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TitlePetrologic and geochemical examination of the Early Devonian, Evandale porphyry Cu-Mo-(Au) deposit, southern New Brunswick: geothermobarometric analysis of petrogenesis
AuthorWhite, T; Lentz, D; McFarlane, C
SourceGeological Association of Canada-Mineralogical Association of Canada, Joint Annual Meeting, Abstracts Volume vol. 37, 2014 p. 287 Open Access logo Open Access
LinksOnline - En ligne (PDF 8.75 MB)
PublisherGeological Association of Canada
PublisherMineralogical Association of Canada
MeetingGAC-MAC Joint annual meeting; Fredericton, NB; CA; May 2014
Mediaon-line; digital
RelatedThis publication is related to Petrologic and geochemical examination of the Early Devonian, Evandale porphyry Cu-Mo-(Au) deposit, southern New Brunswick: geothermobarometric analysis of petrogenesis
File formatpdf
ProvinceNew Brunswick
AreaMascarene Basin
Lat/Long WENS -68.0000 -64.0000 46.0000 45.0000
Subjectsigneous and metamorphic petrology; geochemistry; intrusive rocks; granodiorites; petrographic analyses; mineralization; petrogenesis; porphyry deposits; copper; molybdenum; gold; geobarometry; geothermometry; geochemical analyses; Evandale Granodiorite; Devonian
ProgramTargeted Geoscience Initiative (TGI-4) Intrusion/Porphyry Ore Systems
Released2014 01 01
AbstractPorphyry Cu-Mo-(Au) systems associated with the granitoid rocks in eastern North American orogenic belts have been researched using current deposit models; however, relatively few studies have examined the potential for late stage fine-grained porphyritic to aplitic intrusive phases being host to mineralization. The Evandale Granodiorite is an example of a well-preserved Mid-Devonian (U-Pb zircon age of 391.2 ± 3.2 Ma for the coarser granitoid, and 390.2 ± 1.6 Ma for the aplite) polyphase pluton intruding through deformed Silurian sedimentary and mafic volcanic rocks of the Mascarene Basin in southern New Brunswick. The two intrusive phases have been identified as I type granites with a minor sedimentary component. The pluton is separated both petrochemically and texturally into two distinct phases. The coarser phase ranges from medium- to coarse-grained seriate to porphyritic granodiorite to monzogranite and the later finer stage layered aplite ranges from a monzogranite to syeno-granite. INAA analysis of each phase found that the highest concentrations of Cu and Au (108 ppm Cu, and 33 ppb Au) are associated with pyrite, chalcopyrite, and arsenopyrite within the aplitic dykes sampled, whereas concentrations of up to 6 ppm Mo were detected within the c.g. granite. Current models suggest that the transport of metals (particularly Cu and Au) are sourced from secondary two-phase fluids at shallow depths (approximately 2 kb), and is controlled primarily by Cl fugacity of the magma. Analyses of biotite phenocrysts from both the aplite and granite contain an average of 0.21 wt% Cl, which is similar to other high grade Cu-Mo-(Au) porphyry deposits. Average zircon saturation temperatures were calculated to be 818°C for the aplite and 787°C for the granitoid. Average apatite saturation temperatures were found to be 880°C for the aplite and 934°C for the granitoid phase. Hornblende-plagioclase thermometry revealed the crystallization temperature of the granite to be 642°C and 600°C for the aplite, cooler than most deposits of the same type. Al in hornblende geobarometery indicates crystallization depths of ~2.1 kb for hornblende in the aplite and ~0.7 kb for the c.g. granite. The aplitic dykes were subject to higher crystallization pressures and lower crystallization temperatures suggesting that their formation may either be a result of pressure quenching of the melt during rapid ascent or by the sub-solidus recrystallization of the melt as pyroclastic flows.

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