Geoscience Map 1993-1: Geology and Mineral Occurrences of the Galore Creek Area
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Scale 1:50 000
Geoscience Map 1993-1 presents the geology and mineral occurrences of the Galore Creek area (104G/03). The 1:50 000 scale geological map includes a legend, four geological cross sections, and a reference list.
Stikine assemblage strata range in age from Devonian to Permian. Devonian to Lower Carboniferous strata include units dominated by quartz sericite schist; limestone; and mafic and felsic flows, and intermediate crystal tuff, breccia and flows. Lower Carboniferous rocks include grainstone with chert interbeds and packstone with tuff and epiclastic interbeds. Upper Carboniferous to Lower Permian units are mainly conglomerate, siliceous siltstone and felsic dust tuff, and volcaniclastic rocks. Lower Permian strata include bioclastic grainstone, epiclastics and tuff.
Lower Triassic siliceous and limy siltstones are overlain by carbonaceous silty shale of Middle Triassic age. Upper Triassic Stuhini Group units include silicic clastics and volcanic wackes; siltstone, sandstone and augite crystal tuffs and flows; plagioclase and basaltic –andesite and hornblende porphyry flows and tuffs; intermediate breccia flows, lahar and fragmentals; fine black clastics, tuff and conglomerate; and pyroxene porphyry breccia flows.
Upper Triassic to Lower Jurassic strata comprise a volcanic facies, with potassium-feldspar and pseudoleucite-bearing fragmentals and alkaline basalt flows, and a sedimentary facies with potassium-feldspar crystal tuff, epiclastics and volcanic conglomerate. Lower Jurassic strata include a unit of polymictic volcanic conglomerate, siltstone, shale and airfall tuff, and a unit of mainly felsic tuffite.
The oldest intrusive rocks are Late Devonian hornblende diorites. Middle to Late Triassic intrusions include ultramafic rocks, with gabbro and pyroxenite bodies, and granodiorite to monzonite of the Hickman batholith. The Late Triassic to Early Jurassic Galore Creek intrusions consist of syenite, and porphyritic monzonite. Early Jurassic intrusions are quartz diorite and granodiorite, and porphyritic diorite may be Early Jurassic or younger. Eocene intrusions are granodiorite, and potassium feldspar-megacrystic granite and equigranular quartz monzonite.
Structural style at Galore Creek is dominated by brittle deformation and faulting and controlled by competency contrasts between volcanic and sedimentary rocks of the arc assemblage. 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. Two post-Early Jurassic events are recognized, one is characterized by north-trending southwest-verging folds and reverse faults; and the younger is characterized by northeast-verging kink folds.
Metallogeny in the Galore 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 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 at the Trek property and breccia-pipes at the Ptarmigan zone. 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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