The area is characterized by several intrusions into Upper Triassic to Middle Jurassic Hazelton Group fragmentals which have been biotite hornfelsed. The largest intrusive body is the Upper Cretaceous Whiting hornblende-biotite granodiorite stock.

The Sweeney Zone occurs in hornfels around a small plug of granodiorite on the south side of the Whiting stock. Mineralization consists of disseminated pyrite and veinlets of pyrite or quartz-epidote-pyrite-chalcopyrite. Minor disseminated chalcopyrite and molybdenite also occur within the granodiorite plug.