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TitreA new lode gold discovery at Otter Creek: another source for Atlin placers
AuteurMihalynuk, M G; Zagorevski, A; Devine, F A M; Humphrey, E
SourceBritish Columbia Ministry of Energy and Mines, British Columbia Geological Survey Paper no. 2017-1, 2016 p. 179-193
LiensOnline - En ligne
Année2016
Séries alt.Secteur des sciences de la Terre, Contribution externe 20160313
ÉditeurBritish Columbia Ministry of Energy and Mines
Documentpublication en série
Lang.anglais
Mediapapier; en ligne; numérique
Formatspdf
ProvinceColombie-Britannique
SNRC104N/12
Lat/Long OENS-133.5000 -133.1667 60.0000 59.7500
Sujetsgisements alluvionnaires; or; érosion; gisements alluvionaires, ruisseau; cassitérite; thorite; batholites; Batholite de Surprise Lake ; Batholite de Fourth Of July ; Formation de Kedahda ; Terrane de Cache Creek
Illustrationslocation maps; geological sketch maps; photographs; graphs; photomicrographs
ProgrammeRedéfinition des blocs de la croûte terrestre de l'ouest de la Cordillère, GEM2 : La géocartographie de l'énergie et des minéraux
Résumé(disponible en anglais seulement)
Primary exploration targets for lode gold near Atlin, northwestern British Columbia have historically been quartz-carbonate-mariposite altered (¿listwanite¿) ultramafic and mafic bedrocks. These have long been considered the source of nearby placer deposits, and locally do contain fine visible gold. However, despite more than a century of searching, coarse gold such as found in the placer gravels has never been discovered. This has prompted the belief that the "listwanites" are mere erosional remnants of bedrock sources of the coarse placer gold, and that these sources have been almost entirely lost to erosion. An alternative hypothesis argues that, although gold is found with listwanite, it was not the only bedrock source. Streams with placer deposits are distributed around the evolved Surprise Lake batholith (Sn-U-Th-Mo-W-F rich) and rare gold nuggets contain Sn- and Th-rich mineral intergrowths (cassiterite and thorite), demonstrating that at least some of the placer gold may be related to the batholith. Discovery of coarse lode gold (>5 mm) in graphitic and quartz-rich phyllitic bedrock beneath placer deposits along Otter Creek in 2016 confi rms that listwanite-altered mafic and ultramafic rocks are not required for lode gold mineralization. At the discovery site, native gold is intergrown with quartz-albite veins and occurs as open space fillings. Rutile in quartz veins, and perhaps altered titanite in the adjacent phyllite may have grown along with gold deposition. Geochemical analysis of pyrite-rich phyllite adjacent to the gold veins yields no appreciable gold, but is slightly elevated in Cu (11-54 ppm), Pb (~33 ppm) and zinc (60-70 ppm). These results are consistent with petrographic observations that show abundant chalcopyrite inclusions but no gold inclusions in pyrite. Discovery of coarse gold in quartz veins cutting graphitic and quartz-rich phyllitic country rocks significantly expands the lode gold exploration target in the Atlin placer camp.
Résumé(Résumé en langage clair et simple, non publié)
Le présent rapport présente les résultats préliminaires et les modèles mis au point dans le cadre du programme GEM2 sur les roches volcaniques et plutoniques en Colombie-Britannique. Il indique en détail l'âge et les caractéristiques des roches magmatiques et de la minéralisation associée d'après des analyses effectuées sur le terrain et en laboratoire. Les résultats qui y sont présentés contribuent au perfectionnement du modèle GEM2, dont le but ultime est de redéfinir les modèles tectoniques régionaux de la Cordillère.
GEOSCAN ID299632