# Geochemical footprints of IOA and IOCG deposits in Northern Norrbotten, Sweden, and Cloncurry District, Australia

Olivier Blein, Matthieu Harlaux, Louise Corriveau, Tero Niiranen, Edward Lynch, Vladimir Lisitsin, Kathy Ehrig, Jean-François Montreuil, Blandine Gourcerol

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## To cite this version:

Olivier Blein, Matthieu Harlaux, Louise Corriveau, Tero Niiranen, Edward Lynch, et al.. Geochemical footprints of IOA and IOCG deposits in Northern Norrbotten, Sweden, and Cloncurry District, Australia. Journal of Geochemical Exploration, 2025, 277, pp.107820. 10.1016/j.gexplo.2025.107820. hal-05096974

HAL Id: hal-05096974

https://hal.science/hal-05096974v1

Submitted on 16 Jun 2025

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# Geochemical footprints of IOA and IOCG deposits in Northern Norrbotten, Sweden, and Cloncurry District, Australia

Olivier Blein<sup>a,∗</sup>, Matthieu Harlaux<sup>a</sup>, Louise Corriveau<sup>b</sup>, Tero Niiranen<sup>c</sup>, Edward P. Lynch<sup>d</sup>, Vladimir Lisitsin<sup>e</sup>, Kathy Ehrig<sup>f</sup>, Jean-François Montreuil<sup>g</sup>, Blandine Gourcerol<sup>a</sup>

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## ARTICLE INFO

### Keywords:

Metasomatism

Geochemical footprints

Albitite

Norrbotten

Cloncurry

## ABSTRACT

This paper addresses the complex hydrothermal evolution of Metasomatic Iron and Alkali-Calcic (MIAC) mineral systems based on a review of the lithogeochemical footprints of IOA and IOCG deposits in the northern Norrbotten province (Sweden) and the Cloncurry district (Australia). The use of Na-Ca-Fe-K-Mg molar barcodes on a lithogeochemical diagram tailored for these mineral systems allows to depict the evolution of MIAC systems along diagnostic metasomatic paths from high (HT) to low temperature (LT) alteration facies as follows: 1) HT or LT Na alteration (300–1000 °C); 2) HT Ca–Fe alteration (400–1000 °C); 3) HT K–Fe alteration (350–450 °C); 4) HT K and HT K-Ca-Mg alteration; 5) LT K–Fe, Na-Ca-Mg-Fe, and/or Na-Ca-Mg alteration (≤ ~350 °C); and 6) epithermal alteration (≤ 150 °C) and later stage hydrothermal veining. A distinct range of whole rock compositions and metal associations characterizes each alteration facies and can be captured by diagnostic molar barcodes and alteration indices. In northern Norrbotten, the IOA deposits are hosted in HT Ca–Fe alteration facies but regionally intensely albitized regions are overprinted by K–Fe alteration. The IOCG deposits are hosted in MIAC systems with zones of early Na (—Ca) alteration related to the regionally extensive albitite or scapolite alteration (Facies 1) and localized skarns. These are overprinted by HT Ca–Fe alteration (Facies 2) and HT to LT K–Fe alteration (Facies 3 and 5). The Cu–Au mineralization is not systematically associated with the iron oxide-rich breccias and the intense K-feldspar- or sericite-rich K–Fe alteration typical of many IOCG deposits worldwide. Instead, the lesser intensity of alteration and the abundance of mafic and ultramafic rocks in the environment lead to pattern enriched in Mg with relic of amphibole-rich alteration remaining in the assemblage as demonstrated for the Nautanen North IOCG deposit (Sweden). Consequently, the geochemical footprints of the Norrbotten Cu–Au deposits are distinct from magnetite-group (e.g., Great Bear magmatic zone, Canada) and hematite-group (e.g., Olympic Dam, Australia) IOCG deposits even if they have all the known alteration facies of MIAC systems. Conversely, IOCG deposits in northern Norrbotten show similarities to certain deposits in the Cloncurry district of Australia. In both regions, the IOCG deposits are associated with HT Ca–Fe and K–Fe alteration facies that commonly overprint early Na and/or Na–Ca alteration. In northern Norrbotten, IOA deposits are characterized by early Na alteration evolving towards Na–Ca alteration, then Fe-rich Ca–Fe alteration. These hydrothermal alteration types are subsequently superimposed by later K–Fe alteration. We conclude that the use of Na-Ca-Fe-K-Mg molar barcodes provides new insights to understand the evolution of MIAC systems and is a powerful approach for unraveling superimposed alteration trends, which can serve as an exploration targeting tool from the district- to the deposit-scale in complex metasomatized areas.

<footnote><sup>a</sup> BRGM – French Geological Survey, 45060 Orléans, France</footnote>

<footnote><sup>b</sup> Geological Survey of Canada, Natural Resources Canada, Québec City, Canada</footnote>

<footnote><sup>c</sup> Geological Survey of Finland GTK, P.O. Box 77, FI-96190 Rovaniemi, Finland</footnote>

<footnote><sup>d</sup> Division of Geosciences and Environmental Engineering, Luleå University of Technology, SE-97187 Luleå, Sweden</footnote>

<footnote><sup>e</sup> Geological Survey of Queensland, Brisbane, Australia</footnote>

<footnote><sup>f</sup> BHP-Olympic Dam, Adelaide, Australia</footnote>

<footnote><sup>g</sup> MacDonald Mines Exploration, Toronto, Canada</footnote>

<footnote>* Corresponding author.
E-mail address: o.blein@brgm.fr (O. Blein).</footnote>
# 1. Introduction

The northern Norrbotten district hosts significant Iron Oxide-Apatite (IOA) and Cu-Au deposits in northern Sweden and adjacent Finland. These include the Per Geiger, Kiruna, Malmberget, and Svappavaara IOA deposits and the Nautanen North Cu-Au Iron Oxide Copper Gold (IOCG) deposit (LKAB, 2022, 2023; Drejing-Carroll et al., 2023). Copper-gold deposits can be closely associated spatially to IOA deposits but the timing of their mineralization can differ (e.g., Gruvberget Cu deposit close to Gruvberget IOA, Tjärrojåkka Cu deposit close to Tjärrojåkka IOA deposit, Rakkurijärvi Cu-Fe deposit close to Kiruna IOA deposit; Lindskog, 2001; Edfelt et al., 2005). Other Swedish Cu-Au deposits, in addition to IOCGs, are intrusion-related and porphyry deposits (e.g., Aitik porphyry deposit; Wanhainen et al., 2003; Lundmark et al., 2005). This is in accordance with the IOCG to porphyry continuum described in Canada and global analogues (Mumin et al., 2010). Mineralization in the northern Norrbotten district occurs in at least two successive phases. The first phase, which occurred between approximately 1.89 and 1.87 Ga, formed the majority of IOA deposits and, in localized areas, some IOCG and other Cu-Au deposits. These deposits were regionally metamorphosed up to peak upper amphibolite facies conditions. The second phase, which occurred approximately between 1.80 and 1.75 Ga, is characterized by IOCG deposits and limited IOA mineralization. This stage postdates the early regional metamorphism but are themselves significantly deformed with host rocks transformed into schists and gneisses (Drejing-Carroll et al., 2023). The successive regional-scale magmatic and orogenic events in this region make it challenging to identify and characterize deposit types on a regional scale.

Building on the findings of Porter (2010), Corriveau et al. (2016, 2018, 2022a-c) have extensively researched the regional metasomatic footprint of IOCG and associated deposits. They defined the "iron oxide and alkali-calcic alteration" (IOAA) as a distinct ore system for the Fe-oxide dominant deposits. The ore system encompasses IOA, IOCG, Fe-rich Co-Au, W and Fe skarn, polymetallic K-skarn, albitite-hosted and skarn-hosted polymetallic deposits, as well as their Bi, Co, Mo, Re, REE, and U-rich variants. In these complex ore systems, the locally reduced conditions and/or the nature of the host rocks favor the genesis of deposits with Fe silicates, Fe sulfides, and Fe carbonates instead of Fe oxides (Haynes, 2000; Skirrow, 2022; Hamilton et al., 2023). In addition, when fluids evolve to an Fe-poor composition, or when subsequent remobilization occurs in the systems, Fe-poor metasomatites and deposits form, including five-element veins (Corriveau et al., 2022c). To encompass all deposit types, the term "Metasomatic Iron and Alkali-Calcic" (MIAC) mineral systems was introduced by Corriveau et al. (2022c), whether Fe-oxide-enriched or not, and Fe-rich or not (Montreuil et al., 2015; Hofstra et al., 2021; Corriveau et al., 2022c; Hamilton et al., 2023). Furthermore, deposits of MIAC systems frequently include several types of mineralization, resulting in significant overprinting.

Consequently, mineral exploration and mining companies need to identify methods to improve exploration targeting by efficiently processing readily available information, including lithogeochemical datasets from geological surveys, academic institutions, corporate databases, and industry assessment reports. Here, we expand on Niiranen et al. (2019) by illustrating how geochemical discriminant diagrams and techniques for visualizing alteration types can help recognize and interpret available data from deposit to regional scale for IOCG and affiliated critical mineral deposits. As previously stated by Niiranen et al. (2019), this work highlights the necessity for an effective mineral system model in conjunction with an understanding of the metasomatic evolution of host rocks in order to optimize the interpretation of potential deposit types at the regional scale.

Given the considerable diversity observed in the composition of deposits and associated alteration zones in MIAC systems, whole-rock geochemical analyses can be used to elucidate the alteration patterns observed at the deposit to province scale. The use of molar proportions

of metasomatically mobile major elements, such as Na-Ca-Fe-K-Mg, enables the quantification of bulk chemical changes related to metasomatism. The use of Na-Ca-Fe-K-Mg molar barcodes on the discriminant diagram for IOCG (i.e., the AIOCG diagram; Montreuil et al., 2013) is an effective proxy for identifying the types, intensity, and overprints of alteration in mineralized zones.

This contribution summarizes the geochemical footprints of IOA, IOCG, and Cu-Au deposits in the northern Norrbotten province, Sweden which formed in a dominantly volcano-plutonic setting with abundant mafic to intermediate rock types and subordinate sedimentary rocks prior to and coevally with the emplacement of granitic intrusions (Martinsson et al., 2016; Veress et al., 2024). The presence of evaporite units is inferred based on the large-scale scapolite alteration in the region as well as by rare pseudomorphing of potential evaporite beds (Martinsson et al., 2016). The Norrbotten geochemical footprints are then compared with that of other well-studied MIAC systems and deposits around the world. The MIAC systems of the Norrbotten district in Sweden, the Great Bear magmatic zone (GBMZ) in Canada, and the Olympic Dam deposit in Australia formed in volcano-plutonic settings with abundant intermediate to felsic rock types and subordinate sedimentary rocks, largely prior to the emplacement of a granitic batholith (Corriveau et al., 2022a). Those of the Cloncurry district in Australia formed dominantly within sedimentary sequences with evaporite units prior to and coevally with emplacement of a granitic batholith (Mark et al., 2006; Cave et al., 2024). The Norrbotten and Cloncurry districts show similarities of metasomatic compositional trends, which are distinct from that of the GBMZ and the Olympic Dam deposit. The difference in lithogeochemical footprints is essentially due to the extent to which the Ca-Fe and K-Fe alteration facies have overprinted and replaced earlier formed albitite and the host sequence that is commonly rich in mafic and ultramafic rocks. The research also provides insights into the additional ore deposition that occurs in MIAC systems through the remobilization of primary metal endowment and the addition of new metals. This enables a more comprehensive understanding of the long-term mineralization events that characterize MIAC metallogenic provinces.

# 2. Alteration footprints of MIAC mineral systems

## 2.1. Alteration facies

The MIAC mineral systems are fluid-driven systems triggered by the accumulation, ascent and lateral propagation of voluminous and extremely hot (up to 1000 °C) hypersaline fluid plumes and associated salt melts (Li et al., 2015; Bain et al., 2020; Xu et al., 2024a,Xu et al., 2024b; Zhao et al., 2024). These processes occur on a regional scale, covering 500 km² for example (Corriveau et al., 2022a). Metasomatism induces mineralogical, chemical and textural transformations of the upper crust along extensive metallogenic belts (Sillitoe, 2003; Corriveau et al., 2022d and papers therein; Xu et al., 2024a,Xu et al., 2024b). As infiltration metasomatism progresses from depth to surface and propagates along and across major fault zones and other discontinuities, the physicochemical conditions of the fluid plumes driving the system evolve over time (Williams, 2010; Ootes et al., 2010; Kelly et al., 2020; Corriveau et al., 2022a). Consequently, a sequence of distinct mineral assemblages is precipitated and can be described by a series of Fe-rich to Fe-poor, alkaline (Na, K) and alkaline-earth (Ca, Mg) alteration facies. At each stage, or alteration facies, the elements and metals that can be precipitated are determined by the stable mineral assemblages, themselves controlled by the physicochemical conditions of the fluid plume (Corriveau et al., 2022a-c). The sequence of alteration facies defines a prograde metasomatic pathway (Corriveau et al., 2010a, 2010b, 2016, 2022a-c).

Over time and around the world, we can observe that MIAC facies and their deposit types vary between high to low temperatures (HT to LT), and are as follows (see Corriveau et al., 2022c and references
therein for details):

* Facies 1 is characterized by early, intense and pervasive Na (—Ca) alteration (albite, scapolite) forming corridors of albitite and intense albitization or scapolatilisation on a regional scale along fault zones, intrusive contacts and stratigraphic discontinuities.

* Facies 2 is defined by HT Ca-Fe alteration associated with amphibole- to magnetite-dominant, ± apatite, clinopyroxene, and epidote assemblages, which can give rise to Fe (magnetite) skarn deposits, IOA deposits (e.g., Kiruna, Sweden) with Fe-P (e.g., Malmberget, Sweden), Fe-REE (e.g., Per Geiger, Sweden) or Ni (e.g., Jaguar, Brazil) resources, and skarn-hosted REE deposits (e.g., Bastnäs, Sweden).

* Facies 3 is characterized by the formation of HT K-Fe alteration assemblages containing K-feldspar, biotite, and magnetite. These assemblages are associated with IOCG deposits (e.g., Ernest-Henry, Australia, Nautanen North, Sweden), iron sulfide copper-gold deposits (ISCG; e.g., Eloise, Australia) and Fe oxide-U deposits.

* Facies 4 is defined by the presence of barren HT K-felsite (K-feldspar dominant metasomatite) in silicic host rocks. This facies can be observed as halos along IOCG breccias, as well as in K-skarns (clinoopyroxene, garnet, K-feldspar).

* Facies 5 corresponds to LT K-Fe to Na-, Ca-, Mg- or Si-Fe alterations (hematite, muscovite, chlorite, carbonate, locally albite) which occur in IOCG (e.g., Olympic Dam, Australia), ISCG, and Fe oxide-U deposits as well as a large variety of Fe-silicate, Fe sulfide and Fe-rich carbonate deposits with Ag, Au, Cu, U, LREE and Th resources (e.g., Scadding Au, Canada).

* Facies 6 includes phyllic, sericitic, advanced argillic alteration and associated mineralization (e.g., Echo Bay Gossan, Canada) as well as the many generations of mineralized veins that formed during and after the development of the primary MIAC system (Gandhi et al., 2018; Ehrig et al., 2021; Corriveau et al., 2022a-c; Cave et al., 2024; Somarin et al., 2024).

Alteration facies, which comprise a suite of mineral assemblages, geochemical signatures, metal associations, and genetically related deposits, represent the main components of MIAC systems and serve as key vectors for ore exploration at both the province and deposit scales (Corriveau et al., 2010a, 2016, 2022a-d; Day et al., 2016; Montreuil, 2016; Montreuil et al., 2016a, Montreuil et al., 2016b; Blein et al., 2022; Chen and Zhao, 2022; Zhao et al., 2022; Drejing-Carroll et al., 2023; Hamilton et al., 2023).

## 2.2. Geochemical tools

Whole-rock geochemical data can be used to track metasomatic evolution in MIAC mineral systems. Intensive alteration results in a notable change in major element composition (Montreuil et al., 2016; Blein et al., 2022; Corriveau et al., 2022b). Sodium, Ca, K, Fe, and Mg molar proportions of alteration facies 1 to 5 exhibit distinctive variations according to alteration types, intensity, and overprinting, as well as to a lesser degree, host rock composition. In cases of intense alteration, the molar proportions of the metasomatites differ significantly from those in least-altered sedimentary, igneous, and metamorphic rocks. These distinctive proportions can be visualized using diagnostic Na-Ca-K-Fe-Mg molar barcodes derived from whole-rock geochemical data. Barcodes with balanced proportions of these cations are found in the least-altered samples. Metasomatized rocks, on the other hand, show barcodes with one or two dominant cations. Their distinctive associations serve as proxies for the characteristic minerals that discriminate alteration facies (Fig. 1). The barcodes can be plotted on regional to deposit-scale maps and along drill cores to visualize the spatial distribution of alteration facies (Montreuil et al., 2016b), or on discriminating

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** A: Diagnostic Na-Ca-Fe-K-Mg molar barcodes of metasomatites used in the geochemical plots (data from Corriveau et al., 2015; figure modified from Blein et al., 2022 and Corriveau et al., 2022b). B: Na-Ca-Fe-K-Mg molar barcodes of metasomatic minerals from the GBMZ (Sidor, 2000) on the AIOCG diagram of Montreuil et al. (2013).</figcaption></figure>
geochemical diagrams such as the AIOCG diagram of Montreuil et al. (2013) for MIAC systems (Fig. 2; Day et al., 2016; Acosta-Góngora et al., 2022; Corriveau et al., 2022b; Drejing-Carroll et al., 2023).

## 2.3. Metasomatic paths

The metasomatic paths of MIAC systems on AIOCG diagrams and the barcode signatures of the main alteration facies and their common overprints have been documented in Acosta-Góngora et al. (2022), Blein et al. (2022), Corriveau et al. (2022b), and Drejing-Carroll et al. (2023). The following section describes and explains the metasomatic paths of well-studied MIAC systems.

Fig. 2A-B illustrates the metasomatic path of the altered Roxby Downs Granite (RDG) of the Hiltaba Suite in boreholes outside (RD2499) and inside (RD2715) of the Olympic Dam Breccia Complex (ODBC). Outside the ODBC, from its contact to >5 km, the surrounding granitoids are characterized by pervasive sericitization, which defines a sub-vertical path between the least-altered field and the K ± Fe alteration field (Fig. 2A; see also Blein et al., 2022). The alteration of the RDG from the outer part to the core of the ODBC defines a clockwise metasomatic path from the least-altered field to the sericite-rich K alteration field towards the Fe-rich alteration fields (Fig. 2B). Within the ODBC, hematite alteration intensifies, including widespread replacement of earlier granitic fragments and matrix. The metasomatic path is characterized by increasing molar proportions of Fe. Firstly, altered samples migrate horizontally from the sericite-rich pole of the K alteration fields towards the K-Fe and Fe-rich K-Fe alteration fields (Fig. 2B). Secondly, samples with the highest degree of alteration migrate diagonally

towards the Fe-rich Ca-K-Fe and Fe-rich Ca-Fe alteration fields. This is due to the concomitant decrease in Na-Ca content and increase in Fe content induced by the intensifying hematite alteration of the granitic clasts within the breccia complex (Fig. 2B).

Fig. 2C illustrates the metasomatic path of the GBMZ in Canada's Northwest Territories. Samples with low to moderate alteration were removed from the dataset to best discriminate the signature of each alteration facies and their deposit types. The metasomatized host rocks comprise clastic or carbonate sedimentary rocks and calc-alkaline to shoshonitic mafic to felsic igneous rocks. The high intensity alteration of the samples has removed the impact of the protolith compositional signature on the metasomatite composition. The altered samples define a counter-clockwise prograde metasomatic path across the Na, Na-Ca-Fe, Ca-Fe, Ca-K-Fe, K-Fe, K, and Fe-rich fields (Fig. 2C). In the initial stages of metasomatism, the most altered samples exhibit a horizontal migration from the Na, Na-Ca-Fe, Ca-Fe, and Fe-rich Ca-Fe fields (Fig. 2C). Following the HT Ca-Fe alteration, the highly altered samples migrate vertically and diagonally from the Fe-rich Ca-Fe field into the Fe-rich Ca-K-Fe, Ca-K-Fe, K-Fe, and K fields (Fig. 2C). The migration to the K field is towards K-feldspar instead of the muscovite field that is observed in the Olympic Dam dataset. Samples with LT K-Fe alteration also plot in the K-Fe alteration field. In general, LT K-Fe alteration facies are distinguished by a higher AIOCG 1 index than that observed in HT K-Fe alteration facies. As observed in the ODBC, the metasomatic path from the K alteration field to the LT K-Fe alteration is sub-horizontal but extends into the Fe-rich K-Fe field (Fig. 2C) before migrating to the Fe-rich Ca-Fe field through pervasive hematite alteration with and without fluorite (higher Ca contents).

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Evolution of prograde metasomatic paths in the Olympic Dam (A: borehole RD2499 outside of the ODBC; B: borehole RD2715 inside of the ODBC) and Great Bear magmatic zone (C) deposits, modified from Blein et al. (2022). Data: Corriveau et al. (2015), and BHP Olympic Dam (unpublished data; boreholes RD2499 and RD2715). Blue trend: most intense alteration. Yellow trend: least to most altered trends; (D) Theoretical metasomatic trends from least altered to most altered rocks (yellow trends), and from alb itite to intense overprinting by a distinct alteration facies (white trends) with typical barcodes of endmember alteration facies. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>
In summary, the degree of alteration of the host rocks and the type of minerals and the mineral contents of that alteration defines the alteration paths, which range from a weakly altered pole in the least-altered field to a metasomatic pole. Alteration overprints define paths from the field of each alteration facies and can be recognized by having atypical cationic proportions (Acosta-Góngora et al., 2022; Blein et al., 2022; Corriveau et al., 2022b). Such trends involve the mixing of two components (e.g., host rock vs hydrothermal alteration), which may result in the sample composition transecting several fields (Fig. 2D). The transitional fields do not necessarily reflect the alteration undergone by the sample due to the mixing of the varied components. This caveat can be mitigated by avoiding plotting samples as dots on the diagram and instead plotting the barcodes. For example, the overprinting of albitite

by Ca-Fe, Ca-K-Fe, K-Fe, or K alteration results in alteration trends that transect the field of least altered samples. However, these trends exhibit very atypical molar barcodes relative to least altered rocks which enables the identification of superimposed alteration facies (Fig. 2D; Corriveau et al., 2022b; Blein et al., 2023; this work).

### 3. Geological context

#### 3.1. Northern Norrbotten district, Sweden

In northern Norrbotten (Fig. 3), the bedrock geology is dominated by Paleoproterozoic supracrustal and plutonic rocks that were emplaced on the Archean Norrbotten craton. The geological evolution includes

<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Simplified geological map and location of major IOA, IOCG-style and related ore deposits in the northern Norrbotten province (Sweden and Finland).</figcaption></figure>
episodes of rifting followed by subduction and accretionary events (Martinsson, 2004; Weihed et al., 2005; Billström et al., 2010). The Archean basement is composed of meta-granitoids emplaced at ca. 2.8 Ga, and subsequently metamorphosed at 2.7 Ga (Martinsson et al., 1999; Bergman et al., 2001). These rocks are overlain by 2.50–1.96 Ga mafic-ultramafic intrusions and supracrustal rocks, collectively known as the Kiruna Greenstone and Kovo groups (Martinsson, 1997). These mafic to ultramafic intrusions are linked to a plume-driven continental uplift that resulted in continental rifting (Bergman et al., 2001; Lahtinen et al., 2008).

During the Paleoproterozoic, oceanic subduction was initiated at ca. 1.95 Ga beneath the Norrbotten micro-continent (Öhlander et al., 1993; Wanhainen et al., 2006; Martinsson et al., 2016). To the north of the Skellefte district, this led to the formation of ca. 1.89–1.86 Ga calc-alkaline magmatism in well-defined intra-arc to back-arc basins (Wanhainen et al., 2006; Martinsson et al., 2016; Andersson et al., 2021). This subduction-related arc activity was short-lived and ceased at ca. 1.88 Ga (Cliff et al., 1990; Romer et al., 1994). In the Kiruna area, the transition from calc-alkaline to shoshonitic magmatism is interpreted as a transition from a compressive subduction context to an extensional one (Martinsson and Perdahl, 1995). Magmatic suites dated to 1.90–1.86 Ga represent the early Svecokarelian cycle, which is followed by the late-orogenic Svecokarelian phase (1.81–1.78 Ga) producing I- and A-type plutonic rocks, which are locally associated with S-type granites (Andersson, 1991; Åhäll and Larson, 2000; Weihed et al., 2002; Högdahl et al., 2004; Rutanen and Andersson, 2009).

Northern Norrbotten represents a significant metallogenic province, which is identified by the occurrence of numerous Fe- and Cu ± Au deposits. This province extends eastward to the Kuusamo belt in Finland (Juomasuo Co-Au-REE and Hangaslampi Au—Co deposits; Martinsson et al., 2016; Vasilopoulos et al., 2021; Weis et al., 2022). The district has been considered as a prototypical example of an IOCG province due to its mineral deposits and regionally developed albite and scapolite alteration (e.g., Martinsson, 2001; Williams et al., 2003). Kiruna-type IOA deposits are primarily concentrated in the Kiruna and Gällivare regions and are spatially correlated with the Kiirunavaara Group, a 1.90–1.87 Ga package of mainly intermediate to felsic volcanic rocks. Orogenic Cu—Au deposits, partly of the IOCG type, are hosted by the Karelian greenstones and in Svecofennian volcanic rocks. These deposits formed through the reactivation of MIAC systems, which are located along fault zones and the remobilization of their primary metal endowment (Bergman et al., 2001; Bauer et al., 2022; Bauer and Andersson, 2023). The IOA and IOCG deposits in northern Sweden and adjacent parts of Finland were formed during the evolution of a Paleoproterozoic continental margin arc from ca. 1.90 to 1.75 Ga (Juhlin et al., 2002). In many respects, the age, tectonic context, and metallogenic features of these deposits are comparable to those of the GBMZ in Canada (Montreuil et al., 2016a; Ootes et al., 2017). These two MIAC provinces formed during the Paleoproterozoic in a continental active margin context, with an association of IOA and IOCG deposits, and albitization prior to IOA-type mineralization. However, the degree of scapolite alteration in the Norrbotten district and potential evaporitic host rocks (Martinsson et al., 2016) have no equal in the Great Bear magmatic zone (Corriveau et al., 2022a).

## 3.2. Cloncurry district, Australia

In northwest Queensland, the Mount Isa inlier is a polyphase fold belt divided into three N-S-trending tectonostratigraphic domains (Fig. 4; Hatton and Davidson, 2004). The Eastern fold belt is renowned for its plethora of IOCG, ISCG, and other MIAC-related Cu-Pb-Zn and critical metals deposits in the Selwyn-Mount Dore corridor. These include the Ernest-Henry, Mount Elliott/SWAN (South West magnetic ANomaly), Monakoff, Osborne, Starra, and the E1-Group Cu—Au IOCG deposits, the Rocklands Cu-Co-Au IOCG deposit, the Eloise Cu—Au ISCG deposit, and the Mount Dore Cu-Au-Pb-Zn, Merlin Mo—Re, and Tick Hill Au low-Fe

deposits.

The Eastern fold belt is dominated by sedimentary and volcanic rocks deposited in intracontinental extensional basins between 1.78 and 1.61 Ga (Page and Sun, 1998; Jackson et al., 2000; Giles and Nutman, 2002). These rocks have been deformed during several tectonic events between 1.63 and 1.51 Ga, with metamorphism at 1.58 Ga (Giles and Nutman, 2002, 2003), and intruded by granites at 1.74 Ga, 1.63 Ga, and 1.55–1.50 Ga (Page and Sun, 1998).

Within the Selwyn-Mount Dore corridor, the IOCG deposits are located in bimodal volcanic and sedimentary rocks (the Soldiers Cap Group and the Staveley Formation). These volcano-sedimentary sequences were deposited during two periods of rifting between ca. 1.77–1.71 Ga (Cover Sequence 2) and ca. 1.69–1.65 Ga (Cover Sequence 3), respectively (Sun, 1998; Giles and Nutman, 2003). The Soldiers Cap Group is composed of two major units: i) a lower unit with metapelite, quartzite, and metabasalt; and ii) an upper unit dominated by metabasalt, with quartzite and metapelite. The Staveley Formation is composed of intercalated calcareous metasiltstone, metasandstone, and metabasalt (Beardsmore et al., 1988). The presence of evaporitic units is inferred to be widespread based on the extensiveness of scapolite alteration (Morrissey and Tomkins, 2020).

# 4. MIAC-related deposits in Norrbotten and Cloncurry districts

## 4.1. Northern Norrbotten district

In northern Norrbotten, MIAC systems and their IOA deposits (mainly Kiirunavaara and Malmberget) formed in intracontinental arc basins and replaced co-magmatic calc-alkaline to shoshonitic volcanic and plutonic rocks at ca. 1.90–1.85 Ga (Martinsson et al., 2016; Sarlus et al., 2020; Andersson et al., 2021). Subsequently, Cu—Au and epige netic Au deposits formed during crustal shortening and are located in basin inversion structures (Andersson et al., 2021; Andersson et al., 2022). Those containing Fe oxides were assigned to IOCGs, including the Nautanen and Nautanen North deposits (Andersson et al., 2021; Bauer et al., 2022; Drejing-Carroll et al., 2023; Melfou et al., 2023). The northern Norrbotten district also includes Fe skarn, stratiform- stratabound Cu—Zn, and banded iron formations that formed at ca. 2.1 Ga (Billström et al., 2010). Some IOCG-type deposits are also present in the Pajala-Kolari region, situated across the border between Sweden and Finland (Niiranen et al., 2007). Furthermore, albitite-hosted Co—Au deposits are situated to the east in the Kuusamo belt of Finland (Rasilainen et al., 2020).

A temporal gap of ca. 60 Ma between IOA deposits and some of the IOCG deposits and variants thereof within the Norrbotten province has been proposed (Billström et al., 2010; Martinsson et al., 2016; Bauer et al., 2022; Logan et al., 2022; Bauer and Andersson, 2023). The majority of IOA deposits were formed essentially between 1.89 and 1.87 Ga (Cliff et al., 1990; Romer et al., 1994; Martinsson et al., 2016; Westhues et al., 2016; Bauer et al., 2018). The IOCG deposits were formed in two distinct phases. While some of the IOCG deposits may have the same age as the IOA deposits, most appear to be significantly younger, exhibiting a structural link to the late Svecokarelian phase (1.79–1.81 Ga; Bauer et al., 2022; Andersson et al., 2021; Drejing-Carroll et al., 2023).

### 4.1.1. Kiruna district

The supracrustal rocks of the Kiruna mining district host a wide range of deposit types: i) IOA deposits (Kiirunavaara, Luossavaara, Tjårrojåkka-Fe, Gruvberget-Fe); ii) Cu—Au deposits and orogenic gold deposits characterized by an atypical metal association (Pahtohavare); iii) proposed stratiform-stratabound exhalative Cu-(Fe—Zn) deposits (Viscaria); and iv) IOCG deposits (Rakkurijärvi, Tjårrojåkka-Cu, Pik- kujärvi, Nautanen, Gruvberget-Cu). The oldest IOCG deposits (Rakkur- ijärvi and Pikkujärvi) were formed between 1.89 and 1.86 Ga (Wanhainen et al., 2006; Smith et al., 2007), and the youngest deposits (Tjårrojåkka-Cu and Gruvberget-Cu) were formed between 1.80 and
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Simplified regional geologic map of the Eastern fold belt of the Mount Isa inlier, northwest Queensland, Australia, showing the location of major IOCG-style deposits.</figcaption></figure>
1.75 Ga (Edfelt, 2007). Locally, the IOA deposits were synchronous with the younger phase of the IOCG-forming event, as evidenced by the Tjärrojåkka Fe deposit (Edfelt, 2007).

The Kiirunavaara IOA deposit is 5 km long and up to 100 m thick. It is located at the contact between the Luossavaara (hanging wall) and Hoppuka (footwall) volcanic formations. The emplacement of the Kiirunavaarana deposit is contemporaneous with syn-volcanic faulting during the initial stages of basin development (Andersson et al., 2022). The host rocks surrounding the deposit are characterized by the presence of actinolite, albite, biotite, and scapolite alteration assemblages (Bergman et al., 2001; Barton, 2014).

The Rakkurijärvi IOCG deposit, located SW of Kirunavaara (Fig. 3), is associated within a NE-SW-trending shear zone (Smith et al., 2007). It occurs in the Kurravaara conglomerate and in volcanic rocks of the Kiirunavaara Group (Smith et al., 2010). Host rocks have undergone alteration to the Na-(Ca) (albite, scapolite), HT Ca—Fe (magnetite, actinolite), HT Ca-K-Fe (biotite, actinolite, K-feldspar), and HT K—Fe (magnetite, biotite, K-feldspar), and Cu-mineralized LT K—Fe to Ca-Mg-Fe (e.g., hematite, chlorite, carbonate) facies (Smith et al., 2007). Chalcopyrite is the main ore-forming sulfide, precipitating within the matrix of lithic fragment breccias and massive magnetite breccia (Smith et al., 2007).

### 4.1.2. Gällivare district

The Gällivare area hosts significant mineral deposits, such as the Malmberget IOA deposit, the Nautanen and Nautanen North IOCG deposits, and the Aitik porphyry Cu—Au deposit. The Malmberget IOA deposit is comprised of a series of Fe-oxide orebodies distributed along a 5-km-long trend (Bauer et al., 2018). These deposits consist of massive, brecciated, and layered bodies containing magnetite- and/or hematite with apatite, amphibole, pyroxene, biotite and minor sulfides (Lund, 2013). Mineralization formed prior to a regional deformation, with a penetrative foliation, dated at ca. 1.88 to 1.87 Ga. Iron oxide orebodies are spatially associated with albitized rocks (Bauer et al., 2018).

Interpreted as a Paleoproterozoic metamorphosed porphyry deposit (ca. 1.9 Ga), the Aitik Cu-Au-Ag-(Mo) deposit was affected by a regional IOCG-type hydrothermal event at ca. 1.8 Ga (Wanhainen et al., 2012). The Aitik area is composed of Paleoproterozoic schists and gneisses, mafic to intermediate intrusions, and dykes (Wanhainen and Martinsson, 1999; Wanhainen et al., 2005). The rocks of the footwall and ore zones consist of sericitized quartz-muscovite schists and gneisses, and garnet-biotite and biotite-amphibole-feldspar schists. These facies are the consequence of hydrothermal alteration affecting a quartz monzodiorite and the related volcaniclastic mafic to intermediate rocks recrystallized to biotite-amphibole-feldspar gneisses (Wanhainen et al., 2014). To the west, the hanging wall is composed of barren amphibole-biotite-feldspar gneisses and amphibolites (Wanhainen et al., 2014). A saline mineralizing fluid formed vein-type and disseminated ore of pyrite and chalcopyrite within volcaniclastic rocks, and caused potassic alteration (biotite, K-feldspar) of the host rocks (Wanhainen et al., 2012).

Within the Nautanen deformation zone, the Nautanen deposit lies close to the Malmberget IOA and Aitik porphyry Cu—Au deposits. Hydrothermal alteration and mineralization with clear IOCG affinities characterize the Nautanen deposit (Lynch et al., 2018). The host deformation zone, 3 km wide, is a NNW-trending tectonic structure with highly schistose or mylonitic rocks (Lynch et al., 2018). The Nautanen deposit occurs in sheared quartz veins (Edblom, 2020). It is associated with K-feldspar-epidote alteration, tourmalinization, and sericitization (Martinsson and Wanhainen, 2004). The initial phase of metasomatism was characterized by significant Na (—Ca) alteration, with extensive scapolite observed at Nautanen (Martinsson and Wanhainen, 2004; Martinsson et al., 2016; Edblom, 2020). This alteration was subsequently overprinted by an assemblage of minerals, including amphibole-K-feldspar-biotite-magnetite, ± pyrite, ± chalcopyrite, forming the mineralized zones (Edblom, 2020; Melfou et al., 2023). A late-stage

alteration with epidote ± quartz ± carbonate commonly overprints hematized albite and albitized rocks (Lynch et al., 2018). Early magnetite, sodic alteration and later potassic and carbonate alteration are spatially associated with the occurrence of chalcopyrite mineralization (Edblom, 2020; Melfou et al., 2023). However, the development of major Cu-mineralization is paragenetically later than that of magnetite (Edblom, 2020; Melfou et al., 2023).

The Nautanen North deposit also formed within the Nautanen shear zone and is the largest IOCG deposit of the Norrbotten district (Drejing-Carroll et al., 2023). The deposit consists of deformed and metamorphosed metasomatites now forming a variety of amphibole-dominant to biotite-rich to sericite-rich schists and gneisses. Parageneses evolved from early Facies 1 Na and Facies 1–2 Na-Ca-Fe through to Facies 2 HT Ca—Fe and Facies 2–3 HT Ca-K-Fe to Facies 3 and 5 HT K—Fe and LT K—Fe alteration. The latter two host the sulfide mineralization (Drejing-Carroll et al., 2023).

### 4.1.3. Pajala-Kolari district

The majority of Cu—Au deposits within the Pajala-Kolari district are located within or near fault zones that collectively form the complex N-to NNE-trending Pajala shear zone (Väisänen, 2002). A distinctive attribute of the country rocks is the pervasive presence of albitization, which has been documented in numerous locations along the Pajala shear zone (Lahtinen et al., 2015).

The Pajala area of Sweden is characterized by the presence of a number of different types of Fe skarn. The largest of these is the Stora Sahavaara deposit. It consists of three lenses of Fe-rich skarn at the contact between quartzite (hanging wall) and volcaniclastic rocks (footwall; Lundberg, 1967). The ore zone, up to 80 m thick, consists of serpentine-rich magnetite ore within a serpentine-diopside-tremolite skarn (Lundberg, 1967). Three principal stages of alteration were observed within the deposit (Abongwa, 2009). Early Na alteration (albite, scapolite) occurs at the regional scale and has affected graphitic phyllites and mafic volcanic rocks (footwall; Martinsson and Perdahl, 1995) and tuffites (hanging wall; Abongwa, 2009). The Fe (magnetite) mineralization precipitated at the HT Ca—Fe facies with pyrite and pyrrhotite, and overprinted the early skarn, as evidenced by the presence of relics of clinopyroxene-tremolite assemblages, which were subsequently replaced by LT Mg serpentine alteration (Niiranen, 2011). The Tapuli deposit occurs as an irregularly shaped orebody, measuring 350 m in width, of magnetite-bearing skarn within a thick dolomite unit, intercalated between graphitic, and partly sulfide-rich, phyllite in the footwall and quartzitic phyllite in the hanging wall (Hanski and Huhma, 2005; Eilu, 2012). Magnetite forms irregular bands, veins, and blebs, in addition to trace amounts of pyrite, pyrrhotite, and chalcopyrite (Lindroos et al., 1972). Four main stages of alteration were described (Niiranen, 2011). Early Na alteration (albite, scapolite) occurs regionally. Fe mineralization occurs at the HT Ca—Fe facies (magnetite-actinolite) after the development of an early skarn assemblage (clinopyroxene-tremolite) and was subsequently overprinted by LT Mg serpentine alteration (Niiranen, 2011).

In the Kolari district (Finland), the Hannukainen deposit (1.8 Ga) is composed of massive magnetite-rich lenses embedded in skarn (Hiltunen, 1982; Moilanen and Peltonen, 2015). In distal zones, the alteration assemblage is composed of albite and scapolite (Moilanen and Peltonen, 2015). In the intermediate zones, the dominant alteration minerals are biotite and K-feldspar. In the proximal alteration zone, which surrounds the magnetite bodies, clinopyroxene is present with variable amounts of magnetite, amphibole, and calcite (Hiltunen, 1982; Moilanen and Peltonen, 2015). The Kuervitikko deposit, situated ca. 5 km to the north of Hannukainen, comprises extensive to semi-massive skarn-hosted magnetite lenses as well as breccia-hosted parts (Niiranen et al., 2007). Magnetite, pyrite, pyrrhotite, and chalcopyrite brecciated intensely albitized country rocks and granitic pegmatites (Niiranen et al., 2007). The footwall of this deposit is composed of albitized mafic metavolcanic rocks, micaceous gneisses, and quartzites
(Niiranen et al., 2007). The hanging wall is comprised of albitized dio-
rite and monzonite. In the Cu-Rautuvaara deposit, Cu—Au ore is hosted
by albitite with disseminated magnetite, anthophyllite, and biotite
(Niiranen et al., 2007). This forms a 45-m-thick, elongated lens.
Furthermore, the occurrence of clinopyroxene-amphibole skarn and
ironstone lenses, analogous to those observed at Laurinoja and Kuervi-
tikko (Niiranen et al., 2007), is also noted. As in Laurinoja and Kuervi-
tikko, the hanging wall is composed of monzonite and diorite, with
albitized mafic metavolcanic rocks forming the immediate footwall
(Niiranen et al., 2007).

## 4.2. Cloncurry district

The geochronological studies have revealed that two distinct epi-
sodes of Cu—Au mineralization are associated with discrete orogenic
events, occurring at around 1.60 Ga and between 1.55 and 1.50 Ga,
respectively (Baker et al., 2001; Gauthier et al., 2001; Oliver et al., 2004,
2008; Betts et al., 2006; Rubenach et al., 2008; Duncan et al., 2011,
2014). The initial poorly defined episode is associated with the peak
metamorphism during the Isan orogeny between ~1.60 and 1.57 Ga (e.
g., some interpretations of the timing of the Osborne and Starra deposits;
Duncan et al., 2014), and the second widespread episode of Cu—Au
mineralization is broadly contemporary with the Williams-Nakaru
batholiths between 1.55 and 1.50 Ga (e.g., Eloise, Ernest-Henry,
Mount Dore deposits, and Mount Elliott/SWAN; Mark et al., 2006;
Duncan et al., 2011). A number of IOCG, ISCG, and low-Fe deposits in
the region, including the Ernest-Henry IOCG deposit, are composed of
structurally controlled Fe-oxide breccias. In contrast, other deposits
occur as stratabound replacement zones (e.g., El deposits and the
ironstones at Starra; Williams, 1994; Case et al., 2017). All deposits
exhibit a similar paragenetic sequence of hydrothermal events,
including the following: i) early Na and Na—Ca alteration; ii) HT Ca—Fe
alteration; iii) HT K—Fe alteration with Cu—Au mineralization (most
pronounced at the Ernest-Henry deposit); and iv) mineralized LT Ca—Fe
alteration with carbonate and magnetite (Mark et al., 2006; Corriveau
et al., 2010b, 2022a; Duncan et al., 2014; Hohl et al., 2024). The relative
intensity of these alteration types exhibits significant variation between
different MIAC Cu—Au deposits in the Cloncurry district. Skarn assem-
blages are observed only in few deposits (e.g., Mount Elliott/SWAN,
Brown et al., 2009; Duncan et al., 2014).

4.2.1. *Ernest-Henry deposit*

The Ernest-Henry deposit is the largest IOCG deposit in the Cloncurry
district (166 Mt. at 1.1 % Cu, 0.54 g/t Au; Lilly et al., 2017; Current: 88.3
Mt. at 1.28 % Cu, 0.73 g/t Au; Evolution Mining, 2022). The deposit is
hosted by Paleoproterozoic meta-andesitic to dacitic lavas with minor
basaltic rocks (ca. 1.74 Ga; Page and Sun, 1998). The initial poorly
defined episode is associated with the peak metamorphism during the
Isan orogeny between ~1.60 and 1.57 Ga (Craske, 1995; Cave et al.,
2018). The ore zone is composed of magnetite-K-feldspar-chalcopyrite
±biotite and magnetite-carbonate-chalcopyrite assemblages, which
occur primarily as the matrix of a volcanic clast-supported breccia (Mark
et al., 2006; Cave et al., 2018; Corriveau et al., 2022a). At Ernest-Henry,
mineralization occurred at ca. 1.53 Ga associated with A-type granitoids
of the Williams-Naraku suite (Belousova et al., 2001; Mark et al., 2006;
Cave et al., 2018). The host rocks surrounding the Ernest-Henry deposit
have been affected by three main phases of hydrothermal alteration: i)
pre-ore Na and Na—Ca alteration; ii) pre-ore HT Ca-Fe; to iii) syn-ore HT
K—Fe and LT Ca—Fe alteration with Cu—Au mineralization (Mark et al.,
2006; Corriveau et al., 2010b, 2022a). The Na—Ca alteration is exten-
sive along NE-trending shear zones. The HT K—Fe alteration, which is
characterized by magnetite-amphibole-biotite-K-feldspar-garnet and
carbonate-rich veins and minor breccias, is localized within a kilometer-
long extension around the orebody. The HT K—Fe alteration and Cu—Au
mineralization stage is characterized by the development of extensive
potassic K-feldspar dominant alteration of the breccia fragments and of

the host rocks, which is most intense near the ore zone (Mark et al.,
2006).

4.2.2. SWAN deposit

Within the Eastern Fold belt, the SWAN deposit, a large, low-grade
Fe-Cu-Au deposit (353.7 Mt. at 0.6 % Cu, 0.35 g/t Au; Chinova Re-
sources, 2017), is located along the Mount Elliot Fault zone, at the
contact between the Soldiers Cap Group and the Staveley Formation.
The mineralization is essentially hosted within brecciated albitite and
calcareous sediments of the Staveley Formation, which is bounded by
altered banded calc-silicate rocks (Duncan et al., 2014). It is partly
hosted within quartz-mica schist of the Soldiers Cap Group and below a
thick metabasalt body. The calc-silicate alteration assemblage (scapo-
lite, actinolite, apatite, magnetite, epidote, garnet, calcite and chlorite)
is developed in carbonates, while siliciclastic sedimentary rocks contain
albite, hematite, biotite, and quartz, which vary in thickness between
0.5 and 10 cm (Wang and Williams, 2001). The breccia contains sub-
angular to rounded hematized albitite clasts in a matrix consisting of an
alteration assemblage (albite, hematite, actinolite, magnetite and chal-
copyrite) similar to those in the carbonate rocks. The occurrence of
pyrite-chalcopyrite mineralization is evidenced by intergrowths with
calc-silicate minerals (Wang and Williams, 2001). Magnetite deposition
is generally overprinting by this mineralization. The rocks have been
regionally metamorphosed from greenschist to amphibolite facies.

5. Geochemical footprints

We have compiled the major and trace element geochemical analyses
of whole rocks from the main IOA, IOCG, and porphyry deposits in
northern Norrbotten (Kiirunavaara, Rakkurijärvi, Nautanen, Aitik,
Sahavaara and Kolari) and their immediate igneous host rocks to char-
acterize regional geochemical footprints. These data were compiled
from the public databases of the Geological Surveys of Sweden and
Finland (e.g., Rasilainen et al., 2007), and correspond to surface rock
samples and drill cores. Only data located within 5 km of the deposits
were used. This dataset consists of 1236 individual whole-rock analyses
in total from the northern Norrbotten province, including 168 from the
Kiirunavaara area, 81 from the Rakkurijärvi area, 270 from the Nauta-
nen area, 195 from the Aitik area, 218 from the Sahavaara area, and 304
from the Kolari area. For the SWAN and Ernest-Henry deposits in the
Cloncurry district (Australia), we used lithogeochemical databases of
the Geological Survey of Queensland (Dhanaram et al., 2021).

After compiling the data, we characterized the geochemical foot-
prints of the areas around the deposits by calculating the molar pro-
portions of the major cations (Na, Ca, K, Fe, Mg). The molar barcodes are
plotted in the AIOCG diagram for MIAC systems (Montreuil et al., 2013)
to visualize the evolution of alteration facies and define metasomatic
pathways (Blein et al., 2022; Corriveau et al., 2022b; Drejing-Carroll
et al., 2023). Interpretation of the molar barcodes can be challenging
due to the large volume of data. To help differentiate alteration facies
and their evolution, a hierarchical cluster analysis (HCA) was carried out
using the molar proportions of Na, Ca, Fe, K and Mg. The HCA method
effectively highlights the least-altered facies, the main alteration types
and the alteration superimpositions.

5.1. Northern Norrbotten district

5.1.1. Kiruna district

Lithogeochemical samples collected within a 5 km radius of the
Kiirunavaara IOA deposit show several trends when plotted in the
AIOCG diagram (Fig. 5A): i) a trend from the least-altered field to the Na
alteration field; ii) a trend from the least-altered rocks to the Ca—Fe
alteration field; iii) a horizontal trend starting in the Na field and
continuing in the Na-Ca-Fe and Ca—Fe alteration fields; and iv) finally a
trend that starts in the Na field and continues through the K—Fe field.
The presence of albitite superimposed by Ca—Fe or K—Fe alteration is
<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Diagnostic trends showing the metasomatic evolution of the Kiirunavaara (A) and Rakkurijärvi (B) IOA deposits. These diagnostic trends are based on samples from the Geological Survey of Sweden (SGU) lithogeochemistry database. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. Blue trend: prograde metasomatism. See Fig. 1 for molar barcode legend and on all IOCG diagrams. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

indicated by a progressive decrease of Na molar proportion, as well as by the persistence of Na molar proportion in samples plotting in the Fe-rich Ca—Fe or K—Fe alteration fields. Fe-rich skarn (Ca-Fe-Mg dominated), skarn (Ca—Mg dominated), and apatite-rich magnetite ore (Ca—Fe dominated) follow a Ca—Fe to Fe-rich Ca—Fe trend (Corriveau et al., 2022b; Blein et al., 2023). In summary, the Kiirunavaara IOA deposit comprises hydrothermal alteration mineral assemblages that evolved from early Na and Na-Ca-Fe to later HT K—Fe facies, with a transition to the HT Ca—Fe facies.

Lithogeochemical samples collected within a 5 km radius of the Rakkurijärvi IOCG deposit are separated into Na—K and Na-Fe ± Mg-K dominated groups. Samples also exhibit trends from the Na alteration field towards the Ca-K-Fe and K—Fe alteration fields (Fig. 5B). These trends are characterized by a progressive increase of Fe and K molar proportions. This trend cuts across the field of least-altered rocks. Altered samples are distinguished from least-altered rocks by unbalanced barcodes dominated by three elements, mainly Fe, Na and Mg (or K). This evolution reflects an early albitization, gradually superimposed by K—Fe and Fe-rich K—Fe alteration. Samples from the Rakkurijärvi deposit also defined minor trends from the weakly altered field towards the Na and Ca—Fe alteration fields (Fig. 5B). In summary, the Rakkurijärvi deposit contains alteration assemblages that have evolved from early Na metasomatism to predominantly Fe-rich HT K—Fe facies. This metasomatic evolution is consistent with the paragenetic assemblages described by Smith et al. (2007).

### 5.1.2. Gällivare district

In the Nautanen IOCG deposit, metasomatic facies plot mainly in K—Fe and Ca-K-Fe alteration fields (Fig. 6A). Most samples exhibit barcodes dominated by Fe, K, and Ca. Na—K dominated group, in the weakly altered rocks field, have barcode signatures equivalent to felsic magmatic rocks, and Na-Fe ± Mg-K dominated group define trends. A HCA distinguishes five main groups.

Iron, K and Ca dominate the molar proportions of Group 1 (Fig. 6B). These rocks show a trend (yellow) with molar proportions ranging from those of weakly altered rocks to K—Fe dominated. Potassium, Fe and Ca dominate the molar proportions of Group 2 (Fig. 6C). These samples are associated with weakly altered mafic and intermediate rocks and define a vertical yellow trend from the weakly altered field towards the Ca-K-Fe and K—Fe alteration fields. Iron and K dominate the molar proportions of Group 3 (Fig. 6D). Samples of Group 3 define a vertical blue trend from the field of Fe-rich Ca—Fe alteration to Fe-rich K—Fe alteration field (Fig. 6D). This vertical blue trend suggests the existence of K—Fe

alteration superimposed on an earlier Ca—Fe alteration assemblage. Iron, Na and Ca dominate the molar proportions of Group 4 (Fig. 6E). Samples plot mainly in weakly altered rocks and Ca-K-Fe alteration fields. Rocks in the weakly altered field have slightly Na dominated molar proportions. These rocks also have a high molar proportion of Ca—Fe, or K—Fe, suggesting that they were affected by Na alteration before being overprinted by Ca—Fe or K—Fe alteration (white trends). Finally, Na and K dominate the molar proportions of Group 5 (Fig. 6F). Samples plot in weakly-altered felsic rocks and Na alteration fields (yellow trend; Fig. 6F). In summary, the Nautanen IOCG deposit is characterized by initial Na alteration, which is superimposed by successive Ca—Fe, Ca-K-Fe and K—Fe alteration facies.

In the Aitik porphyry Cu—Au deposit, the samples plot in weakly altered rocks and Ca-K-Fe, K—Fe, Fe-rich K—Fe, and K alteration facies (Fig. 7A). A HCA distinguishes four main groups.

The first group is composed of samples plotting in the weakly-altered rocks field (Fig. 7B). Na dominates the molar proportions with balanced Ca-Fe-K-Mg molar proportions. One sample is situated within the Na alteration field and exhibits a high Na enrichment indicative of albitites. Potassium and Fe dominate the molar proportions of Group 2 (Fig. 7B). Samples define a trend from weakly-altered rocks towards the K—Fe alteration field, culminating in the K alteration field (Fig. 7B). Calcium, Fe and K dominate the molar proportions of Group 3 (Fig. 7C). Samples are distinguished by a progression from the field of weakly-altered mafic and intermediate rocks towards the Ca-K-Fe and K—Fe alteration fields, respectively, as evidenced by the increasing molar proportions of K and Fe (Fig. 7C). Iron and K dominate the molar proportions of Group 4 (Fig. 7D). Samples plot in the Ca-K-Fe and K—Fe alteration fields. In weakly-altered rocks and Ca-K-Fe alteration fields, a non-negligible Na molar proportion persists in samples plotting in the Ca-K-Fe alteration field. The persistence of a non-negligible molar proportion of Na is symptomatic of a K—Fe alteration overprinted on earlier albitized rocks.

A comparison of the metasomatic evolution for the Aitik and Nautanen deposits is presented in Fig. 8. In the Aitik deposit, Si and Al do not dominate the molar proportions, as might be expected for a porphyry system (Corriveau et al., 2018, 2022a). In the Aitik deposit, Si and Al have slightly higher molar proportions (avg = 0.25) than in the Nautanen deposit (avg = 0.23). The higher Si and Al molar proportions in the Aitik deposit explains the shift of the samples to the left of the diagram, compared with samples from the Nautanen deposit. However, the great similarity in the evolution of molar proportions between the two deposits clearly indicate the existence of a MIAC-type metasomatic process for the Aitik deposit. The widespread sericitization of the Aitik
<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Diagnostic trends showing the metasomatic evolution of the Nautanen IOCG deposit based on samples from the Geological Survey of Sweden (SGU) litho-geochemistry database. A: full dataset; B: Group 1; C: Group 2; D: Group 3; E: Group 4; and F: Group 5. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. Blue trend: prograde metasomatism. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

deposit share similarities with Facies 6 sericitic alteration of MIAC systems (Mumin et al., 2010; Corriveau et al., 2022a). A similar mineral assemblage of muscovite + pyrite and chlorite + sericite + magnetite ± epidote from altered LT K-Fe facies rocks has also been reported from the Nautanen North deposit (Drejing-Carroll et al., 2023).

In conclusion, the Aitik porphyry Cu-Au deposit is distinguished by early Na alteration influenced by superimposed K-Fe and Ca-K-Fe alteration facies, like in the Nautanen and Nautanen North deposits.

The typical alteration associated with porphyry-type mineralization cannot be identified from this database and requires further investigation to test and validate the porphyry origin of the Aitik Cu-Au-Ag-Mo mineralization.

### 5.1.3. Pajala-Kolari district

Samples from the Sahavaara IOCG deposit and its various mineralized zones plot essentially in the field of weakly-altered rocks (Fig. 9A).
<figure><img src="image_10.png" /><figcaption>Fig. 7. Diagnostic trends showing the metasomatic evolution of the Aitik porphyry Cu—Au deposit based on samples from the Geological Survey of Sweden (SGU) lithogeochemistry database. A: full dataset; B: Groups 1 and 4; C: Group 2; D: Group 3. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>Fig. 8. Diagnostic trends showing the metasomatic evolution of the Aitik porphyry Cu—Au deposit (A) and Nautanen IOCG deposit (B) based on samples from the Geological Survey of Sweden (SGU) lithogeochemistry database using Na-Ca-Fe-K-(Si + Al)/10 barcodes.</figcaption></figure>

However, it is possible to distinguish between Na, Ca—Fe, and Fe-rich Ca—Fe alteration types. Group 1 is comprised of rocks that fall within the least-altered rock field and that are either only weakly altered or show overprinting relationships on albitite (Fig. 9B). They have generally high molar proportions of Na associated with: i) four elements (Mg, Fe, K, Ca) having the same or similar proportions, which is typical of

increasingly albitized rocks with trends starting from felsic to mafic host rocks (yellow trend, Fig. 9B); ii) high proportions of Ca, Mg, and Fe and minor proportions of K typical of albitized mafic rocks with increasing overprints of Ca-K-Fe alteration (white trend, Fig. 9B); and iii) high proportions of K and Fe typical of albitite overprinted by K—Fe alteration (white trend, Fig. 9B). Some rocks with high molar proportions of
<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Diagnostic trends showing the metasomatic evolution of the Sahavaara IOCG deposits based on samples from the Geological Survey of Sweden (SGU) litho geochemistry database. A: full dataset; B: Group 1; C: Group 2; D: Groups 3, 4, and 5. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

K and Fe lie between the K and K-Fe alteration fields (Fig. 9B). Calcium, Mg and Fe dominate the molar proportions of Group 2 (Fig. 9C). Samples fall within the field of weakly-altered mafic rocks and Ca-Fe alteration fields (Fig. 9C). Mafic rocks have barcodes whose molar proportions are dominated by Ca, Mg, Fe, and Na, representing the primary mineral-ogical composition of basalt and gabbro. The Ca-Fe alteration results in a progressive increase in the molar proportions of Ca and Fe. Potassium and Na dominate the molar proportions of Group 3 (Fig. 9D). Samples plot in the least-altered felsic rocks field and are characterized by i) an increase in K ± Fe or ii) an increase in Na that reaches very high molar proportions of Na while maintaining balanced Ca-K-Fe-Mg proportions diagnostic of albitite, plus a few transitional facies (Fig. 9D). The latter are more or less albitized with higher or lower molar proportions of Na. The fourth group is composed of skarns, which are characterized by molar proportions dominated by Ca and Mg (Fig. 9D). Iron dominates the molar proportions in Group 5 (Fig. 9D). Some rocks exhibit a non-negligible molar proportion of Na in their barcodes, indicating the superimposition of Fe-rich Ca-Fe alteration on former albitite.

Samples from the Kolari IOCG deposits exhibit comparable barcodes and trends to those from Sahavaara (Fig. 10). They are mainly situated within the field of weakly-altered rocks, although albitite and Fe-rich Ca-Fe, Ca-Fe, and K alteration types can be discerned (Fig. 10A). Potassium dominates the molar proportions in Group 1. Samples plot within the fields of K alteration (Fig. 10B). Iron, Mg and K dominate the molar proportions in Group 2. Samples plot mainly within weakly altered rocks (Fig. 10B). However, most barcodes exhibit characteristics that are atypical of least-altered rocks, including very low Ca molar

proportion, high Mg and Fe molar proportions and non-negligible Na molar proportion. Such a change in molar proportions indicates K-Fe alteration superimposed on Na alteration. Magnesium, Ca and Fe dominate the molar proportions in Group 3. This group consists of weakly-altered mafic rocks and Ca-Fe altered rocks (Fig. 10C). Mafic rocks exhibit barcodes with molar proportions dominated by Ca, Fe, and Mg, with systematically minor Na and K molar proportions. Ca-Fe alteration results in a progressive increase in the molar proportions of Ca and Fe. Sodium, K and Fe dominate the molar proportions in Group 4. Samples fall within the field of weakly-altered rocks and the Na and K-Fe alteration fields (Fig. 10D), suggesting a later K-Fe alteration superimposed on albitite having >75 % of Na molar proportion. At the boundary between the fields of Na alteration and weakly-altered rocks, samples have Na dominated molar proportions, the other components being balanced, which is typical of albitized felsic to intermediate rocks (yellow trend, Fig. 10D). A small number of samples have molar proportions dominated by Na, in association with Ca-Fe, Ca-K-Fe, or K-Fe alteration (white trend, Fig. 10D). These samples correspond to albitite with superimposed Ca-Fe, Ca-K-Fe, or K-Fe alteration. Iron highly dominates molar proportions in Group 5. Samples are highly enriched in Fe, with barcodes composed almost exclusively of Fe, locally with a low molar proportion of Na. This reflects the residues of a former albitite.

## 5.2. Cloncurry district

### 5.2.1. Ernest-Henry deposit

Samples from the Ernest-Henry deposit are found to be essentially in
<figure><img src="image_13.png" /><figcaption>**Fig. 10.** Diagnostic trends showing the metasomatic evolution of the Kolari IOCG deposits based on samples from the Geological Survey of Finland (GTK) litho geochemistry database (Rasilainen et al., 2007). A: full dataset; B: Group 1; C: Group 2; D: Groups 3 and 4. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

the weakly-altered, Ca—Fe, Ca-K-Fe, K—Fe, and Fe-rich fields (Fig. 11A). Barcodes are systematically characterized by a high molar proportion of Fe associated with: i) a high molar proportion of K; ii) a high molar proportion of Ca; or iii) a high molar proportion of Na. A HCA distinguishes five main groups.

Calcium and Fe dominate molar proportions in Group 1, in associa-
tion with Na or K. Samples plot in weakly-altered rocks, Ca—Fe and Ca-
K-Fe alteration fields (Fig. 11B). Group 1 comprises weakly altered in-
termediate to slightly more mafic rocks, with molar proportions domi-
nated by Ca, Na, Fe, and Mg. These barcodes progress to Ca-K-Fe and
K—Fe alteration (yellow trends, Fig. 11B). The Ca-K-Fe alteration foot-
print results from a progressive decrease in Na and Mg molar pro-
portions, concomitant with an increase in Fe and K molar proportions,
while the Ca proportion remains relatively stable. These barcodes may
correspond to only moderately altered intermediate rocks along the
trend towards K—Fe alteration (Fig. 11B). Iron dominates molar pro-
portions in Group 2, in association with Na or K. This second group is
characterized by two distinctive trends. The first trend corresponds to a
gradual decrease in Na, a slight increase in Ca, and by a sharp rise in Fe
molar proportion (Fig. 11C). In the Ca—Fe field, the barcodes still show
a significant molar proportion of Na. This trend is characteristic of Fe-
rich Ca—Fe alteration superimposed on albitite. The second trend con-
sists of an evolution from the Fe-rich Ca—Fe to the K—Fe alteration field
(Fig. 11C). This evolution is reflected by a gradual increase in the molar
proportion of K, with a non-negligible molar proportion of Na. Iron

dominate molar proportions in Group 3. Samples plot in the Fe-rich
alteration fields (Fig. 11D). These samples define a prograde path
from the Fe-rich Ca—Fe alteration field to the Fe-rich K—Fe alteration
field (vertical blue trend, Fig. 11D). Iron and K dominate molar pro-
portions in Group 4. Samples plot in the K—Fe alteration field. These
samples define a trend from barcodes dominated by Ca, K, and Fe, to
barcodes dominated by K and Fe (oblique blue trend, Fig. 11D). In
summary, the Ernest-Henry IOCG deposit is characterized by an early Na
alteration, which is later superimposed by Ca—Fe, Ca-K-Fe, and K—Fe
alteration assemblages.

5.2.2. SWAN deposit

Samples from the SWAN deposit essentially plot in the weakly-
altered rocks field, including that of skarn as well as in the Ca-Na-Fe,
Ca-Fe, and Fe-rich Ca-Fe alteration fields (Fig. 12A). Most of the
data form a trend extending from the field of mafic volcanic rocks and
skarn to the field of Fe-rich Ca-Fe alteration. The HCA distinguishes
four main groups.

Iron or Ca and Fe dominate molar proportions in Group 1. Samples define a trend between least-altered mafic volcanic rocks and skarn, with increasing Na proportions across the Na-Ca-Fe field (yellow trend, Fig. 12B). Another trend is observed towards the field of Fe-rich Ca-Fe alteration (yellow trend, Fig. 12B). This latter trend is reflected by increasing molar proportions of Fe, decreasing molar proportions of Ca, and remaining molar proportions of Na. Some samples in the Na-Ca-Fe
<figure><img src="image_14.png" /><figcaption>**Fig. 11.** Diagnostic trends showing the metasomatic evolution of the Ernest-Henry deposit based on samples from the Geological Survey of Queensland litho geochemistry database (Dhanaram et al., 2021). A: full dataset; B: Group 1; C: Group 2; D: Groups 3 and 4. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. Blue trend: prograde metasomatism. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

field exhibit barcodes dominated by Na, Ca, and Mg (Fig. 12B). Given that the deposit hosts extensive skarn assemblages that have been albitized, this trend cannot be simply interpreted as indicating early Na—Ca alteration prior to Ca—Fe alteration, as is typical of many MIAC systems. However, the extensive Mg proportion instead of Fe with Ca is indicative of either albitization of a skarn, as described for the SWAN deposit, or LT Ca—Mg alteration of albitite, as observed in the Michelin deposit studied by Acosta-Góngora et al. (2022). Nevertheless, early Na—Ca alteration is necessary to explain the persistent Na proportions in the Ca—Fe and Fe-rich Ca—Fe alteration fields. A small number of samples that are rich in Fe also show a slight increase in the proportion of K and fall within the Fe-rich K—Fe alteration field (blue trend, Fig. 12B). This could indicate late K or K—Fe alteration that occurred after the significant Fe-rich Ca—Fe alteration. A small number of barcodes, which are composed essentially of Ca and Fe, may represent extensive Ca—Fe alteration of the previously more Mg-rich skarn or Ca—Fe alteration of mafic host rocks.

Calcium highly dominates molar proportions in Group 2 (Fig. 12C), these samples correspond to carbonate rocks. The high molar proportion of Ca is associated with a non-negligible proportion of Na, Fe, or K, which are related to albitization, Fe enrichment, and K alteration, respectively. Potassium and Fe, or Na dominate molar proportions in Group 3. Samples primarily plot within the field of weakly-altered rocks. Two distinct trends can be observed within this group: i) a trend towards the Na alteration field and albitite (Fig. 12C); and ii) a second trend towards the K—Fe alteration field (Fig. 12C). One sample is

characterized by a barcode dominated by Na, associated with Ca and Fe (Fig. 12C), reflecting the presence of an albitite on which Ca—Fe alteration is superimposed (white trend, Fig. 12C). Iron, K and Na dominate molar proportions in Group 4. Samples plot mainly in the field of weakly-altered rocks. These samples have barcodes dominated by three elements, Na, Fe, and K, in order of importance with Mg proportions remaining relatively constant. All samples exhibit a trend from the Na to the K—Fe alteration field (Fig. 12D). These samples reflect K—Fe alteration superimposed on previously albitized samples. In summary, the SWAN IOCG deposit is characterized by an early Na alteration of all host rocks, including skarn, with albitized rocks and skarn overprinted by later Ca—Fe and K—Fe alteration types.

# 6. Discussion

## 6.1. Evolution of metasomatic footprints in the Norrbotten and Cloncurry MIAC systems

The metasomatic evolution of the Kiirunavaara, Rakkurijärvi, Nau-tanen, and Pajala-Kolari deposits is summarized on the AIOCG diagram of Montreuil et al. (2013) with characteristic barcodes for each trend (Fig. 13A-D). This figure shows the main metasomatic paths of these deposits, and the evolution of barcodes along these metasomatic paths.

In the Kiirunavaara area (Fig. 13A), analysis of lithochemical data combined with barcode representation reveals that the main metasomatic trends originate from the weakly-altered field and proceed
<figure><img src="image_15.png" /><figcaption>**Fig. 12.** Diagnostic trends showing the metasomatic evolution of the SWAN deposit based on samples from the Geological Survey of Queensland lithogeochemistry database (Dhanaram et al., 2021). A: full dataset; B: Group 1; C: Groups 2 and 3; D: Group 4. Yellow trend: alteration from weakly altered to most altered rocks. White trend: overprints on albitite. Blue trend: prograde metasomatism. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

towards Na or Ca—Fe alteration. They are also distinguished by K—Fe overprints on the albitites. In northern Norrbotten, IOA deposits, such as the Kiirunavaara deposit, are mainly associated with Na—Ca (Frietsch et al., 1997; Bergman et al., 2001) and Ca—Fe alteration facies (Nordstrand and Andersson, 2013). The Kiirunavaara IOA deposit is composed of a magnetite-apatite orebody with magnetite-actinolite breccias (Bergman et al., 2001). Actinolite is a common alteration mineral at both the footwall and the hanging wall contacts, and the hanging wall is in some areas affected by biotite-chlorite alteration (Bergman et al., 2001). Common alteration minerals in the host rocks surrounding the deposit include albite, scapolite, actinolite, and biotite in variable amounts (Bergman et al., 2001). Albitization of the host rocks is also common and extensive (Bergman et al., 2001; Barton, 2014). Geochemical data suggest the existence of K—Fe alteration superimposed on albitized rocks.

The Rakkurijärvi IOCG deposit is characterized by a K—Fe alteration, more or less enriched in iron, superimposed on early albitization (Fig. 13B). Additionally, the deposit exhibits a metasomatic path ranging from weakly-altered rocks to Ca—Fe alteration, and from weakly-altered rocks to Na alteration. The Rakkurijärvi deposit exhibits a similar degree of albitization to the Kiirunavaara IOA deposit, with the alteration later overprinted by K—Fe alteration with varying Fe enrichment, and similar Ca—Fe alteration. In the Rakkurijärvi deposit, the alteration sequence is characterized by pervasive sodic alteration, magnetite-actinolite alteration overlying albitic alteration, and biotite and potassium feldspar overlying albitic alteration and magnetite-

actinolite-albite assemblages (Smith et al., 2007). This alteration para-
genesis is consistent with observations based on geochemical data. Due
to the widespread albitization, the Rakkurijärvi deposit is distinguished
by alteration trends that diverge from the general trends observed across
the MIAC systems of the GBMZ and at Olympic Dam (Fig. 2). However,
the observed trends and barcodes are highly analogous to those
observed in other U or Cu—Au mineralization hosted by albitites (e.g.,
Cole U prospect in the GBMZ; Montreuil et al., 2016b; Two-time pros-
pect and Michelin deposit of the Central Mineral Belt of Labrador;
Acosta-Góngora et al., 2022).

In the Gällivare district, the Nautanen IOCG deposit area is charac-
terized by Ca-K-Fe and K-Fe alteration facies superimposed on albitized
rocks, as well as by a prograde path starting from strongly altered Fe-rich
Ca-Fe field facies and ending with strongly altered K-Fe facies
(Fig. 13C). Like for the Kiirunavaara and Rakkurijärvi deposits, analysis
of a large lithogeochemical dataset combined with barcode represen-
tation confirms widespread albitization, with Ca-Fe and/or K-Fe
alteration facies superimposed on the former (Fig. 13C). The Nautanen
deposit is also characterized by a trend of increasing alteration intensity
from weakly-altered rocks to the K-Fe alteration field (Fig. 13C). The
Nautanen deposit differs from the Rakkurijärvi deposit in that K-Fe
alteration is more widespread and Ca-Fe alteration has evolved to-
wards K-Fe alteration. However, these alteration trends are consistent
with the alteration paragenesis described for the Nautanen North
Cu-Au deposit (Drejing-Carroll et al., 2023).

In the Nautanen North deposit, Na alteration is extensively replaced
<figure><img src="image_16.png" /><figcaption>Fig. 13. Summary of the main metasomatic trends in IOCG-IOA-style deposits of northern Norrbotten and Cloncurry districts, illustrated by the evolution of molar barcodes along these paths. A: Kiirunavaara; B: Rakkurijärvi; C: Nautanen; D: Pajala-Kolari; E: Hernest-Henry; F: SWAN.</figcaption></figure>

by Na-Ca-Fe, HT Ca—Fe (amphibole, magnetite, ± garnet, ± epidote replacement and veining), transitional HT Ca-K-Fe (amphibole + biotite + K-feldspar + magnetite ± garnet), HT K—Fe (biotite + magnetite + K-feldspar ± sericite), and LT K—Fe (sericite-dominated assemblage with K-feldspar + garnet ± biotite) alteration facies (Drejing-Carroll et al., 2023). As the rocks were metamorphosed to the HT Ca-K-Fe facies and the HT Ca—Fe overprinted by HT K—Fe are now an amphibole-biotite gneiss, the HT K—Fe facies is a biotite gneiss, and the LT K—Fe alteration is a muscovite-garnet gneiss (Drejing-Carroll et al., 2023).

The geochemical footprint of the Aitik deposit includes widespread albitization, with Ca-K-Fe and K—Fe alteration superimposed on the

formerly albitized rocks (Fig. 6). Worldwide, prograde metasomatic pathways associated with significant and extensive Fe enrichment are not observed in porphyry systems (Sillitoe, 2010; Richards and Mumin, 2013). Rather, altered facies for Aitik are slightly shifted to the left side of the AIOCG diagram and exhibit large proportions of Mg, Si, Al, and K in their barcodes due to chloritization, silicification, and potassic alteration, respectively (Fig. 7). Given the contrasting alteration styles between porphyry and IOCG deposits (Corriveau et al., 2022b), barcodes should reflect the difference between these two ore-forming systems. The alteration trends at the Aitik deposit are also similar to the alteration trends at the Nautanen deposit. The paragenesis of alteration
at Aitik has been established by careful observation of cross-cutting and overprinting (replacement) relationships (Wanhainen et al., 2012). The main changes in the mineralogy of the rocks include the replacement of plagioclase by K-feldspar, sericite, scapolite, epidote and calcite; of biotite by amphibole, K-feldspar, chlorite, epidote, tourmaline, and muscovite; and of amphibole by biotite, K-feldspar, tourmaline and apatite (Wanhainen et al., 2012). The main copper-bearing mineral is chalcopyrite, and other opaque minerals include pyrite, magnetite, pyrrhotite, ilmenite, and molybdenite. The barcodes established for the Aitik deposit clearly indicate the presence of hydrothermal K-Fe alteration. Mineralogical descriptions do not highlight this Fe enrichment, which is present in sulfide and silicate minerals. Magnetite replacement by sulfide has been documented at the Nautanen North deposit, however.

In the Pajala-Kolari district, analysis of available lithogeochemical datasets, combined with the barcode representation, shows that Cu-Au deposits officially classified as IOCG-type deposits have metasomatic footprints that are distinct from typical magnetite-rich and hematite-rich IOCG deposits (Fig. 2). The geochemical footprint in the Pajala-Kolari district is typical of HT Ca-Fe and K-Fe alteration facies that overprint and increasingly replace regionally albitized host rocks (Fig. 13D), as illustrated by the IOA and IOCG deposits in the Kiruna district. The Pajala-Kolari district hosts numerous deposits that vary considerably in host rocks, mineralization styles, and in size, Fe, Cu and Au grades. Mineralizations range from massive to semi-massive magnetite lenses, breccias and disseminated magnetite-Cu-Au bodies (Niiranen et al., 2007). Several Fe deposits have been classified as IOCG deposits (e.g., Hannukainen and Rakkurjärvi; Niiranen et al., 2007). However, proximal alteration facies differentiate IOCG deposits from Fe-rich skarn deposits containing Cu and Au. In the Kolari and Pajala region, the distal alteration zone is characterized by albite ± biotite, K-feldspar, and scapolite, and the proximal zone by clinopyroxene-magnetite ± amphibole, scapolite, calcite, and sulfides (Niiranen et al., 2007; Billström et al., 2010). In the Laurinoja and Kuervitikko deposits, the skarns consist mainly of clinopyroxene (diopside-hedenbergite) and amphibole (actinolite-hornblende) dominated rocks (Niiranen et al., 2007). In addition, rocks consisting mainly of albite with varying amounts of biotite, amphibole, K-feldspar and quartz are common. In the Cu-Rautuvaara deposit, the Cu-Au ore is hosted by magnetite-disseminated, biotite-anthophyllite-bearing albite (Niiranen et al., 2007). The metasomatic evolution observed in the MIAC deposits of northern Norrbotten is strongly influenced by the development of early albitization on a regional-scale, which precedes systematic overprinting by Ca-Fe and K-Fe alteration facies associated with Cu-Au mineralization.

The metasomatic evolution of the Ernest-Henry and SWAN deposits of the Cloncurry district is summarized on the AIOCG diagram of Montreuil et al. (2013) with characteristic barcodes for each trend (Fig. 13E-F). The Ernest-Henry deposit is characterized by HT Ca-Fe superimposed on albitized rocks, by HT K-Fe alteration facies superimposed on HT Ca-Fe alteration facies, as well as by a prograde path starting from strongly altered Fe-rich Ca-Fe field facies and ending with strongly-altered K-Fe facies (Fig. 13E). The alteration paragenesis is characterized by actinolite-magnetite and K-feldspar-magnetite assemblages, with K-feldspar clearly posterior to albite (Emproto et al., 2022; Schlegel et al., 2022). Moreover, albite dominates the medial and distal alteration footprints. The median alteration footprint is characterized by the replacement of albite and actinolite by magnetite and biotite (Schlegel et al., 2022). Geochemical data confirms the existence of early albitization superimposed by Ca-Fe alteration, followed by K-Fe alteration.

In the SWAN deposit (Fig. 13F), analysis of lithogeochemical data combined with barcode representation reveals that many metasomatic trends originate from the weakly-altered field and proceed towards Na, Ca-Fe and K-Fe alteration. They are also distinguished by K-Fe overprints on the albitites, and by a prograde path starting from Fe-rich

Ca-Fe facies and ending within Fe-rich K-Fe facies. In the SWAN deposit, mineralization is hosted in a large breccia surrounded by a variably mineralized but distinctive banded calc-silicate-altered rocks (Brown, 2010). A calc-silicate assemblage (diopside, actinolite, calcite, chlorite, magnetite, scapolite, epidote, tremolite, titanite, anhydrite, and gypsum) is preferentially developed in the carbonate-rich psammitic layers, and the pelitic layers contain hematite-stained albite, quartz, and biotite (Wang and Williams, 2001; Brown et al., 2009). The SWAN breccia typically contains hematite-stained albite clasts (Duncan et al., 2014). Within this deposit, iron enrichment is linked to the presence of iron-rich sulfides and silicates, rather than to the presence of iron oxides. Geochemical data also confirms the existence of early albitization superimposed on Ca-Fe alteration, followed by K-Fe alteration.

Early albitization is one of the outstanding features of the metasomatic evolution of the Norrbotten and Cloncurry districts. This is illustrated, for example, by similar metasomatic trends observed in the Nautanen and Ernest-Henry deposits on the one hand, and in the Pajala-Kolari and SWAN deposits on the other. These regional albitite corridors are facilitated by regional shear zone zones, fracturing within damage zones, and brecciation of the host rocks. Because of their intrinsic porosity, these albitite zones are preferential sites for subsequent metasomatism and/or mineralization (Montreuil et al., 2015; Fox et al., 2023).

## 6.2. Relation between Cu mineralization and metasomatic footprints

In the Rakkurjärvi IOCG deposit, most Cu-rich samples fall into the weakly-altered field (Fig. 14A). The barcodes, which show high proportions of Na and Fe, indicate that these mineralized facies have undergone albitization followed by a Fe-rich K-Fe alteration overprints (Fig. 14B). The paragenetic evolution of the Rakkurjärvi deposit is characterized by early Na-rich alteration followed by massive magnetite alteration of the HT Ca-Fe facies (Smith et al., 2007). A K-Fe alteration with magnetite is also superimposed on the Na-rich alteration. The sequence of alteration and mineralization is complex and several episodes of sodic and potassic alterations have been identified (Smith et al., 2007).

In the Nautanen IOCG deposit, most of the Cu-rich samples are located mainly in the fields of K-Fe, Ca-K-Fe and Fe-rich alterations (Fig. 14C). The main Cu-rich group is associated with K-Fe alteration, similar to the classic IOCG of the magnetite-group (Fig. 14D). Some barcodes show a significant proportion of Na, which may record an early albitization before deposition of the Cu-Au mineralization.

In the Aitik Cu-Au deposit (Fig. 14E), the samples rich in Cu are mainly found in the field of weakly-altered, K ± Fe, K-Fe, Ca-K-Fe and Fe-rich alteration zones. The clusters with high Cu contents in K-Fe and Ca-K-Fe fields are like those of the Nautanen deposit and those of the classic magnetite-group IOCG (Fig. 14F). The other clusters within the weakly-altered rocks and K ± Fe fields are not characteristic of IOCG deposits as might be expected given the demonstrated existence of two superimposed mineralizing events, including one which is more similar to that of porphyry deposits.

In the Pajala-Kolari district, the Cu-rich samples are found in the fields of Na-Ca-Fe, Ca-Fe and Fe-rich Ca-Fe alteration facies, and weakly-altered rocks (Fig. 14G). The barcodes are characterized by varying proportions of Na, Ca, Fe and K (Fig. 14H). In the field of weakly-altered rocks, the barcodes are dominated by the Na-K or Na-Ca-K-Fe alteration facies. Those correspond to albitite overprinted by K-Fe or Ca-K-Fe alteration. In the Na-Ca-Fe field, the barcodes are dominated by Na-Fe or Na-Ca-Fe. These are albitites overprinted by Ca-Fe alteration of varying Fe contents. At the boundary between the Ca-Fe and Fe-rich Ca-Fe fields, the barcodes, dominated by Ca and Fe in proportions variables, are characteristic of Fe-rich skarn. Finally, in the Fe-rich Ca-Fe field, the barcodes, composed almost exclusively of Fe, are characteristic of Fe oxide-rich lenses. The barcodes show that the
<figure><img src="image_17.png" /><figcaption>**Fig. 14.** Distribution of Cu contents and corresponding barcodes (samples >2000 ppm Cu) for the Rakkurjärvi (A-B), Nautanen (C—D), Aitik (E-F), and Pajala-Kolari (G-H) deposits.</figcaption></figure>
Cu mineralized facies are hosted in albitite, skarn, or magnetite-rich lenses.

In the ODBC, high Cu concentrations (16,000 to 121,000 ppm Cu; Fig. 17 in Corriveau et al., 2022b) are found in samples located in the Fe-rich Ca-K-Fe alteration field and extend from the K—Fe field towards the Fe-rich fields as hematization progresses. However, the main cluster is found in the Fe-rich Ca-K-Fe and Fe-rich Ca—Fe fields (Corriveau et al., 2022b) as carbonates and fluorite are present in some mineralized samples (Apukhtina et al., 2020). In the GBMZ, the highest Cu concentrations are found in samples located in the K—Fe field which is in line with the Cu being associated with K-feldspar rich HT K—Fe instead of lower temperature alteration facies with carbonates or fluorite (1000 to 50,000 ppm Cu in Fig. 15 of Corriveau et al., 2022b). In addition, few high Cu concentrations occur in albitized samples from the Na, Na-Ca-Fe, and weakly-altered fields that were overprinted by K—Fe alteration (Corriveau et al., 2022b).

In IOCG-type deposits, proximal alteration of Cu—Au mineralization is generally dominated by K- and Fe-rich mineral phases, which formed at high temperatures (magnetite-group IOCG) and low temperatures (hematite-group IOCG). In the northern Norrbotten district, proximal alteration of Fe-rich Cu—Au mineralization is more complex. Having a K—Fe alteration associated with mineralization is common, as seen in the Nautanen deposit. However, skarn-related mineralization can also be found, with proximal Ca—Fe alteration. The Kuervitikko and Laurinoja deposits are composed of silicate-banded to massive magnetite-rich lenses (ironstone), which are hosted in a skarn formed near the contact zone between the Savukoski Group and ca. 1.86 Ga-old dioritic and monzonitic intrusions (Hiltunen, 1982; Niiranen et al., 2007). Mineralized albitite zones with K—Fe alteration are also common due to

early and pervasive regional albitization. The Rautuvaara Cu deposit contains a significant amount of Cu—Au ore, which is mainly hosted in magnetite-disseminated, biotite- and/or anthophyllite-bearing albitite. This albitite forms an elongate lens that is approximately 45 m thick (Niiranen et al., 2007).

The Cloncurry district also exhibits a variety of mineralized alteration facies. The Ernest-Henry IOCG deposit is hosted in a breccia body rich in magnetite and K-feldspar-altered clasts which defines a HT K—Fe alteration facies (Mark et al., 2006; Corriveau et al., 2022a). In the deposit (Fig. 15A), rocks containing >1000 ppm of Cu are found mainly in the field of Fe-rich K—Fe, Fe-rich Ca-K-Fe, and Fe-rich Ca—Fe alteration zones. Part of the ore zone consists of a calcite-magnetite assemblage (Rusk et al., 2010; Corriveau et al., 2022a), an assemblage that falls within the Ca—Fe alteration facies and explains the range from the more common Cu-rich samples in the Fe-rich K—Fe field to the Ca—Fe field.

In the SWAN deposit, the Cu-rich samples fall within the fields of weakly altered, Ca—Fe, and Fe-rich Ca—Fe rocks (Fig. 15C). The barcodes are characterized by variable proportions in Na, Ca, and Fe (Fig. 15D). In the field of weakly-altered rocks, the barcodes are dominated by Na-Ca-Fe and correspond to calc-silicate altered rocks with early albitization superimposed on Ca—Fe alteration. In the Ca—Fe field, the barcodes are dominated by Ca and Fe in varying proportions. These skarns are more or less rich in Fe. Finally, in the Fe-rich Ca—Fe field, the barcodes are almost exclusively composed of Fe. These are lenses made up almost entirely of Fe oxides. At the SWAN deposit, protoliths of diopside-rich, skarn-hosted, Cu—Au ore are carbonaceous metapelites. Mineralization at SWAN is largely contained within a large breccia body surrounded by a variably mineralized but distinctly banded calc-silicate altered rocks (Brown et al., 2009). The banded texture is the

<figure><img src="image_18.png" /><figcaption>Fig. 15. Distribution of Cu contents and corresponding barcodes (samples >2000 ppm Cu) for the Ernest-Henry (A-B) and SWAN (C—D) deposits.</figcaption></figure>
result of the interbedded nature of the protolith at SWAN. A calc-silicate assemblage (actinolite, tremolite, diopside, calcite, scapolite, magnetite, chlorite, epidote, titanite, gypsum, and anhydrite) develops preferentially in the carbonate-rich psammitic layers and is typical of a HT Ca-Fe alteration facies overprinting a skarn or a calc-silicate rock. In contrast, the siliciclastic layers contain hematite-stained albite, quartz, and biotite. The SWAN breccia typically contains clasts of hematite-stained albite that are subangular to rounded in shape.

In Northern Norrbotten, Cu-Au mineralization is not exclusively represented by IOCGs systematically associated with brecciation and proximal K-feldspar rich K-Fe alteration (although locally developed). These Cu-Au mineralization zones are also associated with albitites, ironstones and Fe-rich skarns. Ironstones and Fe-rich skarns are characterized by proximal Ca-Fe alteration, and albitites by proximal K-Fe alteration. The same variability is observed in the Cloncurry district.

## 6.3. Na-Ca-Fe-K-Mg molar barcodes: A tool for predictive exploration

Metasomatism leading to the formation of IOAs, IOCGs and associated critical metal deposits in MIAC systems is intense and spatially extensive. The geochemical data presented here in discriminant AIOCG diagrams shows that the various metasomatic mineral assemblages correspond to distinct and diagnostic alteration facies, and to different deposit types. Each alteration facies comprises a distinctive set of mineral assemblages that correspond to distinct ranges in bulk rock chemical composition (Corriveau et al., 2022b; Fabris, 2022; Drejing-Carroll et al., 2023).

Important insights into the evolution of metasomatism in MIAC mineral systems and affiliated deposits are provided by whole-rock major element geochemistry. The molar barcodes define metasomatic pathways, help identify metasomatic processes, and delineate alteration trends (Blein et al., 2022; Corriveau et al., 2022b). Individually, they do not show the complete sequence of alteration facies and only record a part of a multiphase metasomatic system. However, at the regional scale, analysis of the barcodes, employing large lithogeochemical datasets, provides a complete sequence of alteration facies (if exposed or drilled into), and helps to optimize exploration targeting. At the deposit-scale, the molar barcode approach can also be used to indicate areas where alteration and mineralization were the most intense and can help to define geochemical proxies for vectoring ore zones from proximal to distal based on analyzed drill cores or surface samples. Furthermore, by combining trace element concentrations and barcodes with the AIOCG discriminant diagram of Montreuil et al. (2013), the enrichment of elements of economic interest, such as Cu and Au, can be traced during the progressive development of each alteration facies (Corriveau et al., 2022c).

In the northern Norrbotten district, analysis of the alteration facies in the vicinity of Fe-rich Cu-Au mineralization reveals a complex pattern. The occurrence of Fe-rich Cu-Au mineralization is not confined to IOCG-type deposits exhibiting proximal K-feldspar rich K-Fe alteration facies, a signature that develops particularly well in volcano-plutonic environments of intermediate to felsic composition. In contrast, the Norrbotten district is rich in mafic rocks which are known to provide ample Mg to the metasomatite, in addition to Fe. This district is additionally distinguished by the presence of Fe-rich Cu-Au mineralized skarns exhibiting proximal Ca-Fe alteration, as well as by albitite-hosted Fe-rich Cu-Au mineralization, which displays Na alteration overprinted by K-Fe alteration. As such, this study further illustrates the different types of Fe-rich Cu-Au mineralization precipitated within MIAC systems beyond IOCGs (Corriveau et al., 2022c; Hamilton et al., 2023). The use of Na-Ca-Fe-K-Mg molar barcodes facilitates the differentiation between the various mineralization or deposit types based on the distinctive proximal alteration facies associated with each. In summary, the molar barcodes appear as a powerful tool for guiding exploration from the district- to the deposit-scale and for targeting concealed orebodies using the geochemical signatures of the associated altered

host rocks. By choosing case studies where alteration parageneses of mineralization were available, we were able to demonstrate that interpreting large datasets can not only help best interpret the metasomatic evolution of known MIAC systems and their deposits but can be used to identify systems and assess their mineral potential.

## 7. Conclusions

Key conclusions derived from this work follow:

1. Metasomatic evolution of MIAC systems can be interpreted to a great extent by reporting large lithogeochemical datasets on the AIOCG diagram with barcodes. The application demonstrated that depending on the host geological environment, the evolution of the system, and the intensity of alteration overprints on albitite, a wide array of deposit types can form and differ from one system to the other.

2. The metasomatic pathways observed in Northern Norrbotten deposits differ in part from those observed in other well-studied IOCG districts, such as Olympic Dam and the GBMZ. This is evidenced by the fact that the intensity of Ca-Fe and K-Fe alteration facies overprinting earlier formed albitite has not completely obliterated the albitite signature. Furthermore, the iron oxide content associated with K-Fe alteration is typically less intense than that observed in the majority of IOCG districts developed in felsic to intermediate volcanoplutonic environments while the high Mg contents is compatible to its increased availability due to the mafic-rich environment of the district and the common occurrence of skarn.

3. The IOCG-type Cu-Au mineralization in Northern Norrbotten is not systematically associated with brecciation and proximal K-feldspar rich K-Fe alteration. The Cu-Au mineralization also consists of i) massive magnetite-rich lenses that are hosted by skarn with proximal Ca-Fe alteration; and ii) magnetite disseminated in albitite with proximal K-Fe alteration.

4. The MIAC-related IOA and IOCG deposits in northern Norrbotten exhibit similarities to those in the Cloncurry district. These include early extensive Na to Na-Ca alteration, and HT Ca-Fe and K-Fe alteration overprinting albitites.

5. The Cloncurry district also hosts Cu-Au mineralization characterized by the development of early pervasive albitization, superimposed by Ca-Fe and K-Fe alteration, with sulfide phases playing a greater role in the mineralized zones.

6. The use of Na-Ca-Fe-K-Mg molar barcodes is a powerful approach that allows rapid discrimination of major metasomatic trends in MIAC mineral systems. This approach exhibits considerable promise for district-to-deposit scale exploration targeting.

7. Replacing the Mg component of the Na-Ca-Fe-K-Mg barcodes by (Al + Si)/10 helps discriminate between IOCG and porphyry deposits or at least highlight the need for a reassessment of the best deposit model. The lower contents of combined Si and Al of the Aitik deposit in the Norrbotten district than those of porphyry deposits offer new insights on the MIAC affinity of the Cu-Au mineralization.

### CRediT authorship contribution statement

**Olivier Blein:** Writing – original draft, Conceptualization. **Matthieu Harlaux:** Writing – review & editing. **Louise Corriveau:** Writing – review & editing. **Tero Niiranen:** Writing – review & editing. **Edward P. Lynch:** Writing – review & editing, Conceptualization. **Vladimir Lisitsin:** Writing – review & editing. **Kathy Ehrig:** Validation, Resources. **Jean-François Montreuil:** Writing – review & editing. **Blandine Gourceral:** Writing – review & editing, Project administration.

### Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence
the work reported in this paper.

## Data availability

Data will be made available on request.

## Acknowledgements

This research was made possible by financial support from the European Union's Horizon Europe research and innovation program under Grant Agreement No. 1010557357, EIS – Exploration Information System (https://eis-he.eu). It was conducted in collaboration with the Targeted Geoscience Initiative program of Natural Resources Canada. We would like to express our gratitude for Dr. Isabelle McMartin for her invaluable contribution as an internal reviewer of the manuscript. This article benefited from the constructive comments of anonymous reviewers, as well as editorial work by Stefano Albanese, which helped to improve the quality of the manuscript.

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