Abstract: "The relative isotopic abundance of copper has been measured in a number of minerals. Suites of samples from Michigan and the Colorado Plateau have been examined to determine if local variations due to isotopic exchange or diffusion could be found. The relative isotopic abundance of copper in specimens from a number of other places was also determined. The variations noted were small but in most cases were felt to be significant because they were larger than the experimental error (0.1 percent in the ratio). A total spread of +3 to -8 parts per mil compared to the standard was found in the specimens tested."