The Fontaine Creek showing is underlain by rocks of the Mississ- ippian to Pennsylvanian Crooked Amphibolite Formation. These are considered to be correlative to the Slide Mountain Group. The Crooked Amphibolite is located along a major thrust fault (the Eureka Thrust) separating the Quesnellia Terrane from the Barkerville Terrane. Included within the Crooked Amphibolite are a number of ultramafic bodies, discontinuously distributed along the Eureka Thrust.

Near the junction of Reddish and Fontaine creeks is a serpentin- ized ultramafic with scattered occurrences of short fibre asbestos veinlets.