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TitleUsing biotite composition of the Devonian Lake George granodiorite, New Brunswick, as a case study for W-Mo-Au-Sb mineralized magmatic hydrothermal systems
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AuthorAzadbakht, Z; Lentz, D R; McFarlane, C R M
SourceTGI 4 - Intrusion Related Mineralisation Project: new vectors to buried porphyry-style mineralisation; by Rogers, N (ed.); Geological Survey of Canada, Open File 7843, 2015 p. 459-474, https://doi.org/10.4095/296483 (Open Access)
LinksCanadian Database of Geochemical Surveys, downloadable files
LinksBanque de données de levés géochimiques du Canada, fichiers téléchargeables
Year2015
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
RelatedThis publication is contained in Rogers, N; (2015). TGI 4 - Intrusion Related Mineralisation Project: new vectors to buried porphyry-style mineralisation, Geological Survey of Canada, Open File 7843
RelatedThis publication is related to the following publications
File formatpdf
ProvinceNew Brunswick
NTS21G
AreaLake George
Lat/Long WENS -68.0000 -66.5000 46.0000 45.0000
Subjectseconomic geology; igneous and metamorphic petrology; porphyry deposits; porphyry copper; mineral exploration; mineralization; biotite; granodiorites; hydrothermal deposits; hydrothermal alteration; tungsten; molybdenum; gold; antimony; magmatic rocks; Sisson deposit; Mount Pleasant deposit; Paleozoic; Devonian
Illustrationslocation maps; photomicrographs; ternary diagrams; plots; photographs; tables
ProgramIntrusion/Porphyry Ore Systems, Targeted Geoscience Initiative (TGI-4)
Released2015 06 11
AbstractThe 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.
GEOSCAN ID296483