From the oldest to youngest, Karmutsen andesite/basalt, Quatsino limestone, Parson Bay pyritic shale and massive limestone, and Bonanze tuffs, chert and volcanic breccia are intruded by hornblende porphyry and granodiorite of the Island intrusions. Pyrite and minor amounts of chalcopyrite and molybdenite are scattered mainly in fractures. Alteration is widespread, ranges from weak to intense, and varies both in type and intensity over very short distances.