SELENIUM AND SULFUR CONCENTRATIONS IN COUNTRY ROCKS FROM THE DULUTH COMPLEX, MINNESOTA, USA: IMPLICATIONS FOR FORMATION OF THE Cu-Ni-PGE SULFIDES

Queffurus, Matthias; Barnes, Sarah‐Jane

doi:10.2113/econgeo.109.3.785

Cited by 21 publications

(16 citation statements)

References 21 publications

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“…The AFC and SFC rock sequences of our simulations (Fig. 7) are compatible with the previous suggestions that the noritic rocks of the Partridge River intrusion in the Duluth Complex formed by assimilation of the Virginia Formation black shale (e.g., Thériault and Barnes, 1998;Ripley et al, 2007;Queffurus and Barnes, 2014;Samalens et al, 2017). In the presented AFC scenario, more norite is produced relative to the SFC scenarios (Fig.…”

Section: Implications For the Origin Of The Major Rock Types Of The D...supporting

confidence: 90%

“…For instance, the natural cumulate stratigraphies have mostly been constructed by visual estimates of modal mineral compositions in hand samples, which are susceptible to inaccuracies, as pointed out by Severson et al (1996). In addition, the natural cumulates are regionally variable and include olivine gabbro and gabbro, which are absent in the reference stratigraphy but which have been reported from the Troctolitic Series in the Partridge River intrusion by many studies (e.g., Rao and Ripley, 1983;Miller and Ripley, 1996;Ripley et al, 2007;Queffurus and Barnes, 2014). Such gabbros are compatible with our FC simulations.…”

Section: Implications For the Origin Of The Major Rock Types Of The D...supporting

confidence: 88%

“…1), named after their characteristic rock types (e.g., Miller et al, 2002). A variety of ultramafic, gabbroic, and noritic rocks are also present, and locally dominant, in both the Anorthositic and Troctolitic Series intrusions (e.g., Rao and Ripley, 1983;Miller and Ripley, 1996;Miller et al, 2002;Ripley et al, 2007;Queffurus and Barnes, 2014). Pegmatitic troctolites are also present locally (Severson and Barnes, 1991;Ripley et al, 1993;Severson et al, 1996).…”

Section: Igneous Rocks and Sulfide Depositsmentioning

confidence: 99%

“…Norites are volumetrically minor, and they are mainly present along the contacts to the Virginia Formation black shale footwall and xenoliths (Rao and Ripley, 1983;Thériault and Barnes, 1998;Ripley et al, 2007;Queffurus and Barnes, 2014;Samalens et al, 2017). The presence of black shale footwall and xenoliths with restitic minerals and recrystallized partial melt has been taken as evidence that the norites formed when the Duluth Complex parental melt assimilated black shale partial melts (Ripley and Alawi, 1986;Thériault and Barnes, 1998;Queffurus and Barnes, 2014;Samalens et al, 2017). The absence of sharp compositional gradients around the restitic xenoliths implies that the partial melt assimilation occurred when the magma was mostly molten and widespread chemical mixing was possible (Ripley and Alawi, 1986).…”

Section: Igneous Rocks and Sulfide Depositsmentioning

confidence: 99%

“…The selective nature of sulfur assimilation is evident as Sr, Pb, and Nd isotope composition of the troctolites constrains bulk assimilation to ≤5 wt %, which cannot explain the sulfur mass balance (Grant and Molling, 1981;Ripley et al, 1999b). The norite-hosted deposits with disseminated and massive sulfides show evidence of more extensive assimilation, and they likely formed by the introduction of sulfides via silicate partial melts from Virginia Formation xenoliths (Thériault and Barnes, 1998;Queffurus and Barnes, 2014;Samalens et al, 2017). Radiogenic isotopic data of the norites is scarce compared to the troctolites, but oxygen isotopes indicate that black shale assimilation is generally more than 20 wt % (Ripley et al, 2007).…”

Section: Igneous Rocks and Sulfide Depositsmentioning

confidence: 99%

See 4 more Smart Citations

Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator

Virtanen¹,

Heinonen²,

Barber³

et al. 2021

Preprint

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The timing and degree of immiscible sulfide precipitation in a magma effectively controls the formation of magmatic sulfide deposits and the budget of degassing sulfur species in volcanic systems. Besides the absolute sulfur (S) content, sulfide precipitation is strongly affected by the sulfur content at sulfide saturation (SCSS) in the host silicate melt. Assimilation of S-rich wall-rocks, such as black shales, effectively increases the S content in the magma, while simultaneously lowering the SCSS. Accordingly, assimilation has been identified as the most important process in the formation of many economically significant magmatic base metal sulfide deposit, especially in continental tectonic settings. Detailed understanding of the relation between wall-rock assimilation and sulfide saturation requires accurate thermodynamic models for open magmatic systems experiencing assimilation-fractional crystallization (AFC).The Magma Chamber Simulator (MCS) is currently the only geochemical modeling software that considers the thermodynamic phase equilibria in open magmatic systems involving magma and wall-rock (and recharge) subsystems. We utilized the MCS to explore how assimilation affects the SCSS and S content of the magma. With the current lack of thermodynamic data for sulfides, we tentatively modeled S as a trace element and varied its compatibility to wall-rock in the different models. For a case study, we chose the mafic layered intrusions of Duluth Complex, Minnesota, which host some of the largest Cu-Ni sulfide deposits in the world. Assimilation of the adjacent black shale has been established as the main source for S in the deposits.Our MCS models show in detail how continuous assimilation of the black shale lowers the SCSS of the melt. Partial melt from the black shale enriches the magma in SiO2, Al2O3, K2O, and H2O, while depleting FeO, MgO, CaO, and Na2O, which causes a first order decrease in the SCSS. The compositional change also replaces troctolitic cumulates (plagioclase, olivine &#177; clinopyroxene) with norite (plagioclase and orthopyroxene), which leads to more pronounced FeO depletion in the melt, further lowering the SCSS. On the other hand, the assimilated partial melt also increases the melt mass in the magma subsystem, which counteracts the S enrichment. Accordingly, in the model where S is compatible to the wall-rock residual, the degree of sulfide saturation only slightly increases relative to the same magma experiencing FC without assimilation.More than half of the wall-rock S must partition to the assimilated partial melt in order to meet the S isotopic criteria of the modeled Cu-Ni-deposits. The main stage of sulfide precipitation is associated with ~30 wt.% crystallization of the assimilating host magma. The proportion of sulfides relative to silicates in these models is smaller than observed in the Duluth Complex deposits, which underlines the role of dynamic processes in concentrating sulfides from the silicate magma.

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Section: Implications For the Origin Of The Major Rock Types Of The D...supporting

confidence: 90%

Section: Implications For the Origin Of The Major Rock Types Of The D...supporting

confidence: 88%

Section: Igneous Rocks and Sulfide Depositsmentioning

confidence: 99%

Section: Igneous Rocks and Sulfide Depositsmentioning

confidence: 99%

Section: Igneous Rocks and Sulfide Depositsmentioning

confidence: 99%

See 3 more Smart Citations

Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator

Virtanen¹,

Heinonen²,

Barber³

et al. 2021

Preprint

View full text Add to dashboard Cite

show abstract

An overview of chalcophile element contents of pyrrhotite, pentlandite, chalcopyrite, and pyrite from magmatic Ni-Cu-PGE sulfide deposits

2020

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Sedimentary and metamorphic processes priming black shale for magmatic assimilation of sulfur: an example from the Virginia Formation, Minnesota, United States

Virtanen,

Heinonen,

Märki

et al. 2024

Miner Deposita

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The copper-nickel(-platinum-group element) sulfide resources of the Duluth Complex, Minnesota, USA, formed by assimilation of sulfur from the Virginia Formation black shale. In the normal black shale of the Virginia Formation, sulfur is mainly hosted in disseminated pyrite, whereas mm-scale pyrrhotite laminae dominate in the sulfur-rich Bedded Pyrrhotite Unit. The Bedded Pyrrhotite Unit was the main supply of sulfur in some of the magmatic sulfide deposits but its origin has not been studied in detail. Using Raman spectroscopy, we show that the carbonaceous material within the regionally metamorphosed normal black shale is graphitized biogenic material. The Bedded Pyrrhotite Unit contains pyrobitumen that represents residues of oil that accumulated to porous horizons, which formed due to dissolution of precursor sedimentary clasts. Replacement of the clasts by quartz and sulfides facilitated the formation of the pyrrhotite laminae of the Bedded Pyrrhotite Unit, which likely occurred during regional metamorphism.The pyrite-bearing normal black shale experienced loss of H2O, Corg, and sulfur during devolatilization caused by the Duluth Complex. The contact-metamorphosed Bedded Pyrrhotite Unit shows no systematic depletion of volatiles and is the most Corg and sulfur-rich part of the Virginia Formation. During devolatilization, sulfur was preserved because unlike pyrite, pyrrhotite was stable. Consequently, magmatic assimilation of sulfur from the Bedded Pyrrhotite Unit required partial melting. Retrograde hydration introduced H2O, and possibly Corg, and sulfur, to the contact-metamorphosed Bedded Pyrrhotite Unit, which further affected the volatile budget. Our findings highlight why constraining diagenetic and regional metamorphic processes is important to understand magma-sediment interaction processes.

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SELENIUM AND SULFUR CONCENTRATIONS IN COUNTRY ROCKS FROM THE DULUTH COMPLEX, MINNESOTA, USA: IMPLICATIONS FOR FORMATION OF THE Cu-Ni-PGE SULFIDES

Cited by 21 publications

References 21 publications

Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator

Modeling the sulfide saturation in continuously assimilating magmatic systems with the Magma Chamber Simulator

An overview of chalcophile element contents of pyrrhotite, pentlandite, chalcopyrite, and pyrite from magmatic Ni-Cu-PGE sulfide deposits

Sedimentary and metamorphic processes priming black shale for magmatic assimilation of sulfur: an example from the Virginia Formation, Minnesota, United States

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