1 The First Institute of Geological Exploration of Heilongjiang Province, Mudanjiang 157011, Heilongjiang China; 2 School of Earth and Resources, China University of Geosciences, Beijing 100083, China

The Erdaokan Ag-Pb-Zn deposit is a large Ag-Pb-Zn deposit with rich organic matter discovered for the first time in the Duobaoshan metallogenic belt, Great Xing’an Range. In order to determine the contribution of organic matter to mineralization, the authors systematically summarized the basic characteristics of deposit geology, ore minerals and wall rock alteration on the basis of previous studies, and carried out the microscopic observation and organic composition analyses of organic matter in ore and wall rocks. The results show that the ore bodies of Erdaokan Ag -Pb -Zn deposit occur in the NW??trending tectonic fracture zone and are closely associated with the carbonaceous mudstone and limestone of the Upper Silurian-Middle Devonian Niqiuhe Formation. The ore is composed of structural breccia. The ore minerals mainly consist of magnetite, pyrite and galena, followed by sphalerite, tetrahedrite, hematite and siderite, etc. , and the Ag-bearing minerals are mainly argentite and pyrargyrite. A large amount of bitumen associated with ore minerals appears in the ore. The carbonaceous mudstone and limestone of Niqiuhe Formation in the host rock are equally enriched with organic carbon content of 0. 77% and 3. 37%, respectively, which provide material guarantee for the formation of bitumen and promote the precipitation of metals in the process of mineralization. It is concluded that the thermochemical reduction of sulfate with organic matter is an important mechanism of metal precipitation in the Erdaokan Ag -Pb -Zn deposit.