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Copper and Other Metallic Isotope Systems
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Copper and Other Metallic Isotope Systems

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Geochemistry and Geochronology".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 26556

Special Issue Editors

Dr. Dan Asael

E-Mail Website
Guest Editor
Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA
Interests: stable isotopes; non-traditional stable isotopes; isotopic systems; sedimentary geological systems
Dr. Leslie Robbins

E-Mail Website
Guest Editor
Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA
Interests: trace metals; evolution; chemical sediments; banded iron formations; stable isotopes

Special Issue Information

Dear Colleagues,

The field of metal isotope geochemistry has attracted great attention over the last two decades, and has benefited immensely from the introduction of MC-ICP-MS instruments. This advancement in instrumentation has finally brought the accurate and precise measurement of several novel isotope systems within our reach. As a result, studies that have leveraged metallic isotope systems (including Cu, Ni, Zn, Fe, Cr, and Mo) have made valuable contributions to our understanding of Earth systems and surface processes.

In this Special Issue we aim to highlight recent advances in geochemistry as informed by copper and other metal isotope systems as they are applied to various geological and environmental settings. Our vision for this Special Issue is not defined by a specific environment or geological time period, but is united by the measurement of copper or other metal isotope systems. We welcome original studies that highlight the value metal isotope systems provide in furthering our understand of natural processes, new approaches in metal isotope geochemistry (including novel analytical methods), high-resolution analysis (with an emphasis on in-situ laser ablation analysis), and experimental studies. 

Dr. Dan Asael
Dr. Leslie Robbins
Guest Editors

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Keywords

  • metal isotopes
  • isotope geochemistry
  • laser ablation

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Published Papers (7 papers)

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Research

30 pages, 3693 KiB  
Article
Iron Isotope Compositions of Coexisting Sulfide and Silicate Minerals in Sudbury-Type Ores from the Jinchuan Ni-Cu Sulfide Deposit: A Perspective on Possible Core-Mantle Iron Isotope Fractionation
by Peiyao Wang, Yaoling Niu, Pu Sun, Xiaohong Wang, Pengyuan Guo, Hongmei Gong, Meng Duan, Fangyu Shen, Yining Shi, Song Xue, Yanhong Chen and Li Shan
Minerals 2021, 11(5), 464; https://doi.org/10.3390/min11050464 - 28 Apr 2021
Cited by 11 | Viewed by 3274
Abstract
Many studies have shown that the average iron (Fe) isotope compositions of mantle-derived rocks, mantle peridotite and model mantle are close to those of chondrites. Therefore, it is considered that chondrite values represent the bulk Earth Fe isotope composition. However, this is a [...] Read more.
Many studies have shown that the average iron (Fe) isotope compositions of mantle-derived rocks, mantle peridotite and model mantle are close to those of chondrites. Therefore, it is considered that chondrite values represent the bulk Earth Fe isotope composition. However, this is a brave assumption because nearly 90% of Fe of the Earth is in the core, where its Fe isotope composition is unknown, but it is required to construct bulk Earth Fe isotope composition. We approach the problem by assuming that the Earth’s core separation can be approximated in terms of the Sudbury-type Ni-Cu sulfide mineralization, where sulfide-saturated mafic magmas segregate into immiscible sulfide liquid and silicate liquid. Their density/buoyancy controlled stratification and solidification produced net-textured ores above massive ores and below disseminated ores. The coexisting sulfide minerals (pyrrhotite (Po) > pentlandite (Pn) > chalcopyrite (Cp)) and silicate minerals (olivine (Ol) > orthopyroxene (Opx) > clinopyroxene (Cpx)) are expected to hold messages on Fe isotope fractionation between the two liquids before their solidification. We studied the net-textured ores of the Sudbury-type Jinchuan Ni-Cu sulfide deposit. The sulfide minerals show varying δ56Fe values (−1.37–−0.74‰ (Po) < 0.09–0.56‰ (Cp) < 0.53–1.05‰ (Pn)), but silicate minerals (Ol, Opx, and Cpx) have δ56Fe values close to chondrites (δ56Fe = −0.01 ± 0.01‰). The heavy δ56Fe value (0.52–0.60‰) of serpentines may reflect Fe isotopes exchange with the coexisting pyrrhotite with light δ56Fe. We obtained an equilibrium fractionation factor of Δ56Fesilicate-sulfide ≈ 0.51‰ between reconstructed silicate liquid (δ56Fe ≈ 0.21‰) and sulfide liquid (δ56Fe ≈ −0.30‰), or Δ56Fesilicate-sulfide ≈ 0.36‰ between the weighted mean bulk-silicate minerals (δ56Fe[0.70ol,0.25opx,0.05cpx] = 0.06‰) with weighted mean bulk-sulfide minerals (δ56Fe ≈ −0.30‰). Our study indicates that significant Fe isotope fractionation does take place between silicate and sulfide liquids during the Sudbury-type sulfide mineralization. We hypothesize that significant iron isotope fractionation must have taken place during core–mantle segregation, and the bulk Earth may have lighter Fe isotope composition than chondrites although Fe isotope analysis on experimental sulfide-silicate liquids produced under the varying mantle depth conditions is needed to test our results. We advocate the importance of further research on the subject. Given the close Fe-Ni association in the magmatic mineralization and the majority of the Earth’s Ni is also in the core, we infer that Ni isotope fractionation must also have taken place during the core separation that needs attention. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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18 pages, 3529 KiB  
Article
Iron Isotope Fractionation during Skarn Cu-Fe Mineralization
by Song Xue, Yaoling Niu, Yanhong Chen, Yining Shi, Boyang Xia, Peiyao Wang, Hongmei Gong, Xiaohong Wang and Meng Duan
Minerals 2021, 11(5), 444; https://doi.org/10.3390/min11050444 - 22 Apr 2021
Cited by 8 | Viewed by 3439
Abstract
Fe isotopes have been applied to the petrogenesis of ore deposits. However, the behavior of iron isotopes in the mineralization of porphyry-skarn deposits is still poorly understood. In this study, we report the Fe isotopes of ore mineral separations (magnetite, pyrite, chalcopyrite and [...] Read more.
Fe isotopes have been applied to the petrogenesis of ore deposits. However, the behavior of iron isotopes in the mineralization of porphyry-skarn deposits is still poorly understood. In this study, we report the Fe isotopes of ore mineral separations (magnetite, pyrite, chalcopyrite and pyrrhotite) from two different skarn deposits, i.e., the Tonglvshan Cu-Fe skarn deposit developed in an oxidized hydrothermal system and the Anqing Cu skarn deposit developed in a reduced hydrothermal system. In both deposits, the Fe isotopes of calculated equilibrium fluids are lighter than those of the intrusions responsible for the skarn and porphyry mineralization, corroborating the “light-Fe fluid” hypothesis. Interestingly, chalcopyrite in the oxidized-Tonglvshan skarn deposit has lighter Fe than chalcopyrite in the reduced-Anqing skarn deposit, which is best understood as the result of the prior precipitation of magnetite (heavy Fe) from the ore fluid in the oxidized-Tonglvshan systems and the prior precipitation of pyrrhotite (light Fe) from the ore fluid in the reduced-Anqing system. The δ56Fe for pyrite shows an inverse correlation with δ56Fe of magnetite in the Tonglvshan. In both deposits, the Fe isotope fractionation between chalcopyrite and pyrite is offset from the equilibrium line at 350 °C and lies between the FeS-chalcopyrite equilibrium line and pyrite-chalcopyrite equilibrium line at 350 °C. These observations are consistent with the FeS pathway towards pyrite formation. That is, Fe isotopes fractionation during pyrite formation depends on a path from the initial FeS-fluid equilibrium towards the pyrite-fluid equilibrium due to the increasing extent of Fe isotopic exchange with fluids. This finding, together with the data from other deposits, allows us to propose that the pathway effect of pyrite formation in the Porphyry-skarn deposit mineralization is the dominant mechanism that controls Fe isotope characteristics. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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25 pages, 3189 KiB  
Article
Iron Isotopes Reveal a Benthic Iron Shuttle in the Palaeoproterozoic Zaonega Formation: Basinal Restriction, Euxinia, and the Effect on Global Palaeoredox Proxies
by Kaarel Mänd, Stefan V. Lalonde, Kärt Paiste, Marie Thoby, Kaarel Lumiste, Leslie J. Robbins, Timmu Kreitsmann, Alexander E. Romashkin, Kalle Kirsimäe, Aivo Lepland and Kurt O. Konhauser
Minerals 2021, 11(4), 368; https://doi.org/10.3390/min11040368 - 31 Mar 2021
Cited by 6 | Viewed by 4107
Abstract
The Zaonega Formation in northwest Russia (~2.0 billion years old) is amongst the most complete successions that record the middle of the Palaeoproterozoic era. As such, geochemical data from the formation have played a central role in framing the debate over redox dynamics [...] Read more.
The Zaonega Formation in northwest Russia (~2.0 billion years old) is amongst the most complete successions that record the middle of the Palaeoproterozoic era. As such, geochemical data from the formation have played a central role in framing the debate over redox dynamics in the aftermath of the Great Oxidation Event (GOE). However, uncertainty over local redox conditions and the degree of hydrographic restriction in the formation has led to contradictory interpretations regarding global oxygen (O2) fugacity. Here, we provide new iron (Fe) isotope data together with major and trace element concentrations to constrain the local physiochemical conditions. The Zaonega Formation sediments show authigenic Fe accumulation (Fe/Al ≫ 1 wt.%/wt.%) and δ56Fe ranging from −0.58‰ to +0.60‰. Many of the data fall on a negative Fe/Al versus δ56Fe trend, diagnostic of a benthic Fe shuttle, which implies that Zaonega Formation rocks formed in a redox-stratified and semi-restricted basin. However, basin restriction did not coincide with diminished trace metal enrichment, likely due to episodes of deep-water exchange with metal-rich oxygenated seawater, as evidenced by simultaneous authigenic Fe(III) precipitation. If so, the Onega Basin maintained a connection that allowed its sediments to record signals of global ocean chemistry despite significant basinal effects. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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20 pages, 46214 KiB  
Article
Iron and Carbon Isotope Constraints on the Formation Pathway of Iron-Rich Carbonates within the Dagushan Iron Formation, North China Craton
by Xiaoxue Tong, Kaarel Mänd, Yuhao Li, Lianchang Zhang, Zidong Peng, Qiang Wu, Pengbo Li, Mingguo Zhai, Leslie J. Robbins, Changle Wang and Kurt O. Konhauser
Minerals 2021, 11(1), 94; https://doi.org/10.3390/min11010094 - 19 Jan 2021
Cited by 8 | Viewed by 4720
Abstract
Banded iron formations (BIFs) are enigmatic chemical sedimentary rocks that chronicle the geochemical and microbial cycling of iron and carbon in the Precambrian. However, the formation pathways of Fe carbonate, namely siderite, remain disputed. Here, we provide photomicrographs, Fe, C and O isotope [...] Read more.
Banded iron formations (BIFs) are enigmatic chemical sedimentary rocks that chronicle the geochemical and microbial cycling of iron and carbon in the Precambrian. However, the formation pathways of Fe carbonate, namely siderite, remain disputed. Here, we provide photomicrographs, Fe, C and O isotope of siderite, and organic C isotope of the whole rock from the ~2.52 Ga Dagushan BIF in the Anshan area, China, to discuss the origin of siderite. There are small magnetite grains that occur as inclusions within siderite, suggesting a diagenetic origin of the siderite. Moreover, the siderites have a wide range of iron isotope compositions (δ56FeSd) from −0.180‰ to +0.463‰, and a relatively negative C isotope composition (δ13CSd = −6.20‰ to −1.57‰). These results are compatible with the reduction of an Fe(III)-oxyhydroxide precursor to dissolved Fe(II) through microbial dissimilatory iron reduction (DIR) during early diagenesis. Partial reduction of the precursor and possible mixing with seawater Fe(II) could explain the presence of siderite with negative δ56Fe, while sustained reaction of residual Fe(III)-oxyhydroxide could have produced siderite with positive δ56Fe values. Bicarbonate derived from both DIR and seawater may have provided a C source for siderite formation. Our results suggest that microbial respiration played an important role in the formation of siderite in the late Archean Dagushan BIF. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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20 pages, 1679 KiB  
Article
Molybdenum Isotope Constraints on the Origin of Vanadium Hyper-Enrichments in Ediacaran–Phanerozoic Marine Mudrocks
by Alexandra Kunert, Johnathan Clarke and Brian Kendall
Minerals 2020, 10(12), 1075; https://doi.org/10.3390/min10121075 - 30 Nov 2020
Cited by 15 | Viewed by 3414
Abstract
Vanadium is an important redox-sensitive trace metal for paleoenvironmental reconstructions. Modern organic-rich sediments persistently contain sediment V enrichments <500 μg/g, but many ancient marine organic-rich mudrocks record enrichments >500 μg/g. Previous studies propose that ancient V enrichments of these magnitudes (“V hyper-enrichments”) were [...] Read more.
Vanadium is an important redox-sensitive trace metal for paleoenvironmental reconstructions. Modern organic-rich sediments persistently contain sediment V enrichments <500 μg/g, but many ancient marine organic-rich mudrocks record enrichments >500 μg/g. Previous studies propose that ancient V enrichments of these magnitudes (“V hyper-enrichments”) were deposited from hyper-sulfidic bottom-waters with higher H2S levels (≥10 mM) than observed in modern euxinic basins. To test the importance of hyper-sulfidic conditions for generating V hyper-enrichments, we compare V concentrations with Mo isotope (δ98Mo) compositions from mudrock samples ranging in age from Ediacaran to Pleistocene. In the modern ocean, sediments deposited from strongly euxinic bottom waters ([H2S]aq > 11 μM) closely record global seawater δ98Mo because conversion of molybdate to tri- and tetra-thiomolybdate is quantitative. By contrast, large Mo isotope fractionations occur during Mo adsorption to Fe-Mn particulates or because of incomplete formation of the most sulfidic thiomolybdates in weakly euxinic settings ([H2S]aq < 11 μM), which both favor removal of lighter-mass Mo isotopes to sediments. We find multiple examples when mudrocks with V hyper-enrichments are associated with a wide range of δ98Mo for a single time interval, including values at or below oceanic input δ98Mo (0.3–0.7‰). This observation suggests significant isotopic offset from reasonable seawater values (typically ≥1.0‰). Thus, we conclude that hyper-sulfidic conditions were not responsible for many V hyper-enrichments in Ediacaran–Phanerozoic mudrocks. Instead, sediment V hyper-enrichments can be explained by high Fe-Mn particulate fluxes to weakly euxinic sediments or by moderately restricted euxinic settings with strongly euxinic ([H2S]aq > 11 μM but not necessarily > 10 mM) or weakly euxinic (with slow clastic sedimentation rates and high organic carbon fluxes) bottom waters where vigorous water exchange provides a continuous V supply from the open ocean. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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17 pages, 3282 KiB  
Article
Iron Isotopes Constrain the Metal Sources of Skarn Deposits: A Case Study from the Han-Xing Fe Deposit, China
by Bin Zhu, Hongfu Zhang, M. Santosh, Benxun Su, Pengfei Zhang, Chunming Han and Yongsheng He
Minerals 2020, 10(11), 951; https://doi.org/10.3390/min10110951 - 26 Oct 2020
Cited by 5 | Viewed by 2968
Abstract
Magmatic fluids and leaching of rocks are regarded as the two sources of magmatic hydrothermal deposits, but their relative contributions to the metals in the deposits are still unclear. In this study, we combine major elements and Fe isotopes in two sets of [...] Read more.
Magmatic fluids and leaching of rocks are regarded as the two sources of magmatic hydrothermal deposits, but their relative contributions to the metals in the deposits are still unclear. In this study, we combine major elements and Fe isotopes in two sets of rocks from the Han-Xing iron skarn deposit in China to constrain the iron sources. The positive correlation between the δ56Fe and ∑Fe2O3/TiO2 of altered diorites (∑Fe2O3 refers to the total iron) demonstrates that heavy Fe isotopes are preferentially leached from diorites during hydrothermal alteration. However, except for the pyrite, all the rocks and minerals formed in the skarn deposit are enriched in the light Fe isotope relative to the fresh/less altered diorites. Therefore, besides the leaching of rocks, the Fe isotopically light magmatic fluid also provides a large quantity of iron for this deposit. Based on the mass balance calculation, we conclude that iron from magmatic fluid is almost 2.6 times as large as that from the leaching of rocks. This is the first study to estimate the relative proportions of iron sources for Fe deposits by using Fe isotopes. Here, we propose that the high δ56Fe of magmatic intrusions combining the positive correlation between their ∑Fe2O3/TiO2 and δ56Fe could be taken as a fingerprint of exsolution or interaction with magmatic fluids, which contributes to the exploration of magmatic hydrothermal ore deposits. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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24 pages, 3341 KiB  
Article
Chromium Isotope Systematics in Modern and Ancient Microbialites
by Sylvie Bruggmann, Alexandra S. Rodler, Robert M. Klaebe, Steven Goderis and Robert Frei
Minerals 2020, 10(10), 928; https://doi.org/10.3390/min10100928 - 20 Oct 2020
Cited by 7 | Viewed by 3543
Abstract
Changes in stable chromium isotopes (denoted as δ53Cr) in ancient carbonate sediments are increasingly used to reconstruct the oxygenation history in Earth’s atmosphere and oceans through time. As a significant proportion of marine carbonate older than the Cambrian is microbially-mediated, the [...] Read more.
Changes in stable chromium isotopes (denoted as δ53Cr) in ancient carbonate sediments are increasingly used to reconstruct the oxygenation history in Earth’s atmosphere and oceans through time. As a significant proportion of marine carbonate older than the Cambrian is microbially-mediated, the utility of δ53Cr values in ancient carbonates hinges on whether these sediments accurately capture the isotope composition of their environment. We report Cr concentrations (Cr) and δ53Cr values of modern marginal marine and non-marine microbial carbonates. These data are supported by stable C and O isotope compositions, as well as rare earth elements and yttrium (REY) concentrations. In addition, we present data on ancient analogs from Precambrian strata. Microbial carbonates from Marion Lake (Australia, δ53Cr ≈ 0.99‰) and Mono Lake (USA, ≈0.78‰) display significantly higher δ53Cr values compared with ancient microbialites from the Andrée Land Group in Greenland (720 Ma, ≈0.36‰) and the Bitter Springs Formation in Australia (800 Ma, ≈−0.12‰). The δ53Cr values are homogenous within microbialite specimens and within individual study sites. This indicates that biological parameters, such as vital effects, causing highly variable δ53Cr values in skeletal carbonates, do not induce variability in δ53Cr values in microbialites. Together with stable C and O isotope compositions and REY patterns, δ53Cr values in microbialites seem to be driven by environmental parameters such as background lithology and salinity. In support, our Cr and δ53Cr results of ancient microbial carbonates agree well with data of abiotically precipitated carbonates of the Proterozoic. If detrital contamination is carefully assessed, microbialites have the potential to record the δ53Cr values of the waters from which they precipitated. However, it remains unclear if these δ53Cr values record (paleo-) redox conditions or rather result from other physico-chemical parameters. Full article
(This article belongs to the Special Issue Copper and Other Metallic Isotope Systems)
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