Abstract:

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(Pb_4.77Cu_0.05Fe_0.04Zn_0.06)_4.92Sb_3.91S_11.00，and its simplified formula isPb₅Sb₄S₁₁.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 f_S2 and reduced fluid conditions in the ore-forming process.

Key words: Bianjiadayuan, Pb-Zn-Ag polymetallic deposit, mineral composition, falkmanite, occurrence of silver, Inner Mongolia