Major and trace element data for plagioclase and whole-rocks from Japan sampled and filtered from the GEOROC online database (http://georoc.mpch-mainz.gwdg.de/georoc, state: 1 January 2017). The data was used to test the recently developed plagioclase porphyry indictor mineral, as described in Williamson et al. (2016, Nature Geoscience, 9: 237-241), on samples from Japan. Japan is considered a negative control as it has no known porphyry deposits, despite showing favourable geology. The data was used in Williamson B.J., Hodgkinson M., Imai A., Takahashi R., Armstrong R.N., Herrington, R.J., 2018. Testing the Plagioclase Discriminator on the GEOROC Database to Identify Porphyry-Fertile Magmatic Systems in Japan, Resource Geology, 68: 138-143.