Oxygen isotope values of vein quartz from the Star-Morning mine range from 13.2‰ to16.2‰ relative to standard mean ocean water. Calculated isotopic values of water in equilibrium with the vein quartz at 325 °C range from 7.2‰ to 10.2‰. The δ18Oquartz values decrease with depth in the mine. The δD values of quartz inclusion fluids range from -18‰ to -105‰ and do not significantly correlate with depth. Oxygen isotope values of Belt Supergroup wholerock samples range from 13.8‰ to 16.8‰. The data indicate that the fluids were a mix of metamorphic water released from the Belt rocks during low-grade metamorphism, and 18O-shifted meteoric water.