The area is underlain by rocks of the Ordovician to Triassic Apex Mountain Complex. They are represented by a highly deformed package of cherts, argillites, tuffaceous siltstones, greenstones and minor limestones that were originally subdivided into the Independence, Bradshaw, Old Tom and Shoemaker formations.

The Apex Mountain Complex rocks are intruded by granodiorite and granite of the Middle Jurassic Cahill Creek pluton. Locally, the rocks are comprised mainly of cherty argillite and andesitic ash tuff, which are intruded by granodiorite dykes. A siliceous sample of chert and quartz, taken close to one of these dykes, analysed 2.06 grams per tonne gold, 13.8 grams per tonne silver, greater than 1 per cent copper and greater than 1 per cent arsenic (Assessment Report 14522, page 7, sample 3761E).