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TitleTesting the relationship between the Llewellyn fault, Tally-Ho shear zone, and gold-mineralization in northwest British Columbia
AuthorOotes, L; Castonguay, SORCID logo; Friedman, R; Devine, F; Simmonds, R
SourceGeological fieldwork 2017: a summary of field activities and current research; British Columbia Ministry of Energy and Mines, British Columbia Geological Survey Paper 2018-1, 2018 p. 67-81 Open Access logo Open Access
LinksOnline - En ligne
Alt SeriesNatural Resources Canada, Contribution Series 20170305
PublisherBritish Columbia Ministry of Energy, Mines and Petroleum Resources
Mediapaper; on-line; digital
File formatpdf
ProvinceBritish Columbia; Yukon
NTS104M/07; 104M/08; 104M/09; 104M/10; 104M/11; 104M/12; 104M/13; 104M/14; 104M/15; 104M/16; 105D/01; 105D/02; 105D/03; 105D/04; 105D/05; 105D/06; 105D/07; 105D/08
AreaEngineer; Montana Mountain; Mount Skukum; Tutshi Lake; Moon Lake; Racine Lake; Taglish lake; Bennett Lake; Mount Hodnett; Middle Ridge
Lat/Long WENS-135.5833 -134.0000 60.3667 59.2500
Subjectseconomic geology; structural geology; tectonics; geochronology; mineral deposits; mineral exploration; epithermal deposits; mesothermal deposits; gold; ore mineral genesis; mineralization; ore controls; structural controls; bedrock geology; structural features; faults; folds; shear zones; lithology; igneous rocks; intrusive rocks; granodiorites; granites; volcanic rocks; rhyolites; sedimentary rocks; metamorphic rocks; marbles; monzonites; amphibolites; mylonites; tectonic history; metamorphism; deformation; foliation; lineations; intrusions; plutons; dykes; radiometric dating; uranium lead dating; zircon dates; crustal structure; mineral occurrences; mass spectrometer analysis; Llewellyn Fault; Tally-Ho Shear Zone; Nisling Terrane; Boundary Ranges Metamorphic Suite; Stuhini Group; Laberge Group; Whitehorse Plutonic Suite; Stikinia Terrane; Yukon-Tanana Terrane; Sloko Group; Windy Table Coplex; Carmacks Group; Bennett Granite; Lewes River Group; Povoas Formation; Engineer Mine; Phanerozoic; Cenozoic; Tertiary; Mesozoic; Cretaceous; Jurassic; Triassic; Paleozoic
Illustrationsgeoscientific sketch maps; photographs; cross-sections; Concordia diagrams; bar graphs; tables; geological time charts
ProgramTargeted Geoscience Initiative (TGI-5) Gold systems
Released2018 01 01
AbstractThe Llewellyn fault represents a significant geological feature in northwest British Columbia. The fault is a southeast-striking, steeply dipping brittle dextral strike-slip structure that overprints 'early' ductile deformation, which is preserved as foliations, lineations, and folds in the host rocks. The Tally-Ho shear zone, Yukon, shares similar early ductile deformation and is overprinted by the Llewellyn fault. In general, the deformation corridor demarcates the eastern limit of metamorphic suites (Triassic and older rocks of the Nisling terrane and Boundary Ranges metamorphic suite) and the western limit of the younger Stuhini (Triassic) and Laberge (Jurassic) groups. Previous work and this study demonstrate that brittle strike-slip deformation along the Llewellyn fault occurred between ca. 56 and 50 Ma. New field observations indicate the early ductile deformation is represented by one foliation (S(main)) along the Llewellyn fault and Tally-Ho shear zone corridor. Two granodiorite intrusions crosscut the early deformation features, and new U-Pb zircon chemical abrasion ID-TIMS results indicate they crystallized at ca. 75 Ma. In the Tally-Ho shear zone, the S(main) is parallel to a foliation in an adjacent granodiorite, mapped as part of the Whitehorse plutonic complex (ca. 120 Ma). In British Columbia, a deformed rhyolite along the Llewellyn fault yielded a preliminary ca. 120 Ma age. Based on these results, we infer that the early ductile fabrics formed before ca. 75 Ma and, potentially, after ca. 120 Ma.
A goal of this study was to establish if the early ductile and late brittle structures represent a crustal-scale, ductile-brittle deformation continuum. If so, could various gold mineralization styles (epithermal, mesothermal, intrusion-related) along the structural corridor be related in time and be part of an orogenic gold mineralizing system? This study demonstrates that, although the early ductile and late brittle deformation share the same space, they developed at least ca. 20 Ma apart and are not part of a structural continuum. This result indicates the various styles of gold mineralization developed during temporally distinct tectonic events.
Summary(Plain Language Summary, not published)
This report presents the preliminary results of a study of the relationship between the Llewellyn and Tally Ho fault zones in northern British Columbia and southern Yukon. Several styles of gold mineralization are spatially associated with these fault zones. The genetic and temporal relationships between these structures, Eocene volcanism and gold deposits and showings are studied using fieldwork and geochronological analyses.

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