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Volcanostratigraphy, age and geologic setting of the Lower-Middle Jurassic Upper Hazelton Group, west-central British Columbia Gordee, Sarah Marie

Abstract

Lower and Middle Jurassic Hazelton Group rocks on the southwest margin of the Stikine Terrane (Stikinia) of the Canadian Cordillera are part of a widespread Early-Middle Jurassic arc assemblage. Upper Hazelton Group volcano-sedimentary strata host the world class, precious metal-enriched, polymetallic Eskay Creek volcanogenic massive sulphide (VMS) deposit in northwest Stikinia, as well as a number of epithermal and porphyry deposits in associated subvolcanic intrusions throughout central and northern Stikinia. Large segments of Hazelton Group strata are understudied, despite significant mineral potential. In southwest Stikinia, upper Hazelton Group strata are in part coeval with volcano-sedimentary strata that host the Eskay Creek deposit. The lithologic sequence in southwest Stikinia consists of late Early Jurassic mafic volcanic centre(s) overlain by a Middle Jurassic, sequence of volcanic vent-proximal, felsic volcanic strata, and associated reworked volcanic material. Volcanic textures, sedimentary structures and fossils together indicate dominantly shallow submarine deposition. Lithogeochemical studies indicate a normal, subduction-related affinity for Hazelton Group strata in southwest Stikinia, which contrasts with a more primitive, rift-related(?) affinity for the strata in the Eskay Creek VMS district in northwest Stikinia. Hazelton Group rocks in the Eskay Creek region and coeval rocks in southwest Stikinia were probably deposited within a broad submarine basin in the back-arc region of a Middle Jurassic oceanic island arc. Rocks of the Eskay Creek VMS district were probably deposited in a localised back-arc rift in a relatively deeper marine setting. Despite differences in the depositional environment and tectonic setting of the two regions, volcano-sedimentary sequences in southwest Stikinia demonstrate significant potential for contained VMS mineralisation.

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