Sedimentary rocks of the Aldridge Formations underlie the area. The sediments are Proterozoic in age and consist of quartzwackes, quartz arenites, and siltstones. Diorite of the Proterozoic Moyie Intrusion occurs as dikes and sills.

A drill hole on the Vulcan 5 intersected fine-grained wackes to quartz wackes of the Aldridge Formation with gabbro sills. Bedding varies from finely laminated argillaceous rocks to medium bedded, more quartzitic units. Metamorphism is greenschist level with local development of intense biotite and or silicification. There are very minor occurrences of graphite along fractures and as narrow 'bedded' seams. The sulphides, most commonly pyrrhotite and pyrite, occur sporadically as fine laminations or as cross-cutting veins and fracture fillings. Minor associated sphalerite and galena were noted locally.