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TitreMineral chemistry of greenrock alteration associated with the porphyry Cu-Mo mineralization at the Gibraltar deposit, south central British Columbia, Canada
AuteurKobylinski, C H; Hattori, K; Plouffe, A; Smith, S
SourceWhitehorse 2016, Geological Association of Canada, Mineralogical Association of Canada, abstracts; 2016 p. 1
Année2016
Séries alt.Secteur des sciences de la Terre, Contribution externe 20150489
ÉditeurAssociation géologique du Canada
Documentpublication en série
Lang.anglais
Mediaen ligne; numérique
Formatspdf
ProvinceColombie-Britannique
Sujetsaltération; minéralisation; cuivre; molybdène; gisements porphyriques; épidote; chloritisation; métamorphisme; pétrologie ignée et métamorphique; Trias
ProgrammeÉtude des gîtes porphyriques, Initiative géoscientifique ciblée (IGC-4)
LiensOnline - En ligne
Résumé(disponible en anglais seulement)
The Gibraltar Cu-Mo porphyry deposit with the geological reserves (past production plus reserves) of 2.8 Mt Cu is hosted by in the late Triassic Granite Mountain batholith of late Triassic age in the Quesnellia tTerrane. The batholith, which has the surface exposure of 15 km x 10 km, is mostly composed of tonalite with minor variation in modal abundances of felsic and mafic minerals. Igneous minerals are plagioclase, quartz, biotite, hornblende, with minor amounts of titanite, zircon, apatite and magnetite. Bulk rocks show a typical subduction-related geochemical signature with negative anomalies of high field strength elements, such as Nb, Ta and Ti, with minor positive and negative Eu anomalies (Eu/Eu*=0.09-1.2). The mineralization is accompanied by extensive alteration in the tonalite, which produced illite, quartz, rutile, titanite, magnetite, apatite, chlorite and epidote. The high-temperature potassic alteration zone was likely present in the centre of the current mining operation, but the alteration has been obscured by the replacement of secondary biotite by chlorite. Among alteration minerals, epidote and chlorite are ubiquitous in the tonalitic rocks in and around the mine, producing green rock alteration. Epidote group minerals primarily replace plagioclase. Chlorite is also common after hornblende and biotite, and a mixture of titanite and rutile replaces biotite and hornblende. Epidote minerals are light grass green in hand specimens and also thin sections. They show a large compositional variation even within one sample from Al-rich (high clinozoisite component) to Fe-rich epidote, suggesting multiple alteration events or reflecting varying fluid composition within a hydrothermal system. Some are yellowish in thin sections and they contain significant allanite component with high La2O3 (up 9.54 wt%) and Ce2O3 (up to 14.7 wt%). These Ce-La-rich epidote grains contain higher concentrations of other REEs, Mn, Y and Th than Fe-rich epidote. These LREE-rich epidotes form isolated grains within chlorite aggregates in epidote-rich tonalities. In contrast, Fe-rich, REE-poor epidote is abundant and preferentially replaces plagioclase. Igneous titanite (up to 2 mm) is low in Al2O3 (~1.2 wt%) whereas hydrothermal titanite contains high Al2O3 ranging from 2 to 6 wt%. Hydrothermal titanite is more abundant than its igneous counterpart, and shows a wide compositional variation of Mg and Fe. Rocks with greenrock alteration show high abundances of U, Pb and K in bulk rocks compared to epidote-poor samples. The enrichment of U and Pb in bulk rocks is likely due to their incorporation in epidote as minor components.
Résumé(Résumé en langage clair et simple, non publié)
La composition de minéraux spécifiques d'une roche en place riche en cuivre et molybdène a été determinée dans le but d'identifier les mêmes minéraux avec la même composition dans les sédiments glaciaires. En d'autres mots, certains minéraux dans les sediments ayant une composition spécifique peuvent être reliés à une source précise dans la roche en place riche en cuivre et molybdène. Les résultats de ces travaux ont une implication directe pour la prospection minérale.
GEOSCAN ID297848