A basic to ultrabasic suite of diorites to peridotites crops out over an area of 0.7 km2, 10 km west of Tumby Bay. Country rocks are dominantly quartz-feldspar gneisses and biotite schists. Highest geochemical values are chromium 2 000 ppm, nickel 1 500 ppm, and cobalt 150 ppm, in peridotites. Copper, lead and zinc occur in amounts up to 50, 80 and 150 ppm respectively, regardless of rock type. The mineralogy is dominated by olivine, pyroxene, serpentine and plagioclase with quartz generally absent. Plagioclase is commonly bytownite or labradorite. Metallic minerals are magnetite, pentlandite, chalcopyrite and pyrite with a volume ratio of 6:2:2:1; sulphides represent <0.2 volume % of the total rock. 59% to 77% of the total nickel is within silicates, mainly olivine and serpentine. An intrusive magmetic origin appears most likely.