REACTIVATED BASEMENT STRUCTURES CONTROLLED EMPLACEMENT OF TRIASSIC-JURASSIC STIKINE CU-AU PORPHYRY DEPOSITS

Late Triassic and Early Jurassic porphyry and related deposits of Stikinia (northwestern BC) focus along major fault arrays that display recurrent magmatism from ca 220 to 185 Ma - a pattern that differs markedly from the parallel, east-migrating magmatic belts of Quesnellia. North-trending, multi-episodic belts of western Stikinia host Schaft Creek (ca 220 Ma), Galore Creek (ca 212 Ma), KSM (ca 195 Ma), and epithermal, porphyry-related Brucejack (ca 192-185 Ma). Nearly orthogonal, east-west cross-structures interrupt and offset the northerly trends. They include the Stikine arch fault complex – the Pitman fault and unnamed faults associated with Red Chris and GJ (ca 203 Ma), and North ROK (ca 222 Ma); the Iskut-Verrett fault and Bronson corridor, which hosts the Snip mine and Red Bluff stock (ca 195 Ma); and Skeena arch structures, which form the loci of the Kleanza and Howson Range plutons (212-178 Ma). All of these structural corridors were subsequently reactivated, some during mid-Jurassic accretion, others during mid-Cretaceous Skeena fold and thrust belt sinistral transpressive deformation. They are, however, old: the north-south structures affected some of the oldest geological processes of Stikinia – emplacement of the Devonian-Mississippian More Creek and Forrest Kerr plutons, and development of the Tulsequah Chief VMS orebodies (ca 325 Ma). They may have formed by crustal extension during initiation of the pericratonic Yukon-Tanana-Stikinia arc and subsequent slab rollback , with the east-west structures as accompanying transforms. Once established, these zones would focus strain under a variety of stress regimes. Triassic-Jurassic tectonics favored mild, transient transtension on both northerly and easterly orientations, which led to episodic magma ascent and porphyry mineralization.