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TitreUsing biotite composition of the Devonian Lake George granodiorite, New Brunswick, as a case study for 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. 459-474, (Accès ouvert)
LiensCanadian Database of Geochemical Surveys, downloadable files
LiensBanque de données de levés géochimiques du Canada, fichiers téléchargeables
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
Référence reliéeCette publication est reliée les publications suivantes
Lat/Long OENS -68.0000 -66.5000 46.0000 45.0000
Sujetsgisements porphyriques; cuivre porphyrique; prospection minière; minéralisation; biotite; granodiorites; gisements minéraux hydrothermaux; altération hydrothermale; tungstène; molybdène; or; antimoine; roches magmatiques; Dépôt de Mount Pleasant ; géologie économique; pétrologie ignée et métamorphique; Paléozoïque; Dévonien
Illustrationslocation maps; photomicrographs; ternary diagrams; plots; photographs; tables
ProgrammeInitiative géoscientifique ciblée (IGC-4), Étude des gîtes porphyriques
Diffusé2015 06 11
Résumé(disponible en anglais seulement)
The granodioritic Lake George polymetallic deposit is located approximately 35 km southwest of Fredericton, New Brunswick. This intrusion is a metaluminous to weakly peraluminous, calc-alkaline body that shows an evolved I-type, volcanic arc affinity. Based on an Early Devonian age determination, (412 +5/-4 Ma, zircon U-Pb) it is related to the Hakshaw granite phase of the Pokiok Batholith. The Lake George stock is cut by Hibbard stibnite -quartz veins and quartz-scheelite-molybdenite veinlets that contain significant amounts of gold. Fresh biotites from this intrusion were analyzed at both the core and rim by electron microprobe, and along rim to rim transects by laser ablation ICP-MS at the University of New Brunswick to build an understanding of the halogens responsible for mineralization and trace element distribution within this deposit.
Biotites of this intrusion are reddish brown in colour (indicative of reduced I-type source) and mostly altered to chlorite. They usually contain apatite, zircon, titanite, ilmenite, rutile, and sulphide minerals as mineral inclusions. Temperature was calculated with the Ti-In-biotite geothermometer, in which the results showed a variation between 583 and 745°C.
Two depths of emplacement were determined based on the Al in hornblende and biotite geobarometries confirming the porphyritic texture of this intrusion (4.3 and 1.5 km, respectively). Forming amphiboles at that depth clearly indicates a high water content of the source magma; in addition, hydroxyl is the most dominant component of the hydroxyl site (Average 1.89 wt%) in biotites. The limited range of IV(F/Cl) values of the Lake George biotites suggested that they all equilibrated with one fluid.
Even though there is no noticeable difference in major elements from core to rims, evidence of magma evolution is recorded by biotite grains by their trace elements. For instance, Cu, Rb, Cr, K, Mo, Sn, Cs and W increase from core to rims, whereas Ba, Ni, Mn, and Li act inversely. Sb has a negligible variation from core to rim. Interestingly, the partition coefficient (biotite/whole-rock) is significantly small for Sb, W, and Mo (main associated mineralization) with 0.06, 0.28 and 0.13 in pure magmatic biotites and increase to 0.77, 1.93 and 0.20 in more altered biotites reflecting enrichment of these elements towards the late stage fluid.
Based on these observations, the concept of using mica composition to help identify fertile Acadian magma systems was proved; this method may be a useful tool to indicate the difference between barren and mineralized granophileelement rich systems.