Geology and geochemistry of the Eagle Bay Assemblage in the Johnson Lake area, Kootenay Terrane, South-central British Columbia
Date
2002
Authors
Bailey, Sean L.
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Abstract
1: 20,000 scale geological mapping of the Eagle Bay Assemblage was conducted in the Johnson Lake area in southern British Columbia to document lithologies that host economically important base and precious metal deposits. The Eagle Bay Assemblage consists of polydeformed, greenschist metamorphic grade rocks derived from volcanic, intrusive and sedimentary protoliths, and is assigned to the pericratonic Kootenay Terrane of the Canadian Cordillera.
Lower Cambrian ( and older?) metamorphosed bedded chert, siliciclastic, mafic volcanic/ volcaniclastic rocks and limestone structurally overlie Devonian-Mississippian felsic, intermediate and mafic volcanic/volcaniclastic and siliciclastic rocks. Geological units and structures trend northwest, and dip east. The geometries are controlled predominantly by Jurassic west-verging folding and thrusting. Folds are tight to isoclinal with overturned limbs, have synmetamorphic axial planar cleavage and developed synchronously with thrust faulting. Fault geometries can be explained by treating the thrusts as a series of ramps and flats. Thrust flats trend northwest and dip moderately east concordant with stratigraphic layers. Ramps trend north, dip steeply east and cut across stratigraphic layers. Late Devonian felsic to intermediate volcanic rocks and subvolcanic intrusions have calk-alkalic whole rock geochemistry and are assigned to a volcanic arc tectonic setting. Structurally overlying these rocks are alkalic intermediate to felsic rocks that yield a 36064.6 Ma U-Pb zircon age. These rocks are interpreted to have formed during rifting of the volcanic arc. Mafic volcanic rocks overlying the Rea and Sarritosum deposits are of uncertain age and have an ocean island basalt (OIB) rift type chemistry.
Mafic volcanic rocks of known Lower Paleozoic age have OIB and mid ocean ridge basalt (MORB) type chemistry and are remnants of a continental margin rift. Late Devonian rocks host volcanogenic massive sulphide (VMS; Rea, K7, Homestake) and quartz-carbonate-sulphide vein (Samatosum) deposits. The Homestake massive barite/sulphide deposit is hosted within altered felsic volcanic rocks of unit 6. The Rea and Samatosum deposits occur within a fault repeated altered argillite and quartz-wacke that is truncated to the south. However this zone continues northwest of the map area and may host undiscovered massive sulphide deposits.