Copper isotope evidence for large-scale sulphide fractionation during Earth’s differentiation

Savage, Paul S.; Moynier, Frédéric; Chen, H.; Shofner, Gregory A.; Siebert, J.; Badro, James; Puchtel, I. S.

doi:10.7185/geochemlet.1506

Cited by 160 publications

(201 citation statements)

References 25 publications

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“…A reasonable explanation for the Cu isotope discrepancy between the BSE and chondrites replies on Cu isotope fractionation during iron-sulfide/silicate segregation during core formation and core-mantle interaction. A recent study proposed that the heavier Cu isotopic composition of the BSE than the chondritic bulk Earth may result from preferential partitioning of light Cu isotopes into sulphide during core formation (Savage et al, 2015). This evokes the potential using Cu isotopes to understand the core-mantle differentiation process.…”

Section: Cu Isotopic Composition Of the Bse And Comparison With Othermentioning

confidence: 98%

“…The stable isotope system of Cu may hold the potential to constrain the crust-mantle differentiation and mantle-core differentiation processes that involve Cu partitioning between sulfides and silicates (Savage et al, 2015). For these applications the Cu isotopic compositions of the silicate Earth's reservoirs and possible Cu isotope fractionation during mantle partial melting, slab fluid enrichment and magmatic differentiation need to be constrained.…”

Section: Introductionmentioning

confidence: 99%

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Copper isotopic composition of the silicate Earth

Liu

Huang

Liu

et al. 2015

Earth and Planetary Science Letters

151

183

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Section: Cu Isotopic Composition Of the Bse And Comparison With Othermentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Copper isotopic composition of the silicate Earth

Liu

Huang

Liu

et al. 2015

Earth and Planetary Science Letters

151

183

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“…Ikehata and Hirata [58] suggested the range of terrestrial magmatic copper is −0.27‰ to 0.27‰. In general, the δ 65 Cu of terrestrial basalt is~0‰ [4,54,59]. The δ 65 Cu bulk silicate Earth is estimated to be +0.06 ± 0.20, and thus, fractionation during partial melting is limited [54].…”

Section: Initial δ 65 Cu Composition Of Source Rocksmentioning

confidence: 99%

Copper Isotope Constraints on the Genesis of the Keweenaw Peninsula Native Copper District, Michigan, USA

Bornhorst

Mathur

2017

Minerals

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Abstract:The Keweenaw Peninsula native copper district of Michigan, USA is the largest concentration of native copper in the world. The copper isotopic composition of native copper was measured from stratabound and vein deposits, hosted by multiple rift-filling basalt-dominated stratigraphic horizons over 110 km of strike length. The δ 65 Cu of the native copper has an overall mean of +0.28‰ and a range of −0.32‰ to +0.80‰ (excluding one anomalous value). The data appear to be normally distributed and unimodal with no substantial differences between the native copper isotopic composition from the wide spread of deposits studied here. This suggests a common regional and relatively uniform process of derivation and precipitation of the copper in these deposits. Several published studies indicate that the ore-forming hydrothermal fluids carried copper as Cu 1+ , which is reduced to Cu 0 during the precipitation of native copper. The δ 65 Cu of copper in the ore-forming fluids is thereby constrained to +0.80‰ or higher in order to yield the measured native copper values by reductive precipitation. The currently accepted hypothesis for the genesis of native copper relies on the leaching of copper from the rift-filling basalt-dominated stratigraphic section at a depth below the deposits during burial metamorphism. Oxidative dissolution of copper from magmatic source rocks with magmatic δ 65 Cu of 0‰ ± 0.3‰ is needed to obtain the copper isotopic composition of the metamorphogenic ore-forming hydrothermal fluids. In order to accommodate oxidative dissolution of copper from the rift-filling basalt source rocks, the copper needs to have been sited in native copper. Magmatic native copper in basalt is likely stable when the magma is low in sulfur. Low sulfur is predicted by the lack of sulfide minerals in the ore deposits and in the rift-filling basalt-dominated section, which are source rocks, the same rocks through which the ore fluids moved upwards, and the host rocks for the native copper ores. When combined with geologic evidence and inferences, the copper isotopic composition of native copper helps to further constrain the genetic model for this unique mining district.

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“…A series of metal-silicate experiments 664 performed by Savage et al (2015b) indicated that the heavier Cu isotope prefers to enter 665 the metal phase. This would suggest (given that 2/3 of Earth's Cu is in the core) that bulk 666…”

Section: Cu Contents Do Not Plot On Olivine Control Lines (Savage Et mentioning

confidence: 99%

“…It could be that impact-driven volatilization created this depletion, 673 which would preferentially lead to the loss of light Cu, leaving a heavy residue. suggests that, if such a reservoir formed and eventually was admixed into the 694 core (it would sink through the mantle due to its higher density), it could add 695 up to ~0.8wt.% S to the core (Savage et al 2015b). 696…”

Section: Cu Contents Do Not Plot On Olivine Control Lines (Savage Et mentioning

confidence: 99%