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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dc.contributor.authorPisiak, L.K.
dc.contributor.authorCanil, Dante
dc.contributor.authorLacourse, Terri
dc.contributor.authorPlouffe, A.
dc.contributor.authorFerbey, T.
dc.date.accessioned2018-09-27T18:55:33Z
dc.date.available2018-09-27T18:55:33Z
dc.date.copyright2017en_US
dc.date.issued2017
dc.description.abstractThe 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 μm) 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.en_US
dc.description.reviewstatusRevieweden_US
dc.description.scholarlevelFacultyen_US
dc.description.sponsorshipWe thank J. Spence for assistance with LA ICPMS analyses. Till collection and sample processing was supported by Natural Resources of Canada Targeted Geoscience Initiative 4 grants to AP and TF. LP was supported by student scholarships from Geoscience BC, the University of Victoria and the Society for Economic Geologists. Analytical work was supported by British Columbia Ministry of Energy and Mines and NSERC of Canada Discovery grants to DC.en_US
dc.identifier.citationL.K. Pisiak, D. Canil, T. Lacourse, A. Plouffe, T. Ferbey (2017). 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. Economic Geology, 112(4), 919-940. https://doi.org/10.2113/econgeo.112.4.919en_US
dc.identifier.urihttps://doi.org/10.2113/econgeo.112.4.919
dc.identifier.urihttp://hdl.handle.net/1828/10107
dc.language.isoenen_US
dc.publisherEconomic Geologyen_US
dc.subjectBritish Columbia
dc.subjectCanada
dc.subjectgold ores
dc.subjectmetal ores
dc.subjectoxides
dc.subjectmineral exploration
dc.subjectsediments
dc.subjectcopper ores
dc.subjectmagnetite
dc.subjecttill
dc.subjectclastic sediments
dc.subjectWestern Canada
dc.subject.departmentSchool of Earth and Ocean Sciences
dc.subject.departmentDepartment of Biology
dc.titleMagnetite as an Indicator Mineral in the Exploration of Porphyry Deposits: A Case Study in Till near the Mount Polley Cu-Au Deposit, British Columbia, Canadaen_US
dc.typePostprinten_US

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