EVOLVING IDEAS ON THE JURASSIC TECTONIC HISTORY OF NORTHWESTERN STIKINIA, CANADIAN CORDILLERA

At least 5 significant Paleozoic to Paleogene tectono-stratigraphic assemblages and associated mineral deposits characterize NW Stikinia in the Canadian Cordillera. Multiple and overlapping Devonian, Carboniferous and Triassic arc assemblages are basement to the Jurassic arc and basinal assemblages and all predate intrusion by the Paleogene Coast Plutonic Complex.

Previous work and new regional mapping, stratigraphic studies, biochronology, and geochronology studies by numerous workers of volcanic, sedimentary and plutonic rocks are combined to develop new ideas on the Jurassic stratigraphies and tectonics. The studies help define the character and nature of transition between a Lower to Middle Jurassic arc, separate and west-facing Middle Jurassic arc-back arc-basinal system, and onset of Lower to Middle Jurassic successor basin development. The two arc complexes host an abundant and diverse metallogeny, the most prominent example being the well-studied base and precious metal Eskay Creek deposit, presently being mined. As well, they test potential correlation of cospatial mineral deposits.

Jurassic tectonics comprises at least 4 magmatic episodes, formation of 3 sedimentary basins, and at least 3 mineralizing events. Triassic-Jurassic, Early Jurassic, Middle Jurassic, and Cretaceous-Eocene deformations bracket magmatic and mineralizing events. Development of the alkaline to subalkaline, calc-alkaline to tholeiitic, isotopically-primitive Jurassic island arcs resolve into four ca. 5-10 m.y. magmatic episodes between 200 Ma and 170 Ma. The episodes and associated mineral deposits include: 1) latest Triassic-Early Jurassic (Hettangian-Sinemurian and ca. 205-196 Ma) alkaline porphyry-related, deformed mesothermal Ag-Au veins as at Red Mountain; 2) Early Jurassic (Pliensbachian-Toarcian and ca. 196-187 Ma) alkaline porphyry-related epithermal and mesothermal Ag-Au veins and base and precious metal deposits as at Premier, Sulphurets, and Bronson Creek; 3) Early to Middle Jurassic (ca. 185-183 Ma) unnamed, small and poorly mineralized porphyry intrusions; and 4) Middle Jurassic (Aalenian-Bajocian and ca. 175-172 Ma) calc-alkaline arc and tholeiitic back-arc magmatism and syn- and epigenetic, stratabound base and precious metal deposits (e.g., Eskay Creek deposit and RDN prospect?) related to the back-arc basin formation.