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TitleMagmatic evolution of the Late Devonian Mount Douglas leucogranites, southwestern New Brunswick, Canada; an example of extreme fractional crystallization
LicencePlease note the adoption of the Open Government Licence - Canada supersedes any previous licences.
AuthorMohammadi, N; Lentz, D R
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. 547-557, Open Access logo Open Access
LinksCanadian Database of Geochemical Surveys, downloadable files
LinksBanque de données de levés géochimiques du Canada, fichiers téléchargeables
PublisherNatural Resources Canada
Documentopen file
Mediaon-line; digital
RelatedThis publication is contained in TGI 4 - Intrusion Related Mineralisation Project: new vectors to buried porphyry-style mineralisation
File formatpdf
ProvinceNew Brunswick
AreaMount Douglas
Lat/Long WENS -68.0000 -66.5000 46.0000 45.0000
Subjectseconomic geology; tectonics; mineralogy; porphyry deposits; porphyry copper; mineral exploration; mineralization; biotite; granodiorites; leucogranites; hydrothermal deposits; hydrothermal alteration; tungsten; molybdenum; gold; antimony; magmatic rocks; tectonic environments; tectonic setting; tectonic evolution; granophile deposits; mass spectrometer analysis; magmatic deposits; magmatism; Paleozoic; Devonian
Illustrationslocation maps; plots; photomicrographs; ternary diagrams
ProgramTargeted Geoscience Initiative (TGI-4) Intrusion/Porphyry Ore Systems
Released2015 06 11; 2023 03 17
AbstractThe Late Devonian Mount Douglas intrusive suite (MD, ~600 km2) of southwestern New Brunswick, Canada, eastern part of the Saint George Batholith, is a suite of peraluminous leucogranites extended from Red Rock Lake to Mount Douglas. Extreme fractional crystallization associated with formation of this suite is the most important factor affecting the magmatic evolution, producing three compositionally and chronologically different intrusive units, Dmd1, Dmd2, and Dmd3. Petrochemical data show that the subunits of the Mount Douglas Granite have within-plate geochemical character with evidence of hybrid I- and S-type affinity.
Very low K/Rb (average 102.7), Nb/Ta (? 6.8), and Zr/Hf (? 37.45) ratios in Dmd3 compared to Dmd1 possibly reflect significant involvement of extreme low T crystal fractionation in the last- stages of magmatic differentiation; The continuous variation trends for many major and trace elements (e.g., Zr vs. TiO2, Zr/Hf vs. K/Rb, F vs. K/Rb, and Pb vs. Ba) suggest that probably Dmd2 and Dmd3 were generated by extensive fractionation of the parental Dmd1 magma. Also, normalized to the least-evolved sample of the MG granites (Dmd1), the Dmd3 unit is the most enriched in Rb, Th, U, Ce, Ta, Pb, Nd, Sm, Dy, Y, Yb, and Lu, and depletion of Cs, Ba, Sr, P, Zr, Eu, and Ti content, reflects their production of the same parental magma by crystal fractionation from Dmd1 to Dmd3. A flat "birdwing shape" REE patterns with the most pronounced negative Eu anomalies and the lowest (La/Yb)N (ranging from 1.7-7.4) ratios of Dmd3 show the highly evolved attributes of Dmd3. Calculation of zircon saturation temperatures supports an interpretation of crystal fractionation from Dmd1 to Dmd3. Estimated average temperatures using the bulk rock Zr composition for Dmd1, Dmd2, and Dmd3 range 747-826°C, 733-817°C, and 729-816°C, respectively. All above data suggest that they might have a single genetic group with different fractionation originated from a homogenous parental magma, in which this fractionation increases from the early unit (Dmd1) to the latest unit (Dmd3); significant mineral occurrences, such as Sn, W, and Mo, seem to be mostly associated with the latest and most highly differentiated Dmd3 intrusive phases.
Summary(Plain Language Summary, not published)
The Targeted Geoscience Initiative (TGI-4) is a collaborative federal geoscience program that provides industry with the next generation of geoscience knowledge and innovative techniques to better detect buried mineral deposits, thereby reducing some of the risks of exploration. This volume summarises research activities completed under the TGI 4 Intrusion Related Mineralisation Project that focused on porphyry-style ore systems related to the Cu- and Cu-Mo deposits of South-Central British Columbia and the Sn-W-Mo-In deposits in New Brunswick, Nova Scotia and Newfoundland.

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