The region in which the Jen-Beaver showing occurs is within the Intermontane Belt, underlain dominantly by Lower to Middle Jurassic volcanic and sedimentary rocks of the Hazelton Group. These as- semblages are overlain by the Upper Cretaceous to Lower Tertiary Ootsa Lake Group and Miocene plateau basalt. Intruding Lower Jurassic rocks of the Hazelton Group in the northeastern part of the map sheet is a belt of granodiorite, diorite and quartz diorite plutons of the Lower Jurassic Topley intrusive suite. Felsic plutons of probable Cretaceous age intrude both Lower and Middle Jurassic Hazelton strata.

The property area is underlain by felsic rocks of the Topley Intrusive Suite, mainly quartz monzonite which varies from nonporphyritic to porphyritic with phenocrysts of quartz and feldspar. Intruding the quartz monzonite is a granitic phase known as the Casey Granite which varies in composition from quartz monzonite to alaskite. Fractures cutting the Casey granite strike at 65 degrees and dip 85 degrees north, and some host quartz veinlets up to 1.0 centimetres wide with specular hematite, magnetite and rare molybdenite. The wallrock has undergone weak argillic and potassic alteration.