The Ilkwang Cu-W deposit, located in the southeastern Kyongsang Basin, exhibits unique breccia pipe-type associated spatially with granodiorite to quartz monzonite. The oxygen, hydrogen, sulfur, and carbon isotope systematics of quartz, sulfides and calcite from the deposit are used to speculate on the origin and the processes leading to Cu-W deposition. Magmatic fluids exsolved from the granites had composition in the range δD=-45 to -49‰, (SMOW) and

=10.1 to 12.5‰ (SMOW). Arsenopyrite, chalcopyrite, and pyrrhotite of the mineralized vein have

values of -0.3 to 0.9‰ (CDT). The oxygen fugacity (

) and pH were estimated in the range -log,

=30∼31, pH=6.4∼7.3 during the deposition of sulfide minerals. Calcite representing the latest mineralization of the Ilkwang Cu-W deposit have

and

values of -4.0 to -5.0‰(PDB) and -21.2 to -15.8‰ (PDB), respectively. The fluid which deposited calcite is inferred to have had

and

values of 16.2 to 22.7‰ (SMOW) and -3.8 to -0.8‰ (PDB), respectively. The values of

suggests that they were enriched in the hydrothermal fluid as it evolved. The pH appears to be changed to less alkaline (pH=5.0∼7.0) and the oxygen fugacity were probably higher during the deposition of calcite. Although the oxygen fugacity and the pH were changed as the fluid evolved, the fluctuation was not significant probably due to the buffer solution with wall rock silicate assemblages. The ore fluid had chemical and isotopic compositions consistent with deep-seated metamorphic or magmatic fluids. These data highlight hypogene fluids exsolved from the crystallizing magma played an important role for the Ilkwang Cu-W mineralization.