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TitleHigh cerium anomalies in zircon from intrusions associated with porphyry copper mineralization in the Gibraltar deposit, south-central British Columbia
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AuthorKobylinski, C H; Hattori, K; Smith, S W; Plouffe, A
SourceGeological Survey of Canada, Open File 8430, 2018, 19 pages, https://doi.org/10.4095/311194
Year2018
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
File formatreadme
File formatpdf (Adobe® Reader®); rtf; xlsx (Microsoft® Excel®)
ProvinceBritish Columbia
NTS93B/07; 93B/08; 93B/09; 93B/10
AreaGibraltar
Lat/Long WENS-122.5833 -122.0833 52.6667 52.4167
Subjectseconomic geology; geochemistry; geochronology; surficial geology/geomorphology; mineral exploration; mineral deposits; porphyry deposits; copper; molybdenum; mineralization; geochemical anomalies; bedrock geology; lithology; igneous rocks; intrusive rocks; tonalites; diorites; tectonic history; intrusions; metamorphism; foliation; magmatism; alteration; oxidation; isotope ratios; uranium thorium ratios; cerium geochemistry; radiometric dating; uranium lead dating; zircon dates; cerium geochemistry; neodymium geochemistry; samarium geochemistry; glacial deposits; sediment geochemistry; stream sediment geochemistry; bulk samples; whole rock analyses; mass spectrometer analysis; trace element analyses; electron microscope analyses; Gibraltar Deposit; Quesnel Terrane; Granite Mountain Batholith; Canadian Cordillera; Sheridan Creek Stock; Highland Valley Copper Deposit; Guichon Creek Batholith; Burgess Creek Stock; neodymium-ytterbium ratios; cerium-cerium ratios; rhenium-osmium dating; rare earth element analyses; europium-europium ratios; cerium-neodymium ratios; cathodoluminescence analyses; Phanerozoic; Mesozoic; Cretaceous; Jurassic; Triassic
Illustrationsgeoscientific sketch maps; tables; photomicrographs; geochemical plots
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Location
 
Natural Resources Canada Library - Ottawa (Earth Sciences)
 
ProgramPorphyry systems, Targeted Geoscience Initiative (TGI-5)
Released2018 09 20
AbstractThe Gibraltar porphyry-Cu deposit in the Quesnel Terrane in south-central British Columbia is hosted by the Late Triassic to Early Jurassic Granite Mountain Batholith (GMB). The GMB has been classified into four phases of tonalitic rocks with minor quartz diorite. The rocks of the Mine Phase, host of the Cu mineralization, are foliated tonalite and are extensively altered to form K-feldspar, white mica, epidote and pyrite. All zircon grains examined from the GMB are magmatic with Th/U ranging from 0.15 to 1.44 and low Nd/Yb ratios below 0.01. U-Pb dating of zircons reveals three Cu-mineralized intrusions within the Mine Phase ranging from 201 to 218 Ma. The age gaps between the mineralized intrusions are larger than the uncertainty of the age data. Zircons from the oldest Cu- mineralized intrusion (218.9±3.1 Ma) in the Mine Phase record the highest Ce4+/Ce3+ (680± 180 (1 sigma), n=14). Zircons from the two other groups of Cu-mineralized intrusions in the Mine Phase show lower Ce4+/Ce3+ (214± 64 (1 sigma), n=43) and those from the unmineralized Border and Granite Mountain phases of the GMB show even lower Ce4+/Ce3+ (128± 35 (1 sigma), n=108). Zircons from the Cretaceous Sheridan Creek Stock, south of the GMB, show low Ce4+/Ce3+ (203± 60 (1 sigma), n=28). The data suggest multiple pulses of intrusions and mineralization in the Mine Phase, which is supported by Re-Os ages of molybdenite which are similar to the second and third pulses of intrusions. Ages and Ce4+/Ce3+ values for zircons from Cu-mineralized rocks in the Mine Phase are similar to the values for intrusions associated with the Highland Valley porphyry Cu deposit in the Guichon Creek Batholith. The ratios Ce/Nd and Ce/Ce* from the measured concentrations of Ce, Nd, and Sm correlate well with Ce4+/Ce3+, based on the compositions of zircon and bulk rocks. This suggests that the compositions of detrital zircons in glacial sediments and streams may be used in mineral exploration to detect intrusions with affinity to host porphyry Cu mineralization.
Summary(Plain Language Summary, not published)
We need to improve mineral exploration methods to discover the next generation of mineral deposits for the future. With this objective in mind, we have tested the composition of a mineral called zircon which occurs in intrusive rocks like granite. Certain intrusive rocks can contain copper. We demonstrate that zircon has a specific composition if the intrusion contains copper. Furthermore, we identify the presence of zircon with a positive mineralization signal in glacial sediment. Tracing the source of zircon grains with a positive mineralisation signal allows the detection of buried copper deposits.
GEOSCAN ID311194