The Metallogenic Mechanism Of Dongshengmiao Ore Deposit,Inner Mongolia

Dongshengmiao deposit is the largest zinc polymetallic deposit in Langshan metallogenic belt.This paper is aimed at constraining the metallogenic mechanism of Dongshengmiao Deposit by integrated geological and geochemical(elemental and isotopic)investigation of the main ore-bearing sequences.Black rock series is the most important host rock type.Compared with pyrite in massive rich sulphide ores,the irregular lumps pyrite in this black rock series have higher ?57Fe values and have an overall lowed sulfur isotopic compositons,we speculate that the irregular pyrite is the product of diagenetic transformation.And there is no significant relationship with hydrothermalism.Therefore,we believe that the precipitated environment of Dongshengmiao deposit was relatively oxidized and stored under the diagenetic conditions of absulte reduction.Both vein pyrrhotite and massive sulphide ores have lower ?57Fe values,but the former is heavier on the whole than the latter.So we believe that the pyrrhotite in the black rock series is the product of the later hydrothermal filling and metasomatism in the earlier rock and ores.In the lenticular part of the main orebody,the most distinctive pattern revealed by Zn,Fe isotopes data is the lateral systematic trend of increasing 866Zn and ?57Fe values from west to east.The lateral isotopic variation,indicates that Rayleigh fractionation is the dominant factor controlling the observed isotopic variation of sphalerite.As we expected,the spatial distribution of isotopes indicates the centre of upwelling ore-forming fluids is located at the west of deposit where breccia mineralization is common.Therefore,we suggest that more attention should been paid to the area for deeper ores when the next exploration is taken.Through combination of geological and geochemical characteristics,and Fe,Zn isotope geochemistry,we proposed that epigenetic replacement rather than syngenetic ore-forming is the main mineralization in zinc orebody.