The Sima occurrence is located on the north side of the Conuma River, approximately 24 kilometres northwest of the community of Gold River.

The area is underlain by diorite and granite of the Jurassic Island Plutonic Suite. These plutonic rocks intrude volcanics and sediments of the Upper Triassic Vancouver Group, Karmutsen Formation and the Pennsylvanian to Permian Sicker Group (Geological Survey of Canada Map 1537A).

Locally, Buttle Lake limestone occurs in contact with Karmutsen basalts. Within the basalts, there are several dikes or bedded lenses of solid magnetite. Some of the magnetite dikes are sulphide free; others are copper and iron sulphide rich.

In 1993, a program of geological mapping and sampling was completed. A sample of magnetite returned 77.09 per cent Fe2O3 and 13.43 per cent FeO (Assessment Report 23378).