The Yongxin gold deposit located in the southern part of the Nenjiang-Heihe tectonic mélange zone is a newly discovered altered rock type gold deposit controlled by tectonic belt. The gold-silver minerals and auriferous sulfides in this deposit were systematically studied by optical microscope, electron microprobe analysis and back scattered electron images, and the results show that gold-silver minerals are mainly native gold, subordinate electrum, and minor amounts of intergranular gold, with the crystal size in the range of 5 to 20 μm and mainly occurring as inclusions and fissure fillings. The fineness varies from 843 to 917, 888 on average. Gold-silver minerals were found in pyrite and galena, mainly pyrite. At the early stage of mineralization, the crystalline form of coarse-grained yrite was mainly cubic and crushed by late stress. At the main ore-forming stage, the crystalline form of fine-grained pyrite was dominated by cubic and pentagonal dodecahedron. The Co-Ni-As phase diagram shows that mineralization was closely related to magmatic fluids, the Fe/(S+As) ratio of the pyrite and the fineness indicate that this deposit was formed at the medium temperature and medium to deep mineralization environment. The Yongxin gold deposit is partially similar to and yet obviously different from decratonic (Jiaodong type) and orogenic gold deposits.