The Qingshuigou-Bailiugou ore field, located in the western part of north Qilian Mountains, is one of the important copper-polymetallic ore deposits in China. The authors studied the fluid inclusions within quartz for the representative ore deposit by using homogenization method and Laser Raman method. The results showed that the fluid includes three types of inclusions: single-phase liquid inclusion, two-phase liquid-vapor inclusion and the CO₂-bearing three phase inclusion. It is suggested that the ore-forming fluid may be derived from the mixed seawater and magmatic water.