In the Sir Joseph Banks Group of southern Spencer Gulf offshore islands, outcropping Archaean arenaceous, arkosic and calcareous sedimentary rocks appear to have been folded and granitised prior to the deposition of the Adelaidean System sedimentary rocks elsewhere in South Australia. During the later stages of metasomatism, scheelite and molybdenite were introduced, accompanied by quartz and small amounts of wolframite, chalcopyrite, galena and sphalerite. The presence of fluorite, tourmaline and scapolite implies that the volatile fluids contained fluorine, boron and chlorine. During Tertiary times the granitic basement was peneplained, and later was covered by Tertiary to Recent deposits, now being eroded by wave action. Mineralisation found on Spilsby Island has been described in previous reports. A survey for exposed fluorescent minerals made with ultra-violet lamps over the other islands revealed only a few small disseminations and rare thin veins of scheelite on Reevesby, Hareby and Boucaut islands.