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Article

Coupled Eu Anomalies and Fe Isotopes Reveal a Hydrothermal Iron Source for Superior-Type Iron Formations: A Case Study from the Wilgena Hill Iron Formation, South Australia

by
Shuo Chen
1,2,
Jian Sun
2,*,
Xiangkun Zhu
2 and
Yuelong Chen
1
1
School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China
2
MNR Key Laboratory of Isotope Geology, State Key Laboratory of Deep Earth and Mineral Exploration, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China
*
Author to whom correspondence should be addressed.
Minerals 2025, 15(8), 824; https://doi.org/10.3390/min15080824 (registering DOI)
Submission received: 30 April 2025 / Revised: 20 July 2025 / Accepted: 29 July 2025 / Published: 2 August 2025
(This article belongs to the Special Issue Geochemical, Isotopic, and Biotic Records of Banded Iron Formations)
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Abstract

Superior-type iron formations (IFs) represent a globally significant source of iron ore; yet, their origin remains a subject of ongoing debate. Early models proposed a continental weathering source for the iron, whereas later interpretations—mainly supported by positive europium (Eu) anomalies—favored a hydrothermal source. However, the hydrothermal model largely relies on REE systematics, and whether iron and REEs in Superior-type IFs share the same source remains uncertain. As iron isotopes directly trace the sources and fractionation history of iron, a spatial co-variation between Fe isotopes and Eu anomalies would shed new light on the iron source issue of IFs. In this study, we present new Fe isotope and REE data from the drill core WILDD004 at Wilgena Hill and integrate them with reported data for two additional drill cores: HKDD4 (Hawks Nest) and GWDD1 (Giffen Well). All three cores are stratigraphically equivalent to the Wilgena Hill Jaspilite Formation but span a lateral distance of ~100 km across the Gawler Craton, South Australia. While the Hawks Nest and Giffen Well samples exhibit both positive Eu anomalies and elevated δ56Fe values, the Wilgena Hill samples show positive yet smaller Eu/Eu* (1.17–2.41) and negative δ56Fe values (−0.60‰ to −1.63‰). The consistent presence of Eu anomalies and the systematic spatial correlation between δ56Fe and Eu/Eu* across all three locations provide direct, Fe-based geochemical evidence for a hydrothermal source of iron in this Superior-type IF.

1. Introduction

Iron formations (IFs) are marine chemical sedimentary rocks characterized by high iron (15–40 wt% Fe) and silica (40–60 wt% SiO2) content, predominantly deposited during the Precambrian [1]. They are broadly classified into Algoma type and Superior type based on their depositional environments [2]. It is now widely recognized that Algoma-type IFs formed near active volcanic arcs, with iron supplied by high-temperature hydrothermal fluids associated with seafloor spreading or volcanic activity [3,4,5,6].
In contrast, the iron source for Superior-type IFs remains controversial. Early models proposed that iron was mobilized from continental sources via chemical weathering under an anoxic atmosphere [1,7]. This hypothesis is supported by certain neodymium isotopic signatures suggesting continental inputs [8,9,10]. However, it has since been argued that continental weathering alone cannot account for the massive iron fluxes recorded in large IF basins, such as the Hamersley, leading to the proposal that hydrothermal fluids—similar to those observed in modern mid-ocean ridges—provided the necessary iron. Supporting this interpretation are widespread positive Eu anomalies in many Superior-type IFs. High-temperature hydrothermal fluids typically show Eu enrichment relative to other rare earth elements (REEs) due to reduction of Eu3+ at temperatures of >250 °C [11,12,13]. Consequently, these anomalies are widely regarded as geochemical tracers of hydrothermal iron sources [5,14,15,16].
Despite the growing consensus around a hydrothermal contribution for the iron source of IFs, most of this understanding is inferred from REE patterns. Whether iron and REEs in Superior-type IFs were derived from the same hydrothermal source remains unresolved. In this regard, iron isotopes provide a more direct geochemical tracer. Hydrothermal Fe2+ typically exhibits δ56Fe values near −0.5‰; partial oxidation of Fe(II) enriches heavy δ56Fe values in Fe(III) precipitates, with equilibrium Fe isotope fractionation between Fe(III) precipitates and Fe(II) fluids up to 3‰ in δ56Fe values [17]. This fractionation during Fe(III) precipitation can be modeled by a Rayleigh fractionation model. Assuming relatively constant δ56Fe values in hydrothermal fluids, the isotopic composition of Fe oxides is controlled by the degree of Fe precipitation, which depends on the redox state of the surrounding water and the extent of Fe(II) transport in the fluids. Near hydrothermal sources, Fe oxides precipitate with heavier δ56Fe values, leaving residual fluids isotopically lighter. Distal IFs consequently inherit lighter δ56Fe signatures during precipitation. Concurrently, seawater dilution weakens Eu anomalies during fluid transport. Thus, a positive spatial correlation between δ56Fe and Eu anomalies across a basin indicates derivation from a common hydrothermal source.
Here, we investigated the Wilgena Hill IF in the Gawler Craton of South Australia, a well-preserved Superior-type IF. We present new Fe isotope and REE data from the WILDD004 drill core at Wilgena Hill and integrate these with existing data from two additional cores (HKDD4 at Hawks Nest and GWDD1 at Giffen Well), all part of the stratigraphically equivalent Wilgena Hill Jaspilite Formation. These three locations span ~100 km across the craton, allowing us to assess spatial variations in Fe and REE geochemistry. Our results reveal a systematic spatial correlation between δ56Fe and Eu/Eu* values, providing direct geochemical evidence that supports a hydrothermal source for the iron in this Superior-type IF.

2. Geological Background

The Precambrian strata of Australia are predominantly distributed across three major cratons: the North Australian Craton, the South Australian Craton and the West Australian Craton [18,19]. This study focuses on the Gawler Craton, which is located in the western part of the South Australian Craton. The Gawler Craton is primarily composed of Mesoarchean to Mesoproterozoic rocks, with its internal crustal architecture characterized by a semi-arcuate-shaped Archean nucleus surrounded by Paleo- and Mesoproterozoic successions (Figure 1A).
The IF investigated in this study is situated within the central Gawler Craton (Figure 1B), hosted in the Wilgena Hill Jaspilite Formation—the oldest recognized geological unit in the region. Despite its significance, precise geochronological constraints on the IF’s age remain limited. Deposition is broadly bracketed between ~2440 Ma, corresponding to the age of the underlying Mulgathing Complex, and 1715 ± 9 Ma, the age of minor rhyolite and pebbly conglomerate within the overlying Labyrinth Formation [22]. The Labyrinth Formation unconformably overlies the thick-bedded quartzites of the Eba Formation [23], with basal conglomerates containing clasts derived from the Wilgena Hill Jaspilite Formation. The youngest metasedimentary unit, the Tarcoola Formation, comprises conglomerate, quartzite and shale intercalated with 1656 ± 7 Ma dacitic-to-andesitic water-lain tuffs [24] (Figure 2A).
IFs hosted within the Wilgena Hill Jaspilite Formation extend discontinuously over ~150 km, forming strike ridges from the Hawks Nest district in the north through Griffen Well to the Coolybring, Wilgena Hill and Hicks Hill prospects in the south (Figure 1B). This deposit is estimated to contain potential reserves of approximately 581.5 million tonnes [27]. Documented occurrences include the Hawks Nest, Griffen Well and Wilgena Hill prospects, with this study focusing on drill cores WILDD004 (Wilgena Hill) and prior studies focusing on drill cores HKDD4 (Hawks Nest) and GWDD1 (Griffen Well) [28]. The Wilgena Hill IF is entirely hosted by sedimentary rocks. Conglomerates overlie the IF in GWDD1 and HKDD4 (Figure 2C,D), whereas siltstone caps the IF in WILDD004 (Figure 2B). Volcanic rocks are rarely present throughout the stratigraphic sequence, supporting the classification of the Wilgena Hill IF as a Superior-type IF [21,29].

3. Petrography

The IF samples in the study area are extremely fine-grained (0.01–0.1 mm) and consist of microbands (0.1–1.0 mm thick) of dark gray to black iron oxide (predominantly hematite) interlayered with similarly thin laminae of red chert or jasper (Figure 3B). These laminae occur as discrete microbands or aggregate into iron-rich or chert-dominated mesobands, which range from 1 to 5 cm in thickness (Figure 3B). The mineral assemblage is dominated by hematite, quartz and jasper (Figure 3C,D). Stratigraphically overlying the BIF are black and gray siltstones (Figure 3A).

4. Methods

4.1. Sample Collection and Preparation

We measured the major element, trace element and Fe isotope compositions of 9 samples from the drill core WILDD004 (30°38′39″ S, 133°36′21″ E) through the Wilgena Hill IF (provided by the Geological Survey of South Australia), including 8 iron formation samples and 1 shale sample. In addition to WIL4-1 and WIL4-5, all other samples were analyzed separately according to the red (jasper) and black (ironstone) bands. Care was taken to exclude veins and highly weathered material to ensure that only the primary unaltered sediments were included in the analyses. Samples were finely ground to ~200 mesh using an agate mortar.

4.2. Major and Trace Element Analyses

Whole-rock major and trace element analyses of bulk samples were undertaken by ALS Chemex Inc. (Guangzhou, China), using the M61-MS81 and ME-XRF26s method. For major element analysis, powdered samples were mixed with Lithium Borate Flux (1:1 Li2B4O7–LiBO2) and melted in an auto fluxer at 1100 °C; once the melts had cooled, their compositions were determined by X-ray fluorescence analysis. The detection limit for major elements was approximately 0.01 wt%. Accuracy was monitored relative to reference material SARM-5 (South African Bureau of Standards, Pretoria, South Africa), with relative errors and deviations below 5%.
For trace elements analysis, a small amount of powdered sample was melted at temperatures exceeding 1025 °C using a mixed flux (Li2B4O7–LiBO2, guaranteed reagent GR). Subsequently, the fused bead was dissolved in a mixture of HNO3, HF and HCl, and the final solution was diluted with 2% HNO3 to a fixed volume appropriate for analysis using ICP-MS. Certified standards OREAS 120 (OREAS, Baywater North, Australia) and OREAS-45e (OREAS, Baywater North, Australia) were used as references during the analyses. The relative error and deviation were less than 10%.

4.3. Iron Isotope Analyses

Dissolution and separation of Fe were performed in the Laboratory of Isotope Geology, Chinese Academy of Geological Sciences. Approximately 20 mg–50 mg of each powdered sample was weighed into a Teflon beaker and fully digested at 120 °C for 48 h in a solution of 1 mL concentrated HNO3 and 3 mL concentrated HF. After complete dissolution, the sample solution was treated with concentrated HCl to convert the cations to a chloride form. The sample solution was loaded onto the resin bed in 6N HCl (mixed with 0.001% H2O2) in order to remove ions other than Fe and Zn. Following this, 2N HCl (mixed with 0.001% H2O2) was used to strip Fe.
Fe isotope ratios were determined on a Nu plasma high-resolution (HR) multicollector (MC)-ICP-MS in middle-resolution mode using the standard-sample bracketing (SSB) approach [30].
The Fe isotope values in this study are reported as per mil (‰) relative to the standard IRMM-014 [31], as follows:
δ56FeIRMM-014(‰) = [(56Fe/54Fe) sample/(56Fe/54Fe) IRMM-014-1] ×103
δ57FeIRMM-014(‰) = [(57Fe/54Fe) sample/(57Fe/54Fe) IRMM-014-1] ×103
The long-term external reproducibility for δ56Fe was better than 0.08‰ at two standard deviations [30]. The δ56Fe values of international basaltic standard reference materials were determined to be 0.07 ± 0.05‰ (reference material BCR-2; 2SD, n = 4) and 0.12 ± 0.04‰ (reference material GSR-3; 2SD, n = 3), consistent with the results of Craddock and Dauphas [32].

5. Results

5.1. Major Element Compositions

The major element compositions of the Wilgena Hill IF samples from the drill core WILDD004 are shown in Table 1. The IF samples are mainly composed of iron (ironstone: 71.82–82.83 wt% Fe2O3; jasper: 19.46–24.99 wt% Fe2O3) and silica (ironstone: 17.98–31.45 wt% SiO2; jasper: 73.50–79.34 wt% SiO2). Samples exhibit low aluminum contents; Al2O3 is lower than 1 wt% in both the ironstone and the jasper samples.

5.2. Trace Element Compositions

Trace element compositions are presented in Table 1. The REE compositions of the Wilgena Hill IF were normalized to post-Archean Australian shale [33], and the following equations were used to quantify the Eu anomalies: Eu/Eu* = EuPAAS/(0.67 SmPAAS + 0.33 GdPAAS). The samples of the Wilgena Hill IF had positive Eu anomalies (ironstone: 1.17–2.41 Eu/Eu*; jasper: 1.39–2.35 Eu/Eu*) (Figure 4A). In the WILDD004 drill hole, Eu anomalies generally decrease from the base to the top of the sequence (Figure 5A)—a trend that is also observed in the GWDD1 drill hole (Figure 5B).

5.3. Fe Isotope Compositions

The Fe isotopic compositions of the Wilgena Hill IF from the drill core WILDD004 are shown in Table 2, which show very low δ56Fe values. The δ56Fe values of the ironstone samples range from −0.60‰ to −1.42‰, with a mean of −0.92‰. The δ56Fe values of the jasper samples range from −0.73‰ to −1.63‰, with a mean of −1.12‰. In the WILDD004 and GWDD1 section, the δ56Fe values tend to decrease, while Eu anomalies tend to increase downward (Figure 5).

6. Discussion

6.1. Iron Source of the Wilgena Hill Iron Formation

The source of iron in Superior-type IFs has been debated for decades. While Algoma-type IFs are widely recognized as hydrothermal in origin, models for Superior-type IFs have ranged from enhanced continental weathering under anoxic atmospheric conditions [1,7] to upwelling of hydrothermally enriched deep waters [34], or more recently, localized hydrothermal input [16]. The Wilgena Hill IF exhibits several geochemical characteristics consistent with a hydrothermal source.
One of the most compelling indicators is the consistently positive Eu anomalies observed in samples from all three drill cores, including WILDD004, GWDD1 and HKDD4 (Figure 4A–C). Positive Eu anomalies are widely interpreted as fingerprints of high-temperature hydrothermal fluids, as Eu2+ is preferentially mobilized under reducing conditions [14]. Furthermore, the low Al2O3 contents (<1 wt%) in the Wilgena Hill IF further support a negligible contribution from terrigenous clastic input, reducing the likelihood of significant continental Fe sources.
Hydrothermally sourced iron in IFs can derive from either localized hydrothermal vents or seawater upwelling. The pronounced Eu anomalies observed in the Wilgena Hill IFs, particularly in the HKDD4 drill core (Eu/Eu* > 3.0; Figure 5C), align with values characteristic of Algoma-type IFs (Figure 6). This suggests that iron in the Wilgena Hill IFs originated from localized hydrothermal fluids. This interpretation aligns with studies from other Superior-type IFs, such as those in the Animikie Basin in the Lake Superior region and the Jingtieshan IF in the North Qilian Orogenic Belt, where positive Eu anomalies reflect proximal hydrothermal iron sources rather than seawater upwelling [16,35].

6.2. Coupled δ56Fe–Eu/Eu* and Hydrothermal Transport

Beyond rare earth element systematics, our data provide direct Fe-based evidence for a hydrothermal origin. The spatial variation in Fe isotopic composition (δ56Fe) across the three drill cores reveals a clear trend: samples from HKDD4 in the north show the heaviest Fe isotopic signatures (mean δ56Fe = +0.85‰) (Figure 5C); samples from GWDD1 in the middle show intermediate values (mean δ56Fe = −0.15‰) (Figure 5B); and samples from WILDD004 in the south record the lightest Fe isotopes (mean δ56Fe = −0.92‰) (Figure 5A). Importantly, these shifts in Fe isotopes correspond closely with changes in Eu anomalies across the same transect (Figure 6). The data show a Pearson correlation coefficient of 0.464, with a p-value of 0.0075. This indicates a moderate positive linear correlation between Eu/Eu* and δ56Fe, which is statistically significant (p < 0.01).
We interpret this spatial pattern as the result of Fe isotope fractionation during hydrothermal transport and partial oxidation. Near the vent site (HKDD4), pronounced significant Eu anomalies, rapid oxidation and precipitation of Fe3+ phases sequester heavier Fe isotopes into sediments, leaving lighter Fe2+ in the residual fluid. As hydrothermal fluids are transported away from the source, dilution of hydrothermal fluids by seawater during hydrothermal transport leads to decreases in Eu anomalies, while continued oxidation and progressive Fe loss lead to lighter δ56Fe values being recorded further downflow (GWDD1 and WILDD004). The co-variation in δ56Fe and Eu/Eu* thus reflects both the changing distance from the hydrothermal source and the extent of Fe precipitation during transport (Figure 7).
It is acknowledged that although the overall spatial trend between δ56Fe and Eu/Eu* reveals a first-order control by hydrothermal fluid proximity, local deviations from this trend are present within individual drill cores. For an individual drill hole, δ56Fe and Eu/Eu* are positively corelated for HKDD4 but negatively corelated for WILDD004 (Figure 6). These irregularities likely result from second-order processes, such as fluctuating redox conditions. Assuming that the hydrothermal source remains unchanged, δ56Fe variability within individual drill cores is primarily controlled by the redox conditions. In the HKDD4 drill hole, located proximal to the hydrothermal vent, redox fluctuations are largely modulated by variations in hydrothermal fluid flux due to a higher hydrothermal/seawater mixing ratio. Enhanced hydrothermal activity increases Eu/Eu* values and delivers more reducing fluids, creating anoxic conditions where limited Fe2+ oxidation yields heavier δ56Fe signatures. Conversely, diminished hydrothermal activity produces more oxic conditions, promoting greater Fe2+ precipitation and lighter δ56Fe values. This dynamic results in a positive correlation between δ56Fe and Eu/Eu* in HKDD4. In contrast, distal drill holes (GWDD1 and WILDD004) experience reduced hydrothermal input, making δ56Fe variability more strongly influenced by seawater redox changes alone, which weakens the δ56Fe–Eu/Eu* correlation. The negative relationship observed in WILDD004 remains challenging to interpret. Notably, the jasper and ironstone samples from WIL4-16 and WIL4-22 exhibit anomalously light δ56Fe values (−1.93‰ to −2.36‰). Excluding these outliers eliminates the apparent trend between Eu/Eu* and δ56Fe.
This mechanism is consistent with Fe isotope fractionation models previously proposed for IFs [38] but has rarely been demonstrated at spatial scales of >50 km using coordinated REE and Fe isotope datasets. Our results represent a rare, direct geochemical validation of hydrothermal Fe sourcing in a Superior-type IF.

6.3. Implications for Genetic Models of Superior-Type IFs

Our findings have significant implications for the interpretation of Superior-type IF genesis. While previous models have inferred hydrothermal input from REE patterns or modern analogs, this study provides Fe-based isotopic evidence that complements and strengthens the hydrothermal hypothesis.
The consistent Eu anomalies, combined with the spatial correlation between Eu/Eu* and δ56Fe, indicate that both Fe and REEs in the Wilgena Hill IF were derived from a shared hydrothermal source. This coupling provides strong evidence that iron and REEs were introduced into the basin through the same hydrothermal processes.
Furthermore, the Wilgena Hill case supports the growing recognition that localized hydrothermal venting, rather than deep-ocean upwelling, may have played a dominant role in supplying Fe to some Superior-type IFs [16]. These findings suggest that Superior-type IFs may not be as distinct from Algoma-type IFs in their Fe sourcing as previously thought but rather differ primarily in basinal setting and spatial transport dynamics.

7. Conclusions

This study presents a coupled iron isotope and rare earth element (REE) investigation of the Wilgena Hill Iron Formation, a representative Superior-type IF located in the Gawler Craton, South Australia. By integrating new Fe isotope and Eu anomaly data from three spatially distributed drill cores—HKDD4 (Hawks Nest), GWDD1 (Giffen Well) and WILDD004 (Wilgena Hill)—we evaluate the source of iron in this large-scale Precambrian chemical sediment. Our results reveal the following key findings:
(1)
All three drill cores exhibit positive Eu anomalies, indicative of hydrothermal contributions across the basin.
(2)
A clear spatial co-variation exists between δ56Fe and Eu/Eu*. This provides direct geochemical evidence that both iron and REEs were sourced from the same hydrothermal fluids and fractionated during lateral transport and oxidation in the basin.
These results confirm that hydrothermal venting was the primary source of iron in this Superior-type IF, providing the first Fe-based isotopic validation for a long-standing hypothesis largely inferred from REE systematics. Moreover, the spatial resolution of our dataset (~100 km) demonstrates that Fe isotopes and Eu anomalies can act as coupled tracers of hydrothermal input and depositional gradients in ancient sedimentary systems.
Our findings have broader implications for the study of Precambrian IFs, suggesting that localized hydrothermal systems may have played a more significant role in the genesis of Superior-type IFs than previously recognized and that their distinction from Algoma-type IFs may be less genetic and more environmental. Future studies combining Fe, Nd and REE proxies across multiple basins are essential to further unravel the global patterns of Fe sourcing and redox conditions during the Precambrian.

Author Contributions

Conceptualization, S.C., J.S. and X.Z.; Investigation, S.C. and J.S.; Writing—original draft, S.C.; Writing—review & editing, S.C., J.S. and X.Z.; Supervision, J.S., X.Z. and Y.C.; Funding acquisition, X.Z. All authors have read and agreed to the published version of the manuscript.

Funding

This work was financially supported by the National Natural Science Foundation of China (Grant No. U2244210) and the National Key R&D Program of China (2019YFA0708404).

Data Availability Statement

Data are contained within the article.

Acknowledgments

Samples were provided by the Geological Survey of South Australia. The authors thank Baohong Hou, Marc Davies, Bin Yan and Zhihong Li for their help with sample collection, as well as Yao Shi for assistance with Fe isotope analyses.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. Setting of Wilgena Hill IF in South Australia. (A) Simplified tectonic map of Australia showing major cratons, Archean, Paleo-Mesoproterozoic, Grenvillian-aged basins and orogenic belts. Image modified from [20]. (B) Regional geological map and location of the drill hole of the Wilgena Hill IF. Image modified from [21].
Figure 1. Setting of Wilgena Hill IF in South Australia. (A) Simplified tectonic map of Australia showing major cratons, Archean, Paleo-Mesoproterozoic, Grenvillian-aged basins and orogenic belts. Image modified from [20]. (B) Regional geological map and location of the drill hole of the Wilgena Hill IF. Image modified from [21].
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Figure 2. Setting and lithostratigraphy of Wilgena Hill IF in South Australia. (A) Schematic temporal evolution of major rock units of the central Gawler Craton. References for geochronology (U-Pb zircon): (1) Daly et al. [24]; (2) Fanning et al. [22]; (3) Budd [25]; (4) Reid et al. [26]. Image modified from [26]. (B) Stratigraphy of the Wilgena Hill IF in the WILDD4 drill hole. (C) Stratigraphy of the Wilgena Hill IF in the GWDD1 drill hole. (D) Stratigraphy of the Wilgena Hill IF in the HKDD4 drill hole.
Figure 2. Setting and lithostratigraphy of Wilgena Hill IF in South Australia. (A) Schematic temporal evolution of major rock units of the central Gawler Craton. References for geochronology (U-Pb zircon): (1) Daly et al. [24]; (2) Fanning et al. [22]; (3) Budd [25]; (4) Reid et al. [26]. Image modified from [26]. (B) Stratigraphy of the Wilgena Hill IF in the WILDD4 drill hole. (C) Stratigraphy of the Wilgena Hill IF in the GWDD1 drill hole. (D) Stratigraphy of the Wilgena Hill IF in the HKDD4 drill hole.
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Figure 3. Hand samples and photomicrographs of the Wilgena IF. (A) Dark- and gray-colored siltstone overlying the IF. (B) Typical banded sample with alternating hematite (gray bands) and jasper (reddish bands). (C) Reflected-light photomicrograph showing fine hematite-rich bands (light) interlayered with quartz-dominated bands (dark). (D) Plane-polarized light photomicrograph highlighting abundant jasper within the IF sample. Abbreviations are as follows: Ja = jasper, Hm = hematite, Qtz = quartz.
Figure 3. Hand samples and photomicrographs of the Wilgena IF. (A) Dark- and gray-colored siltstone overlying the IF. (B) Typical banded sample with alternating hematite (gray bands) and jasper (reddish bands). (C) Reflected-light photomicrograph showing fine hematite-rich bands (light) interlayered with quartz-dominated bands (dark). (D) Plane-polarized light photomicrograph highlighting abundant jasper within the IF sample. Abbreviations are as follows: Ja = jasper, Hm = hematite, Qtz = quartz.
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Figure 4. PAAS-normalized REE patterns for samples from the Wilgena Hill IF. Data for PAAS are taken from Taylor and McLennan [33]. (A) PAAS-normalized REE patterns for samples from the WILDD004 drill hole. (B) PAAS-normalized REE patterns for samples from the GWDD1 drill hole. Data taken from Wilkins [28]. (C) PAAS-normalized REE patterns for samples from the HKDD4 drill hole. Data taken from Wilkins [28].
Figure 4. PAAS-normalized REE patterns for samples from the Wilgena Hill IF. Data for PAAS are taken from Taylor and McLennan [33]. (A) PAAS-normalized REE patterns for samples from the WILDD004 drill hole. (B) PAAS-normalized REE patterns for samples from the GWDD1 drill hole. Data taken from Wilkins [28]. (C) PAAS-normalized REE patterns for samples from the HKDD4 drill hole. Data taken from Wilkins [28].
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Figure 5. Chemostratigraphy of the WILDD004, GWDD1, HKDD4 drill holes of the Wilgena Hill IF. Data summarize the stratigraphic changes in δ56Fe-IRMM014 and Eu/Eu*. (A) WILDD004 drillhole; (B) GWDD1 drillhole, data are taken from Wilkins [28]; (C) HKDD4 drillhole, data are taken from Wilkins [28].
Figure 5. Chemostratigraphy of the WILDD004, GWDD1, HKDD4 drill holes of the Wilgena Hill IF. Data summarize the stratigraphic changes in δ56Fe-IRMM014 and Eu/Eu*. (A) WILDD004 drillhole; (B) GWDD1 drillhole, data are taken from Wilkins [28]; (C) HKDD4 drillhole, data are taken from Wilkins [28].
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Figure 6. Relationship between δ56Fe-IRMM014 and Eu/Eu* observed in three drill holes. GWDD1 and HKDD4 drillhole date are taken from Wilkins [28]. Shale data are taken from Mclennan and Taylor [36] and Craddock and Dauphas [31]. Typical Algoma-type IF data are taken from Dauphas [37].
Figure 6. Relationship between δ56Fe-IRMM014 and Eu/Eu* observed in three drill holes. GWDD1 and HKDD4 drillhole date are taken from Wilkins [28]. Shale data are taken from Mclennan and Taylor [36] and Craddock and Dauphas [31]. Typical Algoma-type IF data are taken from Dauphas [37].
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Figure 7. Genesis model of the Wilgena Hill IF. Iron was oxidized in a suboxic state after deriving from local hydrothermal vent.
Figure 7. Genesis model of the Wilgena Hill IF. Iron was oxidized in a suboxic state after deriving from local hydrothermal vent.
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Table 1. Major and trace element compositions of the Wilgena IF from the WILDD004 drill hole.
Table 1. Major and trace element compositions of the Wilgena IF from the WILDD004 drill hole.
SampleLithologySiO2Fe2O3Al2O3LaCePrNdSmEuGdTbDyYHoErTmYbLuEu/Eu*
wt%wt%wt%μg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/gμg/g
WIL4-1Siltstone75.323.4310.0124.349.15.5219.63.80.913.380.533.05190.661.890.281.850.291.23
WIL4-4-1Ironstone28.9471.82<0.010.50.70.080.30.070.030.140.030.161.90.040.110.020.140.021.31
WIL4-4-2Jasper73.5024.99<0.010.91.20.140.60.110.050.190.030.22.70.050.140.020.150.031.78
WIL4-5Ironstone 0.810.130.50.130.050.210.040.263.50.060.180.030.20.031.41
WIL4-10-1Ironstone 0.610.120.40.090.030.150.030.172.40.040.140.020.150.031.17
WIL4-10-2Jasper 0.30.40.060.30.10.050.250.050.47.60.110.340.050.360.061.39
WIL4-16-1Ironstone31.4569.520.030.30.40.040.20.060.030.070.010.0710.020.070.010.070.012.41
WIL4-16-2Jasper79.3419.46<0.010.50.70.070.40.090.040.120.020.11.20.020.060.010.070.011.91
WIL4-22-1Ironstone 0.40.70.070.30.090.030.140.020.120.90.030.080.010.070.011.43
WIL4-22-2Jasper 0.30.50.060.30.060.040.120.020.10.80.020.060.010.060.012.35
WIL4-28-1Ironstone 0.50.90.110.50.180.080.230.040.252.10.060.180.030.190.031.91
WIL4-28-2Jasper 0.40.70.070.30.08<0.030.140.020.120.80.030.070.010.060.01
WIL4-32-1Ironstone17.9882.830.070.30.50.060.30.090.030.130.030.171.40.040.120.020.130.021.17
WIL4-32-2Jasper 0.60.80.10.40.160.050.180.020.131.30.030.070.010.070.011.66
WIL4-36-1Ironstone21.5679.520.010.50.90.090.40.10.030.160.030.172.20.040.130.020.140.021.12
WIL4-36-2Jasper77.0122.38<0.010.50.70.090.40.130.070.340.070.518.30.140.420.060.350.051.42
Table 2. Iron isotopic compositions of the Wilgena IF from the WILDD004 drill hole.
Table 2. Iron isotopic compositions of the Wilgena IF from the WILDD004 drill hole.
SampleLithologynδ56Fe (‰)2SDδ57Fe (‰)2SD
WIL4-1Siltstone20.060.000.210.06
WIL4-4-1Ironstone3−0.650.12−0.950.15
WIL4-5Ironstone2−0.600.14−0.930.17
WIL4-10-1Ironstone2−0.770.20−1.060.11
WIL4-10-2Jasper2−0.820.03−1.170.19
WIL4-16-1Ironstone2−1.420.02−2.100.04
WIL4-16-2Jasper3−1.610.03−2.300.15
WIL4-22-1Ironstone2−1.340.20−1.930.17
WIL4-22-2Jasper2−1.630.14−2.360.22
WIL4-28-1Ironstone2−0.840.06−1.220.12
WIL4-28-2Jasper2−0.730.06−1.120.21
WIL4-32-1Ironstone2−0.820.13−1.210.24
WIL4-32-2Jasper2−0.830.09−1.280.18
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Chen, S.; Sun, J.; Zhu, X.; Chen, Y. Coupled Eu Anomalies and Fe Isotopes Reveal a Hydrothermal Iron Source for Superior-Type Iron Formations: A Case Study from the Wilgena Hill Iron Formation, South Australia. Minerals 2025, 15, 824. https://doi.org/10.3390/min15080824

AMA Style

Chen S, Sun J, Zhu X, Chen Y. Coupled Eu Anomalies and Fe Isotopes Reveal a Hydrothermal Iron Source for Superior-Type Iron Formations: A Case Study from the Wilgena Hill Iron Formation, South Australia. Minerals. 2025; 15(8):824. https://doi.org/10.3390/min15080824

Chicago/Turabian Style

Chen, Shuo, Jian Sun, Xiangkun Zhu, and Yuelong Chen. 2025. "Coupled Eu Anomalies and Fe Isotopes Reveal a Hydrothermal Iron Source for Superior-Type Iron Formations: A Case Study from the Wilgena Hill Iron Formation, South Australia" Minerals 15, no. 8: 824. https://doi.org/10.3390/min15080824

APA Style

Chen, S., Sun, J., Zhu, X., & Chen, Y. (2025). Coupled Eu Anomalies and Fe Isotopes Reveal a Hydrothermal Iron Source for Superior-Type Iron Formations: A Case Study from the Wilgena Hill Iron Formation, South Australia. Minerals, 15(8), 824. https://doi.org/10.3390/min15080824

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