College of Earth Sciences, Jilin University, Changchun 130061, China

The mineral composition and element distribution of tailings in Yangjiazhangzi molybdenum ore deposit were studied by grain-size analysis, polarizing microscope, X-ray powder diffraction, and major and trace elemental tests. The results indicate that the main component of tailings is fine sand, which is composed of SiO₂, CaO and Al₂O₃, and the minerals of quartz, plagioclase, molybdenite, pyrite, chalcopyrite, galena and sphalerite. Along the sand discharge direction, Cu, Zn, Co and Cd are enriched near the sand discharge port, Ni is enriched in the middle, Pb and Bi are enriched in the vicinity of the dam. Along the vertical sand discharge direction, Zn, Pb and Cd are enriched on the central low-lying surface. In the vertical section, Hg is concentrated in the shallow stratum, Cd is enriched in the surface of the B section, and migrating downward on other sections Cd, Pb, Zn and As are descending faster, some of them generate secondary enrichment at 40~80 cm.