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TitreMagnetite as an indcator mineral in porphyry Cu±Au±Mo deposits of British Columbia, Canada
AuteurCanil, D; Pisiak, L; Lacourse, T; Plouffe, A; Ferbey, T; Grondahl, C
SourceIndicator minerals in till and stream sediments of the Canadian Cordillera; par Ferbey, T (éd.); Plouffe, A (éd.); Hickin, A S (éd.); Geological Association of Canada, Special Paper vol. 50, 2017 p. 161-174
Séries alt.Ressources naturelles Canada, Contribution externe 20180026
Séries alt.Mineralogical Association of Canada, Topics in Mineral Sciences 47
ÉditeurAssociation géologique du Canada
ÉditeurAssociation minéralogique du Canada
Documentpublication en série
Référence reliéeCette publication est contenue dans Ferbey, T; Plouffe, A; Hickin, A S; (2017). Indicator minerals in till and stream sediments of the Canadian Cordillera, Geological Association of Canada, Special Paper vol. 50
SNRC82; 83; 84; 92; 93; 94; 102; 103; 104; 114
Lat/Long OENS-141.0000 -113.0500 60.0000 48.0000
Sujetsgisements minéraux; prospection minière; techniques de prospection; exploration de dépôts glaciaires; gisements porphyriques; cuivre; or; molybdène; dépôts glaciaires; tills; échantillons de till; magnetite; système hydrothermal; géologie du substratum rocheux; lithologie; roches ignées; roches intrusives; analyses des éléments en trace; analyse par spectromètre de masse; analyses thermiques; analyses statistiques; analyses discriminantes; analyses pétrographiques; établissement de modèles; anomalies; antecedents glaciaires; glaciation; déglaciation; écoulement glaciaire; Cordillère canadienne; Ceinture d'Intermontane ; Terrane de Stikinia ; Terrane de Quesnellia ; Ceinture d'Insular ; Terrane de Wrangellia ; directions d'écoulement glaciaire; géologie économique; géologie des dépôts meubles/géomorphologie; géomathématique; minéralogie; Phanérozoïque; Cénozoïque; Quaternaire; Mésozoïque
Illustrationsgeoscientific sketch maps; photographs; photomicrographs; plots
ProgrammeInitiative géoscientifique ciblée (IGC-5), Systèmes porphyriques
ProgrammeInitiative géoscientifique ciblée (IGC-4)
ProgrammeCRSNG Conseil de recherches en sciences naturelles et en génie du Canada
Résumé(disponible en anglais seulement)
Glacial overburden can overlie large areas of Mesozoic intrusive igneous rocks in the Canadian Cordillera that potentially host porphyry Cu-Au mineralization. Magnetite is an accessory mineral in many such deposits, and once eroded from these sources by glacial action and transport, may serve as a useful indicator mineral for prospecting in glaciated terrain. Previous work shows that magnetite from ore deposits has a trace element signature that is unique from that of a common accessory mineral in igneous or metamorphic rocks. To this end we review the geochemical characteristics of magnetite of hydrothermal origin from porphyry deposits in British Columbia. We observe much heterogeneity at the grain and deposit scale for many trace elements (Mo, Cu, Sn, Mn, V, Sc, Ni) in magnetite from five porphyry deposits. Hydrothermal magnetite is consistently low in elements that are temperature-sensitive in the spinel structure (Ti, Al, Mg), and is rich in Sn and sometimes Mo, relative to Sc. A linear discriminant analysis (LDA) of magnetite compositions compiled from worldwide porphyry deposits and intrusive igneous rocks (n=481) permits a rigorous definition of the chemical signature of hydrothermal magnetite from such systems in terms of its Mg, Al, Ti, V, Mn, Co, and Ni contents.
We review an application of magnetite composition as a vector to locate porphyry deposits in glaciated terrain, using 20 subglacial till samples collected in a 900 km2 area surrounding the Mount Polley porphyry Cu-Au deposit, in south-central British Columbia. Twenty trace elements were measured by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in 50 magnetite grains from each till sample. Application of our LDA models to magnetite populations in the till samples shows that anomalous concentrations of hydrothermal magnetite grains are detected in till up to 2.5 km west-southwest and 4 km northwest of the Mount Polley deposit. The dispersal direction of these grains is consistent with the ice-flow history of the region. The use of LDA to identify hydrothermal magnetite has a strong potential to be an effective indicator in exploration for buried porphyry systems in British Columbia and elsewhere. Further tests of this exploration method should be performed around other known sources of porphyry Cu±Au±Mo mineralization with different ice-flow histories. In addition, improvements to the LDA models we developed for hydrothermal magnetite identification will be possible with more analyses from other porphyry deposits.