METALLOGENY OF AN EARLY TO MIDDLE JURASSIC ARC, ISKUT RIVER AREA, NORTHWESTERN BRITISH-COLUMBIA

The Iskut River area of northwestern British Columbia is a relatively small (approx 100 x GO km) but metallogenetically significant portion of the Canadian Cordillera. In the Iskut River area, Mesozoic volcanic -are rocks and related intrusions of the Stikine terrane are host to a wide variety of mineral deposits, most of which formed in Early to Mi ddle Jurassic time. Porphyry-style mineralization includes the Kerr Cu -Au porphyry deposit, the Mitchell-Sulphurets porphyry deposits, and t he Red Bluff prospect, all related to calc-alkaline to subalkaline Ear ly Jurassic intrusions. Precious metal-rich veins at the Johnny Mounta in and Snip mines are spatially and genetically associated with the Re d Bluff intrusion. These deposits show a progression from shear-hosted laminated mesothermal veins at deeper levels (Snip mine) to thick, ta bular dilational veins at higher levels (Johnny Mountain mine). In the Sulphurets camp, vein-hosted mineralization of the west zone exhibits a variety of vein textures suggesting a relatively shallow level of f ormation. The timing and stratigraphic setting of advanced argillic al teration at the Treat): Glacier prospect indicates near-surface format ion. Finally, the Eskay Creek mine is presently producing from high-gr ade, precious and base metal volcanic massive sulfide-sulfosalt minera lization that formed on the sea floor in the Middle Jurassic. In addit ion, several other styles of mineralization are recognized in the Isku t area including the Triassic Granduc volcanogenic massive sulfide dep osit, gold-rich skarns such as McLymont Creek of probable Early Jurass ic age, and gabbro-hosted magmatic nickel sulfide mineralization at Ni ckel Mountain of uncertain age. Integrated regional mapping, deposit-s pecific studies, geochronology, lithogeochemistry, and biostratigraphy have demonstrated that Early to Middle Jurassic mineralization develo ped within the evolving Hazelton Group Volcanic arc. Volcanism during early stages of are evolution (similar to 200-180 Ma) is characterized by calc-alkaline andesites to dacites. Most Jurassic intrusions in th e region are coeval with this episode of volcanism and are dominated b y a potassium feldspar megacrystic suite of granitic to granodioritic plutons. Mineralization which is temporally and spatially associated w ith this period of magmatism includes porphyry-style deposits and prec ious metal-rich vein systems, which often show strong structural local ization. A younger period of volcanism (similar to 180-170 Ma) is bimo dal (rhyolite-dacite and basalt-basaltic andesite and contains both ca lc-alkaline and tholeiitic signatures. Mineralization during this late r stage of the are includes high-level alteration systems and submarin e exhalative mineralization. Regional contractional deformation in mid -Cretaceous lime resulted in significant structural modification of in dividual deposits, obscuring many of the primary field relationships.