In porphyry ore deposit models, the propylitic facies is widely interpreted to be caused by convective 16circulation ofmeteoric waters. However, recent field-­‐based and geochemical data suggest that magmatic-­‐derived fluids are likely to contribute to development of the propylitic assemblage. In order to test this hypothesis, we etermined the oxygenand hydrogen isotope compositions of propylitic mineral separates 19(epidote, chlorite and quartz), selected potassic mineral separates (quartz and magnetite) and quartz-­‐hosted fluid inclusionsfrom around the E48 and E26 deposits in the Northparkes porphyry Cu-­‐Au district, NSW,Australia. In addition, the strontiumisotope composition of epidote was determined to test for the potential contribution of seawater in the Northparkes system given the postulated island arc setting and submarine character of some country rocks.