Spatio-temporal distribution of Devonian post-accretionary granitoids in the Canadian Appalachians: implications for tectonic controls on intrusion-related mineralization

Kellett, Dawn A.; Piette-Lauzière, Nicolas; Mohammadi, Nadia; Bickerton, Luke; Kontak, D. J.; Rogers, N; Larson, Kyle P.

doi:10.4095/327955

Cited by 5 publications

(2 citation statements)

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“…In the northern Appalachians, the temporal and spatial distribution of granitoids and related mineralization are controlled by the tectonic history of the orogen, specifically the regional to local structural features (Kellett et al, 2021). According to Ruitenberg et al (1977) and Ruitenberg and Fyffe (1982), Acadian and post-Acadian mineral deposits in southern NB are correlated with a distinct sequence of tectonic events with a significant variety of epigenetic deposits occurring in and along the contacts of Middle Devonian to Early Carboniferous igneous intrusions and associated subvolcanic stocks emplaced in extension structures.…”

Section: Geological Settingmentioning

confidence: 99%

Zircon compositional systematics from Devonian oxidized I-type granitoids: examination of porphyry Cu fertility indices in the New Brunswick Appalachians, Canada

Yousefi,

Lentz,

McFarlane

et al. 2024

Front. Earth Sci.

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Zircon is a common, widely distributed accessory mineral in most igneous rocks and its refractory nature records magmatic evolution in terms of oxygen and U-Th-Pb isotopes, and trace-element contents all of which reflect the intrinsic physio-chemical evolution of the magmatic systems in which it crystallized. Zircon compositions can be used as an indicator of relative fertility of hypabyssal intrusions in terms Cu ± Mo ± Au porphyry mineralization. To further characterize syn- to post-collisional adakitic Devonian oxidized I-type granitoids in the New Brunswick (specifically, those with Cu ± Mo ± Au porphyry-style mineralization), LA-ICP-MS analyses (guided by µXRF-EDS mapping and SEM-BSE imaging of polished thin sections) of zircons from 13 granitoids was conducted. The zircons studied were similar in terms of their textures (homogenous cores, patchy zoning, oscillatory zoning, and some unzoned zircon); however, they have a wide range of trace- and minor-element (Hf, HREE, Y, Th, U) compositions. Specifically, Zr/Hf ranges between 24–60, whereas Th/U ranges between 0.15 and 5.37. The presence of inherited zircon affects the concentrations of Th and U, as well as other key elements. Estimated crystallization temperatures of granitoids, ranging from 737 to 899°C, were calculated via Ti-in-zircon geothermometry assuming reduced TiO2 and SiO2 activities. The calculated log fO2 values for zircons from some of these granitoids indicate a highly oxidized magmatic signature. Zr/Hf, Eu/Eu⁎, and (Eu/Eu⁎)/Y in zircon, as well as zircon (Ce/Nd)/Y are some of the best indicators of porphyry fertility. The Ce/Ce* in zircon exhibit a large range (1.1–590), with higher Ce/Ce* reflecting more metallogenically favourable oxidizing conditions. If Eu/Eu⁎ in zircon is ≥0.4 (relatively oxidized conditions), it indicates a high potential for an ore-forming porphyry Cu mineralizing system. Lower Eu contents reflect relatively reducing conditions, as Eu anomalies vary with oxygen fugacity as well, and the relative abundance of Eu2+ is higher, but does not substitute into the zircon lattice. The evidence extracted from analyzing the zircon composition within New Brunswick’s I-type granitoids indicates the fertility of these hypabyssal intrusions.

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Section: Geological Settingmentioning

confidence: 99%

Zircon compositional systematics from Devonian oxidized I-type granitoids: examination of porphyry Cu fertility indices in the New Brunswick Appalachians, Canada

Yousefi,

Lentz,

McFarlane

et al. 2024

Front. Earth Sci.

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“…reflect subduction-related processes, followed by slabbreakoff and mantle upwelling (e.g., van Staal et al 2009van Staal et al , 2021Wilson et al 2017;Kellett et al 2021).…”

Section: Assembly and Evolution Of The Smbmentioning

confidence: 99%

The age and origin of the South Mountain Batholith (Nova Scotia, Canada) as constrained by zircon U–Pb geochronology, geochemistry, and O–Hf isotopes

et al. 2022

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The South Mountain Batholith (SMB; Nova Scotia, Canada) is the largest composite batholith exposed in the Appalachians and lies entirely within the most outboard Meguma terrane. In-situ and CA-TIMS U-Pb dating and in-situ isotopes (Lu-Hf, O) and geochemistry for zircon from all phases of the SMB constrain its source as well as its evolution. CA-ID-TIMS for zircon yield emplacement (autocryst) ages indicating a transition from granodiorite (378.7 ± 1.2 to 375.4 ± 0.8 Ma) to leucogranite (375.4 to 371.8 ± 0.8 Ma) over several million years. Furthermore, in situ SHRIMP, LA-MC-ICP-MS, and SIMS analyses of distinct zircon domains reveal: 1) abundant ancient xenocrysts (~420 Ma to 2.2 Ga); 2) antecryst ages ca. 3–15 million years older than SMB emplacement; 3) autocryst δ18O values between +7.3 and +9.1‰ (V-SMOW); 4) similar isotopes, REE signatures, and derived fO2 values among antecrysts and autocrysts; and 5) εHf values from the 371.8 ± 0.8 Ma Davis Lake Pluton (DLP) autocrysts that are higher (+1.74 to +4.38) than the rest of the SMB (-2.99 to +1.68). Collectively, these data suggest a protracted magmatic evolution for the SMB with melt generation and assembly from ~390 to 370 Ma via melting of a metasomatized mantle source followed by contamination, first from the structurally underlying Avalonian terrane and later by metasedimentary wall rocks of the Meguma terrane. The most southwesterly part of the SMB (i.e., DLP) represents a petrogenetically distinct magmatic phase that underwent less overall contamination than the rest of the SMB.

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Crustal melting recorded by dykes along the gold-bearing Melanson Brook Fault, northern New Brunswick Appalachians

Bustard,

Lentz,

Walker

et al. 2024

Can. J. Earth Sci.

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Dykes intruding along the Melanson Brook Fault record two magmatic episodes in northern New Brunswick. Dykes at the South Gold Zone of the Elmtree gold deposit are aphanitic and magnesian-calcic, whereas those at Ellis Brook (2.5 km to the west) are ilmenite-series and weakly peraluminous with hornblende- and plagioclase-porphyritic phases. Elevated 147Sm/44Nd generated by partial melting, titanium depletion, absence of rare earth element fractionation, and trondhjemite-like compositions indicate the South Gold Zone dykes were sourced from low-volume fluid fluxed melting of gabbroic crust. A Sm-Nd depleted model mantle age of 1.1 Ga for the Ellis Brook dykes suggests that they were sourced from melting of Ganderian crustal rocks rather than the sinking Acadian slab. 143Nd/144Nd evolution curves for the South Gold Zone dykes intersect that of the Ellis Brook dykes at 432 Ma and 427 Ma. This suggests that the magma from which the South Gold Zone dykes crystallized was extracted from a similar source area as the magma that generated the Ellis Brook dykes. Evidence of fluid exsolution in the Ellis Brook dykes indicates they could be a potential source for reduced intrusion-related gold mineralization. The Ellis Brook dykes yielded a U-Pb zircon age of 391 ± 5 Ma, which is consistent with the timing of oceanic slab break-off at the end of the Acadian orogenic cycle. Extraction of South Gold Zone magma occurred up to 40 Myr earlier, likely during the Salinic orogenic cycle.

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Spatio-temporal distribution of Devonian post-accretionary granitoids in the Canadian Appalachians: implications for tectonic controls on intrusion-related mineralization

Cited by 5 publications

References 0 publications

Zircon compositional systematics from Devonian oxidized I-type granitoids: examination of porphyry Cu fertility indices in the New Brunswick Appalachians, Canada

Zircon compositional systematics from Devonian oxidized I-type granitoids: examination of porphyry Cu fertility indices in the New Brunswick Appalachians, Canada

The age and origin of the South Mountain Batholith (Nova Scotia, Canada) as constrained by zircon U–Pb geochronology, geochemistry, and O–Hf isotopes

Crustal melting recorded by dykes along the gold-bearing Melanson Brook Fault, northern New Brunswick Appalachians

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