The Fairchild Lake map area is underlain by two principal sedimentary successions, Middle Proterozoic Wernecke Supergroup and unconformably overlying Middle to Late Proterozoic Pinguicula Group. The angular unconformity between the successions was caused by an intervening period of deformation known as Racklan orogeny. A third succession, herein named the Slab volcanics, is inferred to have been deposited after Racklan orogeny and before Pinguicula Group deposition. Mineralization occurs as sedimentary exhalative, vein, and intrusive breccia occurrences within Wernecke Supergroup. The sedimentary exhalatives contain Zn, Pb, Cu and Ag in shaley horizons within a mainly dolomitic sequence. The vein occurrences contain Zn, Pb, Cu, Ag, Au and U. The intrusive breccias, collectively known as Wernecke breccia, host Cu, Co, U, Ag and Au. Wernecke breccia was probably generated by explosive expansion of volatile-rich fluids. Brecciation was preceded by Racklan orogeny and intrusion of igenous dykes. The dykes and the breccia-related mineralizing fluids may have a common source in postulated underlying magma chambers. Local supergene enrichment of breccia mineralization was caused by Middle to Late Proterozoic weathering before deposition of Pinguicula Group.
