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TitleGeology of the Eocene Ootsa Lake Group in northern Nechako River and southern Fort Fraser map areas, central British Columbia
DownloadFree download (whole publication) (pdf 116617 KB)
AuthorGrainger, N C; Anderson, R G
SourceCordillera and Pacific margin / Interior Plains and Arctic Canada/Cordillère et marge du Pacifique / Plaines intérieures et régions arctique du Canada; by Geological Survey of Canada; Geological Survey of Canada, Current Research no. 1999-A/B, 1999 p. 139-148,
PublisherNatural Resources Canada
RelatedThis publication is contained in Geological Survey of Canada; Geological Survey of Canada; (1999). Cordillera and Pacific margin / Interior Plains and Arctic Canada, Geological Survey of Canada, Current Research no. 1999-A/B
ProvinceBritish Columbia
NTS93F/11; 93F/12; 93F/13; 93F/14
AreaDayeezcha Mountain; Henson Hills; Mackenzie Lake; Ootsa Lake; Binta Lake; Uncha Mountain
Lat/Long WENS-126.0000 -125.0000 54.0000 53.5000
Subjectsigneous and metamorphic petrology; structural geology; stratigraphy; Eocene; volcanic rocks; rhyolites; tuffs; pyroclastics; dacites; andesites; textural analyses; igneous rocks; lithology; field relations; stratigraphic analyses; potassium argon dates; argon argon dates; uranium lead dates; radiometric dates; bedrock geology; plutonic rocks; monzo-granites; Ootsa Lake Group; Tertiary
Illustrationssketch maps; photographs
ProgramNechako NATMAP Project
Released1999 02 01
AbstractEocene Ootsa Lake Group in northern Nechako River map area comprises variegated, flow-laminated rhyolitic flows and domes, crystal and lithic-crystal tuff, less common pyroclastic and autoclastic breccia, and minor dacite and andesite flows. Rotated rhyolite clasts, flow folding, vesicles, perlite and spherulites, and minor lithophysae and eutaxitic textures and phenocrysts of plagioclase, biotite, alkali feldspar, quartz, and rare hornblende are distinctive.
A local stratigraphy comprises basal hornblende-plagioclase porphyritic andesite with distinctive amethyst-bearing amygdules, medial flow- laminated rhyolite flow rocks and breccia, and upper felsic tuff and breccia. Distinct rhyolite ash-lignite beds mark the top of the unit and in addition to glassy quenched flow bases and reworking of lithic rhyolite tuff units, suggest local shallow-water environments.
The Dayeezcha Mountain, Henson Hills, and Mackenzie Lake study areas provide the most complete stratigraphy. Ongoing petrographic, geochronological, geochemical, and isotopic tracer studies will elucidate the age, correlation, composition, tectonic setting, and petrogenesis of the unit.