STABLE oxygen isotope is not only an effective approach to tracing water-rock interactions, but also canprovide much information about ore-forming temperature and source and evolution of ore fluids in thestudy of hydrothermal deposits. The rare-earth elements (REE) can be used to trace the sources ofore-forming materials and can also, to some extent, indicate the physical and chemical properties of fluids in the geochemical processes. The combination of these two aspects of research can effectivelyprobe into the geochemical behavior and evolution of REE in the process of water-rock interaction duringhydrothermal ore deposition. On the other hand, the essence of REE as tracers in hydrothermal mineralization can be better understood. In this note the Lemachang independent Ag deposit in northeastern Yunnan is selected for a case study. STABLE oxygen isotope is not only an effective approach to tracing water-rock interactions, but also canprovide much information about ore-forming temperature and source and evolution of ore fluids in the study of hydrothermal deposits. The rare-earth elements (REE) can be used to trace the sources ofore-forming materials and can also, to some extent, indicate the physical and chemical properties of fluids in the geochemical processes. The combination of these two aspects of research can effectivelyprobe into the geochemical behavior and evolution of REE in the process On the other hand, the essence of REE as tracers in hydrothermal mineralization can be better understood. In this note the Lemachang independent Ag deposit in northeastern Yunnan is selected for a case study.