Petrographlc and geochemical studies demonstrate that the prevailing environment during
the formation of the different Baguio Mining District (BMD) mafic-silicic plutonic rocks was
subduction-related. The source region/s responsible for the BMD intrusive complexes is/are
characterized by island arc signatures. Mixing in the mantle source region of several components (MORB, IAB, OIB, sediments, crust?) could have occurred and can explain the geochemical signatures revealed by the BMD rocks. Field evidence, specifically the exposed sedimentary package of the two districts, supports the geochemical- and petrological-based model that the region evolved from a marginal basin to a mature island arc setting.