Geoscience Map 1993-3: Geology of the Scud River Area, Northwestern B.C.
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Scale 1:50 000
Geoscience Map 1993-3 presents the geology and mineral occurrences of the Scud River area (104G/05) in northwestern British Columbia. The 1:50 000 scale geological map includes a legend, geological cross sections, 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 possibly Upper Carboniferous 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, and a calcarenite unit with minor chert layers and nodules.
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. Volcanic rocks represent the Upper Triassic Stuhini Group.
The Late Triassic to Early Jurassic Copper Mountain Suite intrusions are the oldest intrusive rocks in the area. They consist of megacrystic quartz monzonite, equigranular to megacrystic syenite, and clinopyroxenite. Early Jurassic (?) quartz diorite, hornblende diorite, hornblendite and pyroxenite comprise the Diorite Suite. 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. 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.
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. 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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