Because of the reports of six separate sources of radioactivity, all within a distance of 2½ miles of the town of Port Lincoln, further geologic investigations were undertaken, prior to the appraisal of the area as a possible source of uranium. The geology of the area comprising these six occurrences was mapped at scale of 4 inches equal to 1 mile, to determine the geologic relationships between these occurrences. The map area is made up of a complex highland belt of Archean crystalline metasediments, intruded by highly sodic or granitic solutions or gases of magmatic origin, under deep-seated conditions of temperature and pressure. The resulting rocks how the effects of differential sodic metasomatism, and range in composition from highly sodic augen gneisses, through sodic hornblende granites and gneisses, to relatively unaffected amphibolitic country rock. Structurally, all rock types are gneissic or schistose, strike roughly north, and dip steeply to the west. All appreciable uranium mineralisation is restricted to a relatively narrow zone of granitized metasediments, which can be traced intermittently in a north-south direction through the middle of the area and which are strongly fractured and deformed. Host rocks and mode occurrence of uranium mineralisation are remarkably similar, uraninite occurring as minute grains thinly disseminated throughout a granulated quartz-feldspar groundmass in the foliated sodic hornblende granite. These granulated areas provided channelways for uraniferous ore solutions and were apparently the main ore control. The six uranium prospects are identified as follows: Gibson Prospect No. 1 (Hospital), Gibson Prospect No. 2 (Hargistrom) Gibson Prospect No. 3 (Ainslee North and South), Lomax Prospect, Frazer Prospect, and Davey-Wollaston Prospect. Gibson Prospect No. 1 was previously tested by diamond drilling. Further subsurface exploration at the other prospects would apparently involve the possibility for additional low-grade reserves (2-3 lbs. U308/ton) of highly theoretical tonnages. Small initial programmes, comprising about 350 feet of diamond drilling and possibly auger drilling, are considered feasible and practicable at the Lomax and Ainslee South Prospects.