daxing'anling metallogenic belt,Bianjiadayuan Pb-Zn-Ag deposit is a new discovery in recent years of higher ore grade lead-zinc-silver polymetallic deposit. Detailed microscopic identification and electron analysis show that metalliferous minerals of this deposit mainly consist of galena,sphalerite, pyrite,chalcopyrite,pyrrhotite, arsenopyrite and stannine. Silver minerals mainly consist of tetrahedrite, freibergite and pyrrhotite. In addition,we also found a large number of falkmanites in the mine,which are intimately accompanied by galena,chalcopyrite and tetrahedrite. Falkmanite crystals show as needle,pillar, bunchiness and anhedral grain forms,and their grain sizes commonly vary from 5 to 150 μm. Electron microprobe analysis also shows that its corresponding formula is( Pb4. 77Cu0. 05Fe0. 04Zn0. 06)4. 92Sb3. 91S11. 00,and its sim-plified formula is Pb5Sb4S11. Falkmanite is generally the product of the late mineralization with a low tempreture. The formation of falkmanite may be favored by a low temperature,increasing fS2and reduced fluid conditions in the ore-forming process.