THE STUHINI – HAZELTON UNCONFORMITY OF STIKINIA, INVESTIGATIONS AT KSM- BRUCEJACK, SNIP- JOHNNY MOUNTAIN AND RED CHRIS AREAS

Within the Stikine terrane of northwestern BC, clusters of Triassic-Jurassic mineral occurrences, including several large porphyry copper-gold deposits, are located within 2 km of the contact of the Triassic Stuhini Group and Jurassic Hazelton Group . The contact approximates a level of exposure of the volcanic pile and more importantly, the paleotopography and related depositional environment at the onset of Hazelton volcanism. It varies from a sharp, angular unconformity, where the Hazelton Group overlays folded and strongly deformed Stuhini group, to a subtle (~15^o strike) difference in bedding. The unconformity represents a Late Triassic hiatus of volcanism, during which the Stikine terrane underwent significant structural tectonic change and deformation, resulting in crustal pre-conditioning. To identify crustal preconditioning and specific structures that were exploited by mineralised systems, cross-sections transecting the Stuhini-Hazelton contact have been documented in detail in three mineral districts: Brucejack-KSM, Snip –Johnny Mountain and Red Chris. Although each district is unique, common themes include contractional deformation of the Stuhini Group succeeded by mild extension or transtension at the onset of the younger, more mineralized magmatic episode; and the key role of long-lived structures in the formation of economic deposits.