| Titre | Magnetite as an Indicator Mineral in the Exploration of Porphyry Deposits: A Case Study in Till near the Mount Polley Cu-Au Deposit, British Columbia, Canada |
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| Auteur | Pisiak, L K; Canil, D; Plouffe, A ; Ferbey, T; Lacourse, T |
| Source | Economic geology and the bulletin of the Society of Economic Geologists vol. 112, 2017 p. 919-940, https://doi.org/10.2113/econgeo.112.4.919  Accès ouvert |
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| Année | 2017 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20170019 |
| Éditeur | Society of Economic Geologists |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.2113/econgeo.112.4.919 |
| Media | numérique; en ligne |
| Formats | pdf |
| Province | Colombie-Britannique |
| SNRC | 93A/05; 93A/06; 93A/11; 93A/12 |
| Région | Quesnel Lake |
| Lat/Long OENS | -121.9167 -121.4167 52.6667 52.4167 |
| Sujets | magnetite; roches ignées; roches métamorphiques; gisements porphyriques; géochimie des dépôts glaciaires; géochimie du sol; géochimie de l'eau de cours d'eau; géochimie du till; géochimie des éléments en
trace; méthodes de dépistage des sédiments; tills; géochimie des éléments en trace; éléments d'indice; roches intrusives felsiques; géologie économique; géochimie; minéraux métalliques; sédimentologie; Trias; Jurassique |
| Illustrations | cartes de localisation; cartes géologiques généralisées; photographies; photomicrographies; graphiques |
| Diffusé | 2017 04 03 |
| Résumé | (disponible en anglais seulement)
The investigation of this paper focused on whether the composition of hydrothermal ore-related magnetite in till could be used to locate porphyry deposits in
terrane where glacial overburden overlies rocks that host porphyry Cu-Au mineralization. This hypothesis was tested using 20 till samples collected in a ~900-km2 area surrounding the Mount Polley porphyry Cu-Au deposit in south-central British
Columbia, Canada. At least 100 magnetite grains were randomly selected from the magnetic fraction of each till sample. Nineteen trace elements in ~50 magnetite grains in each sample were measured by laser ablation-inductively coupled plasmamass
spectrometry (LA-ICP-MS). The large beam or raster size used for laser ablation (to 100 mm) homogenizes any heterogeneous trace element distributions in magnetite that result from oxy-exsolution and/or and dissolution/reprecipitation, avoiding this
issue with the few micron size of an electron beam. Linear discriminant analysis (LDA) performed on a compilation of magnetite compositions measured by LA-ICP-MS from worldwide porphyry deposits and intrusive igneous rocks define the chemical
signature (Mg, Al, Ti, V, Mn, Co, Ni) of hydrothermal magnetite exclusive to porphyry systems. Application of our two LDA models to the 985 magnetite compositions we measured in the till samples surrounding Mount Polley showed anomalous amounts of
hydrothermal magnetite grains in till up to 2.5 km west-southwest and 4 km northwest of the deposit-a pattern that is consistent with the ice-flow history of the region. Our LDA models for magnetite trace element compositions have strong potential to
be an effective tool in exploration for buried porphyry systems. |
| GEOSCAN ID | 300538 |
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