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TitreUsing biotite composition of the Devonian Mount Elizabeth Intrusive Complex, New Brunswick, as a proxy for magma fertility and differentiation in W-Mo-Au-Sb mineralized magmatic hydrothermal systems
TéléchargerTéléchargement (publication entière)
AuteurAzadbakht, Z; Lentz, D R; McFarlane, C R M
SourceTGI 4 - Intrusion Related Mineralisation Project: new vectors to buried porphyry-style mineralisation; par Rogers, N (éd.); Commission géologique du Canada, Dossier public 7843, 2015 p. 535-546,
ÉditeurRessources naturelles Canada
Documentdossier public
Mediaen ligne; numérique
Référence reliéeCette publication est contenue dans Rogers, N; (2015). TGI 4 - Intrusion Related Mineralisation Project: new vectors to buried porphyry-style mineralisation, Commission géologique du Canada, Dossier public 7843
Lat/Long OENS -68.0000 -66.0000 48.0000 47.0000
Sujetsgisements porphyriques; cuivre porphyrique; prospection minière; minéralisation; biotite; granodiorites; gisements minéraux hydrothermaux; altération hydrothermale; tungstène; molybdène; or; antimoine; roches magmatiques; géologie économique; pétrologie ignée et métamorphique; Paléozoïque; Dévonien
Illustrationslocation maps; photomicrographs; ternary diagrams; plots
Bibliothèque de Ressources naturelles Canada - Ottawa (Sciences de la Terre)
ProgrammeÉtude des gîtes porphyriques, Initiative géoscientifique ciblée (IGC-4)
LiensCanadian Database of Geochemical Surveys, downloadable files
LiensBanque de données de levés géochimiques du Canada, fichiers téléchargeables
Diffusé2015 06 11
Résumé(disponible en anglais seulement)
The Early Devonian (418 ± 1 Ma, monazite U-Pb) Mount Elizabeth intrusive complex, New Brunswick, Canada, is a multiphase metaluminous to weakly peraluminous, high K calc-alkaline body that shows within plate affinity. The complex consists of apparently contemporaneous igneous suites including a mafic suite, an eastern peraluminous granite suite and a western alkali granite suite. The eastern part comprises compositionally and texturally homogenous biotite granite, whereas the western part is mostly heterogeneous and contains five different units. The most abundant phase of the western suite is medium- to coarse-grained alkaline equigranular granite. This complex poorly exposed so that most of the available data, including inferred contact relationships, is based on geophysical data. It should be added that no mineral occurrences have been reported so far from this complex.
Fresh biotite from this intrusion was analysed from core to rim by electron microprobe, and laser ablation ICP-MS at the University of New Brunswick to test whether biotite preserves a record of magma evolution in terms of major and trace-element and halogen compositional variations. Subhedral to elongate biotite phenocrysts are less than 700 ?m long and reddish brown in colour indicative of a reduced I-type source. A calc-alkaline affinity is also suggested by biotite major element classification schemes. Biotite is locally altered to chlorite along cleavage planes, and typically contain iron oxides, monazite, ilmenite, apatite, xenotime, and zircon as mineral inclusions.
Results of electron microprobe and laser ablation ICP-MS studies indicate that biotite grains are homogenous in major elements; however, they show variation in trace elements from core to rim. The biotite grains investigated have the highest Sn, W, Sb, and Mo concentrations recorded thus far among Devonian-related granitoid intrusions of New Brunswick (130, 40, 1, 3 ppm, respectively). There is no systematic correlation between major elements including FeTot, or FeTot/Ti and any of these trace elements. To further study trace-element distribution, a biotite from each of the phases was mapped with laser-ablation ICP-MS revealing patchy Ba, Rb, and Cs zoning. These patterns are interpreted to be a result of localized hydrothermal alteration and intracrystalline volume diffusion in these biotite grains. The intracrystalline distribution of Sn, W, Mo and Sb is homogeneous. Furthermore, halogen contents analysed by EPMA indicate that hydroxyl is the dominant component of hydroxyl site followed by fluorine. It also showed that these biotites formed from strongly contaminated and reduced I-type granite.
As a result, high concentration of Sn in biotite is interpreted to be caused by crustal contamination, and lowtemperature hydrothermal processes (sub-solidus) rather than being magmatic in origin.