Geoscience Map 1993-4: Geology of the Scud Glacier Area, Northwestern B.C.
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Geoscience Map 1993-4 presents the geology and mineral occurrences of the Scud Glacier area (104G/06) in northwestern British Columbia. The 1:50 000 scale geological map includes a legend, geological cross sections, references, and a reference source inset map.
Stikine assemblage strata range in age from Upper Carboniferous to Lower Permian. Upper Carboniferous strata include a unit with foliated, pyroxene-feldspar phyric andesitic flows and sills, crystal tuff, lithic lapilli tuff and recrystallized limestone; and a unit with foliated argillite, siltstone, calcareous siltstone, conglomerate and recrystallized limestone. A Paleozoic or Upper Triassic unit consists of massive to foliated siltstone, conglomerate, andesite, and tuff. Upper Carboniferous to Lower Permian strata are mainly bedded to laminated sericitic ash tuff and tuffaceous siltstone, chert, and calcareous siltstone. Lower to Upper Permian strata include a unit that is mainly pyrite and pyrrhotite-bearing argillite and siltstone, calcarenite unit with minor chert layers and nodules, and a maroon tuffaceous limestone unit.
Upper Triassic and possibly older metamorphic rocks may be Stuhini Group equivalents. They consist of massive to foliated metavolcanics, biotite schist, chert, chlorite schist and siliceous rock. Stuhini Group strata consist of a lower unit dominated by volcanic rocks that contains pyroxene-phyric flows and breccias, epiclastics, limestone, phyllite and conglomerate; and an upper unit with mainly sedimentary rocks including sandstone, siltstone, argillite and limestone lenses. Lower to Middle Jurassic Hazelton Group is represented by polymictic conglomerate.
Middle to Late Triassic olivine clinopyroxenite, dunite and gabbro comprise the oldest intrusive rocks in the area. The Middle to Late Triassic Stikine Suite intrusions consist of gabbro and hornblendite, quartz monzonite, biotite granodiorite, monzodiorite, quartz diorite, diorite and plagioclase megacrystic quartz diorite. The Late Early Jurassic Cone Mountain Suite intrusions are granodiorite and quartz monzodiorite. The Middle Jurassic Three Sisters Suite contains mainly hornblende biotite granite. The Eocene Hyder Suite of intrusions includes biotite granite that is locally potassium feldspar-megacrystic, hornblende-biotite granodiorite, megacrystic granodiorite, and felsite. Chlorite-altered plagioclase phyric granodiorite is Tertiary (or Early Jurassic). Tertiary and older dikes are andesite, basalt, felsite, olivine basalt, rhyolite and syenite.
Structural style in the area is dominated by brittle deformation and faulting and controlled by competency contrasts between volcanic and sedimentary rocks. Three or possibly four episodes of deformation have been recognized, but ages are poorly constrained. The earliest structures are synmetamorphic, and pre-Triassic, possibly Carboniferous, age.
These structures, and related northeast-striking penetrative foliations, are deformed by west-trending post-Triassic (?) folds. Northerly-trending southwest-verging folds and contractional faults are post-Early Jurassic, and extensional faults are at least in part of Tertiary age.
Metallogeny in the area is related to plate boundary subduction processes and two separate mineralizing events, one in the latest Late Triassic and one in the Eocene. Each is characterized by a different base and precious metal suite. A Late Triassic to Early Jurassic alkalic volcanic centre at Galore Creek, to the south, hosts ten synvolcanic copper-gold deposits.
The largest, the Stikine Copper Limited central zone contains 125 000 000 tonnes of material with an estimated grade of 1.06 per cent copper, 0.4 gram per tonne gold and 7.7 grams per tonne silver. A similar deposit occurs at Copper Canyon. Pervasive potash metasomatism and retrograde calcsilicate alteration characterize the mineralized zones. The large calcalkaline Schaft Creek copper deposit is located in the adjacent map area to the east. Reserves at Schaft Creek are 900 million tonnes at 0.30 per cent copper and values in gold and silver. Smaller tonnage, Eocene silver-rich base metal veins are associated with calcalkaline intrusions and hosted in northeasterly-striking faults. Alteration and gangue minerals are quartz, sericite, and iron carbonate assemblages. Volcanogenic massive sulphide deposits (e.g., Tulsequah Chief) are an untested but viable exploration target in the Paleozoic Stikine assemblage rocks.
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