The low-grade metamorphic minerals prehnite, pumpellyite, epidote and actinolite in rocks of basic and intermediate composition have a broad, systematic distribution in the Hamersley Basin. Assemblages of these minerals are wisespread in the Fortescue Group, the lowermost group in the Hamersley Basin. Because of sunsuitability of rock type no relevant mineral assemblages were observed in samples from the Hamersley Group. However, metamorphism of this group can be implied from mineral assemblages in the younger Turee Creek Group, and because the Hamersley Group conformably overlies the metamorphosed Fortescue Group.