Abstract: Sandaowanzi gold deposit in Heilongjiang Province, located in the southeast of Yanshanian Daxinganling metallogenic belt, is a typical quartz vein deposit. Based on the study of geochemical characteristics of the ore-bearing quartz vein, surrounding rocks and corresponding volcanic rocks, the authors discuss the geological background for the mineralization. Evidences show that the ore-forming rock of the Sandaowanzi gold deposit is geochemically similar to adakite, or referred to as "C-type adakite". It is suggested that the mineralized fluid and the parent rock be both derived from the basaltic magma of the upper mantle, when the basalt intruded upward into the thickened formation of the lower crust (>50 km) following the deep faults, causing partly melting of the mafic rocks and forming of the gold deposit. Epithermal mineralization seems not the only interpretation for the genesis of the Sandaowanzi gold deposit.