A total of 40 samples from carbonates and 8 samples from silicate rocks were analyzed from the Sangan iron skarn deposit to examine behavior of the oxygen and carbon isotopes. The higher values of ?18O are from metamorphic calcite and dolomite and lower ones are from granitic rocks. Although the ?18O and ?13C values of calcite and dolomite in marble yield the highest values in the Sangan deposit, they are still lower than those of normal marine limestone and dolomite, i.e., reflecting coupled decarbonation and infiltrative metasomatic effects. The ?18O and ?13C values of calcite from the Sangan deposit show a progressive, gradual depletion from least-altered marbles into proximal skarn. The gradual decrease of the ?18O and ?13C values from metamorphic calcite to skarn calcite and dolomite can be ascribed to interaction of hydrothermal fluids with carbonate rocks in the area with an increase of water to rock ratio. The isotopic mass-balance calculations suggest the presence of magmatic water in the Sangan deposit.