# Evaluating the role of ore metamorphism and deformation in the remobilization of critical metals during orogens formation

Alexandre Cugerone, Bénédicte Cenki-Tok

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Alexandre Cugerone, Bénédicte Cenki-Tok. Evaluating the role of ore metamorphism and deformation in the remobilization of critical metals during orogens formation. Ore Geology Reviews, 2025, 186, pp.106904. 10.1016/j.oregeorev.2025.106904. hal-05317139

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Review

# Evaluating the role of ore metamorphism and deformation in the remobilization of critical metals during orogens formation

Alexandre Cugerone<sup>a, ∗</sup>, Bénédicte Cenki<sup>b, †</sup>

ARTICLE INFO

Keywords:

Orogenic minerals

Critical metals

Metamorphism

Orogenesis

Germanium

Cobalt

Platinum-group elements

A B S T R A C T

Orogenic processes, including metamorphism and deformation, can significantly impact the interpretation, un-
derstanding and economic value of mineral deposits. Critical metals and metalloids (CMs) such as gallium (Ga),
geranium (Ge), indium (In), platinum group elements (PGE), and cobalt (Co) are commonly mined as by-
products of base metals (i.e., Zn, Fe, Cu, Ni). The impact of metamorphism on CMs (re)distribution is
frequently overlooked, underestimated or not investigated by adequate and representative analytical procedures.
In this review article, we evaluate the importance of metamorphism and deformation on the remobilization of
CMs. The timing of ore emplacement relative to orogen formation, mineralogy and ore textures of ca. 170 de-
posits reported in the literature have been extracted in three continental districts (Australia, China, and Europe).
This synthesis shows that metamorphism frequently overprints ore deposits and might create favorable condi-
tions for the redistribution of CMs within ore minerals. Orogenic minerals rich in CMs can be broadly defined as
the large-scale remobilization or sample-scale redistribution product of pre-existing CMs concentrations, present
in the primary ore, driven by metamorphism and/or tectonic processes. Contrasting behaviors for the formation
of orogenic minerals rich in CMs is described in the literature. Under low- to medium-grade conditions (<450 °C;
<2-3kbar), Ge-rich orogenic minerals are generally well preserved while In, Co-PGE-rich orogenic minerals form
newly at higher temperature (> 450 °C). In several sulfides potentially rich in CMs, experimental and natural
observations have demonstrated ductile behavior at low grades (~100-200 °C; <2kbar), which may affect the
distribution of CMs in sulfide ore. This review highlights the challenges ore geologists face in apprehending
primary signatures in sulfide minerals within systems affected by secondary orogenic events as well as the po-
tential of CMs system analysis in understanding the conditions of ore (de)formation.

**1. Introduction**

As the world shifts away from fossil fuels, the production of a large
number of wind turbines, solar panels, electric vehicles and batteries
will be essential to meet the demands of a society striving to reduce its
carbon footprint and manage energy consumption effectively (Hund
et al., 2020). The demand for the critical metals and metalloids (CMs)
needed to build such equipment will therefore increase substantially (e.
g. Vidal et al. 2013). Consequently, securing access to CMs is essential to
build a sustainable low-carbon economy. Indeed, indium, gallium, and
geranium are used in the production of solar panels and optic fibers.
Cobalt and lithium are used in batteries. Rare earth elements (REE) are
essential to build the powerful magnets used in wind turbines and
electric cars, and platinum-group elements are key components of

catalytic converters and many electronic systems. We are on the cusp of
a CMs boom and therefore it is essential to rethink and adapt our
approach to exploration and mining of these critical and strategic re-
sources, otherwise the looming supply shortage in the coming decades
will lead to a range of geopolitical, economic, and environmental issues
(Calderon et al., 2020).

A pivotal area of research focuses on uncovering the geological
processes that mobilize and concentrate CMs in the Earth's crust, which
helps locate resources and better understand conditions of formation
and deformation of the ore. Recent studies have shown that some CMs
are often associated with base metal ore deposits (e.g. Ge or Co can be
associated with Zn ores; Huston and Brauhart 2017; Erlandsson et al.
2023; Mudd et al. 2024; Fig. 1). While the primary sedimentary,
magmatic and hydrothermal processes (including alteration processes)

<footnote><sup>a</sup> Department of Earth Sciences, University of Geneva, Geneva, Switzerland</footnote>

<footnote><sup>b</sup> Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France</footnote>

<footnote>* Corresponding author.
E-mail address: benedicte.cenki@umontpellier.fr (B. Cenki).</footnote>
<figure><img src="image_3.png" /></figure>

**Fig. 1.** A wheel of element association illustrating the critical metals and metalloids discussed in this article, classified according to their geochemical characteristics: chalcophile, siderophile and lithophile (modified from Nassar et al. 2015). Main metals form the inner circle and associated elements appear in the outer circles proportional to their degree of primary production as by-product of the corresponding main metal.

by which these deposits form have been studied for decades, many deposits are located in ancient orogens, where the impact of recrystallization linked to metamorphism and tectonics is significant but can be

overlooked in economic geology (Tomkins, 2007; Goodenough et al., 2016; Spandler et al., 2020). Furthermore, there is a need for more detailed study of how CMs associated with base metal deposits are affected by these different processes (e.g. Cugerone et al. 2020, 2021 for Ga, Ge, In; Sayab et al. 2025 for Co).

Economic geologists generally focus on the primary magmatic, hydrothermal or sedimentary signature of ore deposits, following pre-existing genetic models and conventional exploration tools. The key secondary processes related to metamorphism and deformation that may remobilize and concentrate CMs are less systematically addressed. Primary deposits may be localized in orogenic belts and formed before, during and after orogenesis and this article focuses on the processes that may have affected primary deposits during orogenic event(s) (Fig. 2). This article is divided into three parts to evaluate the effects of metamorphic and tectonic processes on CMs mobility based on a literature review of ca. 170 deposits located in Australia, Europe and China: (i) an overview of key CMs and the types of primary base metal deposits they are associated with. A definition of orogenic minerals will be proposed, highlighting the main variables ruling metamorphic processes (pressure, temperature, fluid circulation); (ii) the different scales of mobility of these elements will be reviewed and a general model for remobilization of CMs will be proposed; (iii) finally, the role of metamorphic processes on the remobilization of CMs will be illustrated with a non-exhaustive list of examples for the discussed CMs.

## 2. Methodology

Deposits rich in CMs commonly occur in ancient orogens, but their relationship to orogenic events depends on relative timing. Some deposits form prior to the orogenic event, in geological settings that are likely to be subsequently affected by orogenesis – for example, VHMS deposits, which are commonly interpreted to form in oceanic crust and later become obducted during orogenic event(s) (Fig. 2). Some deposits

<figure><img src="image_4.png" /></figure>

**Fig. 2.** Simplified geodynamic cross-sections showing the main geological environments for the concentration of Cu, Pb and Zn-rich sulfides potentially hosting Ge, Ga, In, Co, PGE. (abbreviations: SEDEX = sedimentary exhalative; MVT = Mississippi Valley-Type; VHMS = Volcanic-hosted massive sulfide). The lower cross-section illustrates the main areas of metamorphic gradients along with their associated tectonic regimes.
form during the orogenic event (subduction and/or collisional events) – this is true for orogenic gold and many polymetallic vein deposits. And finally, some deposits may be localized in the orogenic belt but formed at the post-collisional stage – this is typically associated with hydrothermal polymetallic deposits.

In this study, we have created a database of ca. 170 deposits based on literature data with deposits located in three continental districts: Australia, China and Europe (75, 50 and 45 localities respectively; Extended supplementary material-1 and Extended supplementary material-2). These data are reported on the maps and histograms of Figs. 3–6 that show the location of these deposits or occurrences with respect to metamorphic conditions and/or orogenic provinces for Australia, Europe and China, respectively. For each deposit, we extracted geological and economic information from the existing literature as part of our methodology. We have reported the type of deposit, geological setting (structural domain, location), estimated resources (ore tonnage, metal grade, estimated CMs grade, estimated metal tonnage; Fig. 4), the probable relationship between ore formation and orogen, the primary setting of mineralization emplacement and age when available. For each deposit, the metamorphic grades are reported and for simplification purposes, are divided in four categories composed of: i) pervasive low grade (up to upper-greenschist facies); ii) pervasive high-grade (amphibolite, granulite facies), iii) no deformation or only

localized (shear-bands); iv) no consistent textural study to assess deformation imprint. Hydrothermal alterations occurring simultaneously with ore-body emplacement (i.e., albitization, chloritization, potassic) are not considered as metamorphism in this paper.

For some deposits such as Huize (Pb-Zn(–Ge) deposit in South China), studies differ regarding the impact of metamorphism on the ore (Han et al., 2007; Niu et al., 2024) posing a potential challenge in determining whether most of the deposit and sulfide mineralization have undergone deformation. Furthermore, in all these study cases, a significant issue arises regarding the representativeness of sampling methods, as most studies typically rely on only a few hundred samples. This limited sampling could have important weaknesses for evaluating the metamorphic imprint and potential remobilization across the entire scale of sulfide mineralization, which can extend up to several kilometers. Processes such as shearing and recrystallization, while crucial for understanding the relationship between deformation and ore formation, are often highly localized and typically confined to meter-scale structures such as faults, fold hinges, or shear zones.

Following this consideration, careful understanding about the more reliable and representative study for each deposit has been done in these cases. Basic description of the metamorphic ore texture and the occurrence of orogenic minerals rich in CMs are also reported in the ESM1. Using these data, we have estimated the relative proportions of ore and

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Simplified tectonic map of Australia with the occurrences of seventy-five base metal deposits hosting critical metals and metalloids (modified from Geosciences Australia's WMS map server service). The main deposits are reported following Huston and Brauhart (2017) and Mudd et al. (2018). For each deposit, the metamorphic grade is estimated based on published literature (low grade = up to upper greenschist conditions). A related timescale is shown below the map where deposits with their primary mineralization emplacement are replaced according to orogenic events (see detail in the ESM1). Proportions of metal tonnage for the two groups of critical metals and metalloids are represented in histograms to compare the four categories of ore.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>Fig. 4. Relative proportion for ore and metal tonnage in the two groups of critical metals and metalloids and in the four categories evaluating the impact of metamorphism on ore: i) pervasive high-grade (amphibolite, granulite facies); ii) pervasive low grade (up to upper-greenschist facies); iii) no deformation or only localized (shear-bands); iv) no consistent textural study to assess deformation imprint. Ore and metal tonnages for each category are mentioned on the X-axis to give an approximative estimation based on data given in the literature (the reader is referred to ESM1 for references).</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Simplified geological map of Europe with the occurrences of forty-five deposits hosting critical metals and metalloids (modified from the European Geology Online portal http://www.europe-geology.eu and the corresponding WMS map server and Faure and Ferrière 2022). For each deposit, the metamorphic grade is estimated based on published literature (low grade = up to upper greenschist conditions). A related timescale is shown below the map where deposits with their primary mineralization emplacement are replaced according to orogenic events (see detail in the ESM1). Proportions of metal tonnage for the two groups of critical metals and metalloids are represented in histograms to compare the four categories of ore.</figcaption></figure>

metal tonnage across the four metamorphic categories and within the three continental districts.

### 3. Critical elements and orogens

Metals and metalloids which are economically important and present a high supply risk are considered critical (European Commission, 2020). In this article, the EU nomenclature is followed. It does not differ significantly from the US or Australian classification (U.S. Geological Survey, 2023; Mudd et al., 2024). The focus will be on a few elements, classified according to their geochemical affinities. They are associated with well-known types of base metal deposits (Nassar et al. 2015; Fig. 2) and have been systematically and consistently integrated in this list for the past decade. These elements are:

- gallium (Ga), indium (In) and germanium (Ge), which are mainly chalcophile elements generally associated with lead, zinc, copper, tin (Fig. 1) or in the case of Ga, also with aluminum (bauxite).

- cobalt (Co) and the platinum-group elements (PGEs) which are mainly siderophile and chalcophile elements commonly associated with copper, nickel, or platinum deposits (Fig. 1).

#### 3.1. Do we have a genetic link between orogen and ore deposits?

Orogens form as a consequence of converging plate boundaries. The evolution stages of orogens (subduction, collisional) and the type of orogens (cold or hot; Jamieson and Beaumont 2013) can be key factors influencing the (re)mobilization of metals in the crust. During the evolutionary stage of orogens, subduction related orogens are generally rich in Cu and moderately in Pb-Zn (porphyry/polymetallic systems and skarn systems; Fontboté et al. 2017). At the collisional and post-collisional stage, limited amount of Cu-rich porphyry systems are documented (Hou and Cook, 2009). In terms of orogen type, cold orogens related to a low thermal gradient (< 10 °C/km) are generally poor in metals (i.e., Alpine orogeny) but hot orogens (Himalaya, Variscan,
<figure><img src="image_8.png" /><figcaption>**Fig. 6.** Simplified tectonic map of China with the occurrences of fifty deposits hosting critical metals and metalloids (modified from Deng et al. 2017). For each deposit, the metamorphic grade is estimated based on published literature (low grade = up to upper greenschist conditions). A related timescale is shown below the map where deposits with their primary mineralization emplacement are replaced according to orogenic events (see detail in the ESM1). Proportions of metal tonnage for the two groups of critical metals and metalloids are represented in histograms to compare the four categories of ore.</figcaption></figure>

Andes) with higher thermal gradient (20–30 °C/km; Jamieson and Beaumont 2013; Zhang et al. 2022; Faure 2023) host higher quantities of metals, probably related to intense magmatism and fluid circulation in the crust. The formation of orogens triggers new input of metals in the crust related to magmatism and may mobilize pre-existing metal and fluid concentrations in the crust during metamorphism (Leach and Rowan 1986; Fig. 2). Orogenic processes can affect various types of deposits, from Mississippi Valley-type to volcanic hosted massive sulfides and porphyry deposits, depending on the tectono-metamorphic evolution of the terrane hosting the mineralization, although some deposits may form synchronously with orogeny (Fig. 2).

The primary formation of base metal deposits (in which CMs can be found as co-products) are commonly interpreted in terms of hydrothermal processes occurring in sedimentary basins or magmatic processes that may be overprinted by late hydrothermal events (for example Jébrak and Marcoux 2008; Wilkinson 2013; Horn et al. 2021). This section offers a short introductory overview of the main primary processes involved:

Lead-Zinc ores may contain Ga, Ge and In contents and are usually considered to mainly form in sedimentary basins and consist mostly of very large sediment Pb-Zn deposits commonly close to cratonic edges and the interface between thick and thin lithospheres (Hoggard et al.,

2020; Huston et al., 2023). Alternatively, volcanic-hosted massive sulfide (VHMS) deposits are significant sources of base (Zn, Pb, Cu) and precious (Au, Ag) metals and are believed to be linked to sub-seafloor formation processes, although many of their primary features have been overprinted by intense metamorphism (Shanks and Thurston, 2012; Hollis et al., 2015; Rincon et al., 2025).

In sediment-hosted Pb-Zn deposits, different models associated with extension or shortening exist like Mississippi Valley Type (MVT, Leach and Rowan 1986; Wilkinson 2013), sedimentary exhalative (SEDEX, Wilkinson 2013), carbonate-replacement (Spinks et al., 2021), Mount Isa type (MIT, Cave et al. 2022) or Broken Hill type (BHT, Spry and Teale 2021) but the main factor is the mobilization of large quantities of internal or external fluids that contains Pb, Zn, Cu, Ag, F, Ba among other elements within sedimentary basins. During or immediately after orogen formation, the gravity driven lateral flow is frequently documented as an important continental scale mechanism to form base metal deposits in basins, especially Mississippian Valley-type deposit in the US (Leach and Rowan, 1986; Wilkinson, 2013), in South China and in Western Europe (Leach and Rowan, 1986; Wilkinson, 2013; Song et al., 2023). These Pb-Zn mineralizations are typically rich in Ge and Ga (Belissont et al., 2014; Luo et al., 2022; Frenzel et al., 2024; Niu et al., 2024; Luo et al., 2025). However, the timing of MVT deposits and the gravity-driven lateral flow
model is disputed in many base metal deposits, as geochronological data and structural/textural evidence often indicate alternative formation processes (Muchez et al., 2005; Giorno et al., 2022; Tavazzani et al., 2024). Similarly, in Australia, the question of far-field conditions raises between systems considered to have formed in extension (typical SEDEX model; Huston et al. 2006; Wilkinson 2013) and deposits formed during shortening periods, by carbonate replacement (Spinks et al., 2021). In South China, carbonate-hosted Pb-Zn mineralization, are generally contemporaneous to three orogenic periods (Late Yanshanian, Late Indosinian and Caledonian-Hercynian; e.g. Luo et al. 2023) but their context of emplacement and the main geodynamic drivers (shortening, extension) are still debated. In external orogenic domains, the presence of faults and shear zones plays a major role in controlling fluid pathways. Hydrostatic pressure often dominates over lithostatic pressure leading to the formation of metal-rich veins and breccia (Perkins, 1997). Reviewing the mode of formation of Pb-Zn systems in detail is beyond the scope of this paper as there are several excellent works in that space (e.g. Leach 2005; Huston et al. 2006).

Nickel-Cu(-Cr-Fe) hypogene ores potentially host Co and PGE and are found in magmatic sulfide deposits, IOCG deposits and as a by-product of copper, particularly in sediment-hosted Ni-Cu deposits (Horn et al., 2021). More commonly, Co can be concentrated in large layered mafic-ultramafic intrusions in intracontinental settings (Holwell et al., 2019). Generally, the magmatic processes that concentrate these metals are directly linked to fractional crystallization and sulfide saturation. Mineral phases with higher density that crystallize early in the sequence (like chromite, olivine or ilmenite for example) segregate and concentrate at the base of the magma chamber upon gravitational processes (Schulz et al., 2014; Horn et al., 2021). Ore rich in PGE can be found in sulfur - nickel ores that have formed by magmatic immiscibility after various degrees of mantle partial melting (Schulz et al., 2014). In most cases, the main PGE mineral hosts are presently poorly known and understood (Maier, 2005). Recently, orogenic Co-Au rich deposits were reported in Paleoproterozoic rocks of Finland and North-East China (Tian et al., 2024; Sayab et al., 2025) with clear association between tectonics, metamorphism and veining.

Some critical non-metallic elements (C, Li, Ta) are considered to form specifically in metamorphic environments but will not be further considered in this article. Graphite is formed in metamorphic rocks in which organic matter has been transformed to graphite at upper greenschist to granulite facies conditions (Beyssac and Rumble, 2014). As an example, Cui et al. (2017) show that the numerous graphite mines in China can be linked to different metamorphic context. Several CMs, including lithium and tantalum, may locally occur in pegmatites, which are melts derived from the partial melting of the crust (Linnen et al., 2012; Müller et al., 2022; Knoll et al., 2023). The processes leading to the formation of these rocks are at the limit between magmatic and supra-solidus metamorphic processes. In this article, the focus will be on the effects of sub-solidus metamorphic recrystallization and deformation occurring during orogenesis. Other CMs such as REE are generally associated with carbonatite magmas at post-collisional stage. Possible significant metamorphic imprint is reported in several REE deposits, among them, the giant Bayan-Obo REE-Nb deposit (Smith et al., 2015). However, the amount of data showing evidence of REE remobilization during orogen formation is presently limited and the role of orogenic processes on the REE remobilization is beyond the scope of this review article.

## 3.2. Basic understanding of domains rich in critical elements within the three continental districts

### 3.2.1. Australia

In Australia, Archean, Proterozoic and Paleozoic rocks host several giant or world-class ore deposits (Fig. 3), making most of the country's mineral resources (Pirajno and Bagas, 2008). These are associated with intraplate tectono-metamorphic extensional events or orogenic

reworking during collision and crustal thickening. Gallium, Ge, and In are generally associated with Pb-Zn deposits (Huston et al., 1995; Huston et al., 2006; Cook et al., 2009; Huston and Bastrakov, 2024). Whatever their initial mode of formation, several Pb-Zn deposits are located in orogens (Fig. 3), and our work shows that low or high-grade metamorphic recrystallization is observed for at least 65 % of the relative proportion of total ore tonnage (Fig. 4A). Additional minor In occurrences are reported in other settings (e.g. shale of Mt Isa, Sn-bearing granite deposits in Tasmania) that are also located in orogens.

Cobalt and PGE deposits are mostly located in mafic-ultramafic rocks in Western Australia, as by-products of Ni-Cu ores (e.g., Munni Munni in the Archean Pilbara craton, Panton in the Proterozoic Halls Creek orogen, Hoatson et al. 2014; Beinlich et al., 2020). These intrusions were likely emplaced into an intraplate setting and the mineralization is largely magmatic, even if some (5 out of 17 localities) have been subsequently deformed and metamorphosed in orogenic belts (< 5 % of the relative proportion for Co ore and metal tonnages experienced metamorphism; Fig. 4A). Other potential sources of Co in Australia include Cu-deposits in metasedimentary rocks (Mt Isa and Mt Oxide in Proterozoic orogens; Croxford 1974), Cu-rich VHMS deposits (Tritton NSW in the Phanerozoic Lachlan orogen, DeGrussa WA) and IOCG deposits (Ernest Henry, Skirrow 2022).

### 3.2.2. Europe

In Europe, the numerous Ge, Ga, and In occurrences are associated with Pb-Zn deposits located in remnants of the Variscan or Paleoproterozoic belts, such as the ones in Germany, France, Spain and Scandinavia (Fig. 5, Munoz et al., 1994; Moura, 2008; Bauer et al., 2019; Rincon et al., 2025). As an example, in the Western part of Europe, some deposits underwent no deformation such as the Saint-Salvy Pb-Zn(-Ge) mine (Munoz et al. 1994; Belissont et al. 2014) whilst others underwent low to high grade deformation such as most of the Iberian Pyrite belt Pb-Zn-Cu deposits (Reiser et al., 2011; Carvalho et al., 2018). At least 63 % of the total relative Zn + Pb tonnage of our database in Europe show indications of low and high-grade metamorphic recrystallization (Fig. 4B and 5 with tables in ESM1).

Base metal deposits rich in PGE are relatively rare and small in Europe (Fig. 5) and are mostly located in mafic-ultramafic complexes in Precambrian cratons of Scandinavia (Santaguida et al., 2015; Moilanen et al., 2021). Even though the initial enrichment in PGE is magmatic, the authors highlight the importance of post-magmatic processes remobilizing PGE in shear zones in these polymetamorphic terranes. The review of Co deposits (Horn et al., 2021) shows that most Co deposits in Europe are located in Proterozoic deformed basement rocks of Scandinavia and locally in the Alpine Orogenic Belt of Western Europe. These Co deposits are located in orogens and therefore, depending on timing of formation of the primary deposit, might have been reworked during secondary metamorphism and deformation (e.g. Vasilopoulos et al. 2021). Recently in Finland, orogenic Co-Au rich deposits were reported at Rajapalot (Sayab et al., 2025), showing metamorphic Co mineralization mostly associated with pyrite in dilated fold hinges.

### 3.2.3. China

In China, a large number of Pb-Zn deposits hosting significant Ge-Ga-In concentrations are found in South China craton, mostly in Paleozoic and Mesozoic rocks (Fig. 6). A lot of these deposits hosted in sedimentary basins are probably genetically associated with large fluid migration during orogenic events (Caledonian, Indosinian, Yanshanian) and most of them are considered as MVT and/or carbonate-hosted deposits, especially in the Sichuan-Yunnan-Guizhou metallogenic belt (SYG; Hu and Zhou 2012; Hu et al. 2017; Leach and Song 2019; Luo et al. 2023; Song et al. 2023). However, these carbonate-hosted deposits may present recrystallization features that record the deformation imprint on the ore such as the world class Huize or the Mengxing deposit ((Han et al., 2007; Jia et al., 2023). In highly deformed marble and volcanic sediments, the Xitieshan Pb-Zn deposit (Zhao et al., 2021) and the
Keketale Pb-Zn deposit (Zheng et al., 2013; Liu et al., 2024) host metamorphosed sulfides such as sphalerite and pyrite which locally host microscale In-rich minerals (Zhao et al., 2021). If we consider that the textural description in these studies is representative of the whole studied deposit, about 50 % of the relative Zn-Pb ore and metal tonnage in China is affected by low and high-grade metamorphism (Fig. 4C).

Cobalt and PGE resources are frequently deformed in China (90 % of the relative tonnage; Fig. 4C). These deposits have endured moderate to high-grade reworking with some CMs redistribution locally reported (Song et al., 2003; Han et al., 2020). Similarly to a Co-Au-rich deposit reported in Paleoproterozoic rocks of Finland (Sayab et al., 2025), Co-Au-rich ore is observed in orogenic veins, probably showing the wide-spread occurrence of Co-Au rich ore in old orogens (Paleoproterozoic; Tian et al., 2024).

### 3.3. Definition of orogenic minerals

As described above, different types of mineralization may form in orogenic belts, before, during and after orogenesis. However, it is now well established that metamorphic processes are key to the mobility of chemical elements in orogenic contexts (e.g. Tomkins 2013 for gold, McGloin et al. 2016 for U-REE-Zr mineralization, Qiu et al. 2021 for cobalt). The lessons learnt from the mobility of elements during metamorphic processes will contribute to define "orogenic minerals as newly formed minerals resulting from orogenic processes, including deformation, static or dynamic recrystallization, and the influence of metamorphic fluids.".

The mineralogical changes associated are one of the primary controls on CMs mobility. These changes may either contribute to an upgrading of the ore grade or simply redistribute CMs at sample scale, potentially into phases that may be more or less amenable to processing for extraction of the CMs (see the exhaustive mineral list for Ge, Ga, In and Co in Table 1). Metamorphic processes depend on the intertwined action of intensive parameters that include temperature, pressure, deformation, fluid (oxidation state) and protolith bulk chemistry (Yardley, 2005; Yardley and Bodnar, 2014).

Regional *temperature and pressure* gradients enhance recrystallization, favor reaction kinetics and the release of fluids. Ultimately, regional metamorphism can lead to partial melting and melt loss during granulite facies metamorphism and can play a role in both increasing the concentration of metals in the melt and/or the residue and increasing grain size (e.g. Tomkins and Mavrogenes 2003; Morrissey et al. 2016). In addition, regional metamorphism is generally associated with tectonics, and therefore, with gradients of deformation that may localize within faults and shear zones (Yardley and Bodnar, 2014). These are not only preferential pathways for fluid circulation (as they present an enhanced porosity), but dynamic recrystallization itself may trigger the mobility and remobilization of metals (Cugerone et al., 2020). *Bulk rock chemistry* and the primary bulk chemical content in CMs may not be altered by metamorphism (Tomkins, 2007). These examples are developed in section (4) and (5). *Dynamic recrystallization* associated with localized deformation may be responsible for the formation of accessory phases enriched in CMs and section (5) will develop examples illustrating this process.

*Metamorphic fluids* play a key role in the mobility of CMs. For example, the mobility of CMs can be triggered by low to highly saline orogenic fluids, generally rich in CO₂ and circulating in shear zones and deformed rocks under greenschist facies conditions. *Morrissey and Tomkins* (2020) highlight the origin of highly saline metamorphic fluids (>20 wt% NaCl), which can favor the mobility of CMs in orogenic belts. The presence of evaporites in early orogenic setting might enhance the formation of Cl-rich metamorphic fluids and trigger the formation of a large range of syn-orogenic magmatic-metamorphic ore deposits like Fe oxide Cu-Au, Fe sulfide Cu-Au, Mo-Re and U-REE (*Morrissey and Tomkins*, 2020). As a consequence, these base metals and the associated CMs are expected to migrate in orogenic settings when highly saline fluids are

available. Fluids may also be released by metamorphic reactions (dehydration, decarbonation), and their associated oxygen or sulfur fugacity are major parameters that control the thermodynamic stability of mineral assemblages containing enrichment in Ge (e.g. Bernstein 1985; Sahlström et al. 2017; Skirrow 2022 for Ge that is either stabilized in oxides or sulfides).

## 4. Scales of critical elements mobility

### 4.1. Geodynamics and plate tectonic scale drivers of ore deposit formation

Understanding the thermal evolution of the crust during orogenesis is a pre-requisite to unravel the factors that will drive element mobility at different scales (from km- to mm-scale). Heat and fluid transfer are key drivers that can initiate or enhance ore formation during metamorphism. Similar to the mineral systems approach (Mccuaig et al., 2010), these drivers require a network of crustal- and lithospheric-scale permeability pathways and traps from source-to-sink that are controlled by tectono-metamorphic processes. As a consequence, tectono-metamorphic processes may produce local to continental-scale fluid flow which could be the main driver for the formation of base metals and CMs in orogen-related basins (Oliver et al., 2006).

Temperature plays a major role in controlling crustal and lithospheric rheological characteristics and heterogeneities that drive fluids flow and mass transfers. In particular, the distribution of radiogenic heat production in the crust, mainly reworked by magmatism and erosion, controls the geotherm (Mareschal and Jaupart, 2013), drives heat flow pathways, and governs the conditions for ore formation. Zoning in metal content is frequent at orogen scale from more Cu-rich and relatively Pb-Zn poor areas in the core of orogens (magmatic porphyry-style and epithermal mineralization; Fontboto et al. 2017) but limited information exists on the potential zoning of CMs such as Ga, Ge, and In at the scale of an orogen and/or depending on geological setting. Collisional orogens have long been recognized for favoring the appearance of (giant) ore deposits (Laznicka, 2014; Zhang et al., 2022). This is because these have geodynamic settings with intense crust-mantle interaction, implying both convective and conductive heat flow, which leads to injection of fertile material into the accessible crust (e.g. Vigneresse 2019). Classically, the orogenic model involves fluid circulation driven by heat and decompression. As an example, numerical models coupling deformation, heat transfer, and porous fluid flow can be implemented at orogenic scale in order to decipher the interaction between these key parameters at tectonic/regional scale and their control on ore formation (e.g. Oliver et al. 2006; Glerum et al. 2024).

### 4.2. Metamorphic regional gradients as drivers of critical elements redistribution in orogenic minerals

Metamorphic processes may influence the distribution and remobilization of CMs in orogenic minerals through two primary mechanisms: (1) formation of new deposits, and (2) modification of existing deposits through overprinting processes, potentially leading to CMs redistribution and/or remobilization. Generally, the distribution of elements is controlled by the thermodynamic stability of their host minerals (Yardley and Cleverley, 2014), and this is also valid for CMs. Little attention has been paid to the newly-formed accessory critical minerals that have concentrated CMs in response to the changing pressure-temperature-fluid conditions. Pitcairn et al. (2010) have shown that the concentration of chalcophile elements (like Au, Ag, As, Hg, Mo, Sb) depend on the thermodynamic stability of sulfides (e.g. pyrite, pyrrhotite) during the changing thermodynamic conditions associated with prograde metamorphism. In the unmetamorphosed rock, pyrite is stable, but at greenschist facies conditions, it recrystallizes into pyrrhotite which is depleted in Au, Ag, As, Hg, Mo and Sb that are therefore remobilized into newly formed cobaltite, galena and sphalerite. At amphibolite facies, these three mineral phases break down releasing the
<caption>**Table1**</caption>

Compilation of germanium, indium, gallium and cobalt minerals, reporting the ideal chemical formula and elemental content for Ge, Ga or In. The minerals in red are the most frequently observed, even if their occurrence remains rarely observed for each ore systems. A list of PGE minerals is not provided due to the poorly constrained nature of their mineralogy and occurrence.

<table><thead><tr><th colspan="5">Germanium minerals</th></tr><tr><th>Mineral group</th><th>Name</th><th>wt.% Ge</th><th>Formula</th><th>Example in the literature</th></tr></thead><tbody><tr><td>Germanates</td><td>Bartelkeite</td><td>36</td><td>PbFeGe<sup>6+</sup>(Ge<sup>4+</sup>O<sub>8</sub>)</td><td>Origlieri et al., 2012</td></tr><tr><td>Germanates</td><td>Carboirite</td><td>25</td><td>FeAl<sub>2</sub>GeO<sub>5</sub>(OH)<sub>2</sub></td><td>Johan et al., 1983</td></tr><tr><td>Germanates</td><td>Ge-lepidomelane</td><td>28</td><td>(K,Na,H<sub>3</sub>O)<sub>2</sub>(Fe<sub>6</sub>)(Ge<sub>5</sub>Al<sub>3</sub>)<sub>0</sub>2(Cl<sub>2</sub>OH<sub>2</sub>)</td><td>Johan et al., 1983</td></tr><tr><td>Germanates</td><td>Otjisumeite</td><td>45</td><td>PbGe<sub>4</sub>O<sub>9</sub></td><td>Keller et al., 1981</td></tr><tr><td>Hydroxides</td><td>Manganostottite</td><td>35</td><td>MnGe(OH)<sub>6</sub></td><td>Strunz et al., 1961</td></tr><tr><td>Hydroxides</td><td>Stottite</td><td>32</td><td>FeGe(OH)<sub>6</sub></td><td>Strunz et al., 1958</td></tr><tr><td>Oxides</td><td><strong>Argutite</strong></td><td>69</td><td>Ge<sup>4+</sup>O<sub>2</sub></td><td>Johan et al., 1983</td></tr><tr><td>Oxides</td><td><strong>Brunogeierite</strong></td><td>22</td><td>(Fe<sup>2+</sup>)<sub>2</sub>Ge<sup>4+</sup>O<sub>4</sub></td><td>Otteman & Nuber, 1972</td></tr><tr><td>Oxides</td><td>Eyselite</td><td>54</td><td>Fe<sup>3+</sup>Ge<sup>3+</sup>O<sub>7</sub>(OH)</td><td>Roberts et al., 2004</td></tr><tr><td>Oxides</td><td>Krieselite</td><td>24</td><td>Al<sub>2</sub>GeO<sub>4</sub>(F<sub>2</sub>OH)<sub>2</sub></td><td>Schlüter et al., 2010</td></tr><tr><td>Pallado germanide</td><td>Marathonite</td><td>25</td><td>Pd<sub>2</sub>Ge</td><td>McDonald et al., 2017</td></tr><tr><td>Silicates</td><td>Mathewrogersite</td><td>3</td><td>Pb<sub>7</sub>(Fe,Cu)Al<sub>3</sub>Ge [(Si<sub>6</sub>O<sub>18</sub>)<sub>2</sub>](OH, H<sub>2</sub>O)<sub>6</sub></td><td>Keller & Dunn, 1986</td></tr><tr><td>Sulfates</td><td>Cararaite</td><td>15</td><td>Ca<sub>3</sub>Ge(OH)<sub>6</sub>(SO<sub>4</sub>)(CO<sub>3</sub>)·12H<sub>2</sub>O</td><td>Merlino et al., 2001</td></tr><tr><td>Sulfates</td><td>Fleischerite</td><td>7</td><td>Pb<sub>3</sub>Ge[(OH)<sub>6</sub>(SO<sub>4</sub>)<sub>2</sub>]·3H<sub>2</sub>O</td><td>Frondel et al., 1960</td></tr><tr><td>Sulfates</td><td>Itoite</td><td>8</td><td>Pb<sub>3</sub>[GeO<sub>2</sub>(OH)<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>]</td><td>Frondel et al., 1960</td></tr><tr><td>Sulfates</td><td>Schaurteite</td><td>13</td><td>Ca<sub>3</sub>Ge[(OH)<sub>6</sub>(SO<sub>4</sub>)<sub>2</sub>]·3H<sub>2</sub>O</td><td>Origlieri et al., 2012</td></tr><tr><td>Sulfides</td><td>Alburnite</td><td>6</td><td>Ag<sub>8</sub>GeTe<sub>2</sub>S<sub>4</sub></td><td>Tamas et al., 2014</td></tr><tr><td>Sulfides</td><td><strong>Argyrodite</strong></td><td>6</td><td>Ag<sub>8</sub>GeS<sub>6</sub></td><td>Weisbach, 1886</td></tr><tr><td>Sulfides</td><td>Barquillite</td><td>17</td><td>Cu<sub>2</sub>(Cd,Fe)GeS<sub>4</sub></td><td>Murciego et al., 2014</td></tr><tr><td>Sulfides</td><td><strong>Briartite</strong></td><td>17</td><td>Cu<sub>2</sub>(Fe,Zn)GeS<sub>4</sub></td><td>Francotte et al., 1965</td></tr><tr><td>Sulfides</td><td>Calvertite</td><td>6</td><td>Cu<sub>5</sub>Ge<sub>0.5</sub>S<sub>4</sub></td><td>Jambor et al., 2007</td></tr><tr><td>Sulfides</td><td>Catamarcaite</td><td>8</td><td>Cu<sub>2</sub>GeWS<sub>8</sub></td><td>Putz et al., 2006</td></tr><tr><td>Sulfides</td><td><strong>Germanite</strong></td><td>6.0–11</td><td>Cu<sub>13</sub>Fe<sub>2</sub>Ge<sub>2</sub>S<sub>16</sub></td><td>Pufahl, 1922</td></tr><tr><td>Sulfides</td><td>Germanocolusite</td><td>10</td><td>Cu<sub>13</sub>(V,Ge,As)<sub>3</sub>S<sub>16</sub></td><td>Spiridonov et al., 1992 / Wagner & Monecke, 2005</td></tr><tr><td>Sulfides</td><td>Maikainite</td><td>11</td><td>Cu<sub>10</sub>(Fe,Cu)<sub>3</sub>MoGe<sub>3</sub>S<sub>16</sub></td><td>Spiridonov et al., 2003</td></tr><tr><td>Sulfides</td><td>Morozeviczite-Polkovicite</td><td>10</td><td>(Pb,Fe)<sub>3</sub>Ge<sub>1-x</sub>S<sub>4</sub></td><td>Harańczyk, 1975</td></tr><tr><td>Sulfides</td><td>Omariniite</td><td>12</td><td>Cu<sub>8</sub>Fe<sub>2</sub>ZnGe<sub>2</sub>S<sub>12</sub></td><td>Bindi et al., 2017</td></tr><tr><td>Sulfides</td><td>Ovamboite</td><td>10</td><td>Cu<sub>10</sub>(Fe,Cu,Zn)<sub>3</sub>WGe<sub>3</sub>S<sub>16</sub></td><td>Spiridonov et al., 2003</td></tr><tr><td>Sulfides</td><td>Putzite</td><td>8</td><td>(Cu<sub>4.7</sub>Ag<sub>3.3</sub>)<sub>8</sub>GeS<sub>6</sub></td><td>Paar et al., 2004</td></tr><tr><td>Sulfides</td><td><strong>Renierite</strong></td><td>8.0–9</td><td>Cu<sub>10</sub>(Zn<sub>1-x</sub>Cu)Ge<sub>2-x</sub>As<sub>x</sub>Fe<sub>4</sub>S<sub>16</sub></td><td>Vaes, 1948 / Bernstein, 1986</td></tr><tr><th colspan="5">Indium minerals</th></tr><tr><th>Mineral group</th><th>Name</th><th>wt.% In</th><th>Formula</th><th>Example in the literature</th></tr><tr><td>Hydroxides</td><td>Dzhalindite</td><td>69</td><td>In(OH)<sub>3</sub></td><td>Duan et al., 2024</td></tr><tr><td>Hydroxides</td><td>Yanomamite</td><td>69</td><td>(InAs<sub>0.4</sub>)·2(H<sub>2</sub>O)</td><td>Botelho et al., 1994</td></tr><tr><td>Native</td><td>Damiaoite</td><td>54</td><td>PtIn<sub>2</sub></td><td>Duan et al., 2024</td></tr><tr><td>Native</td><td>Yixunite</td><td>16</td><td>Pt<sub>3</sub>In</td><td>Duan et al., 2024</td></tr><tr><td>Sulfides</td><td>Sakuraiite</td><td>20–30</td><td>(Cu,Zn,Fe,<sub>1</sub>In,<sub>Sn</sub>)<sub>4</sub>S<sub>4</sub></td><td>Cook et al., 2011</td></tr><tr><td>Sulfides</td><td>Indite</td><td>56</td><td>FeIn<sub>2</sub>S<sub>4</sub></td><td>Duan et al., 2024</td></tr><tr><td>Sulfides</td><td>Petrukite</td><td>27</td><td>(Cu,Fe, Zn)<sub>2</sub>(Sn,In)<sub>4</sub>S<sub>4</sub></td><td>Radosavljevic et al., 2005</td></tr><tr><td>Sulfides</td><td>Cadmoindite</td><td>49</td><td>CdIn<sub>2</sub>S<sub>4</sub></td><td>Duan et al., 2024</td></tr><tr><td>Sulfides</td><td><strong>Roquesite</strong></td><td>35–47</td><td>CuInS<sub>2</sub></td><td>Jonsson et al., 2013</td></tr><tr><td>Sulfides</td><td>Laforêtite</td><td>37</td><td>AgInS<sub>2</sub></td><td>Meissier et al., 1999</td></tr><tr><th colspan="5">Gallium minerals</th></tr><tr><th>Mineral group</th><th>Name</th><th>wt.% Ga</th><th>Formula</th><th>Example in the literature</th></tr><tr><td>Hydroxides</td><td>Söhngente</td><td>58</td><td>Ga(OH)<sub>3</sub></td><td>Foley et al., 2017</td></tr><tr><td>Hydroxides</td><td>Tsumgallite</td><td>60</td><td>GaO(OH)</td><td>Foley et al., 2017</td></tr><tr><td>Phosphates</td><td>Gallobeudantite</td><td>15</td><td>PbGa<sub>3</sub>(AsO<sub>4</sub>)(SO<sub>4</sub>)(OH)<sub>6</sub></td><td>Foley et al., 2017</td></tr><tr><td>Sulfides</td><td><strong>Gallite</strong></td><td>35</td><td>CuGaS<sub>2</sub></td><td>Ueno et al., 2000</td></tr><tr><th colspan="5">Cobalt minerals</th></tr><tr><th>Mineral group</th><th>Name</th><th>wt.% Co</th><th>Formula</th><th>Example in the literature</th></tr><tr><td>Carbonates</td><td>Spherocobaltite</td><td>50</td><td>CoCO<sub>3</sub></td><td>Kloprogge et al., 2006</td></tr><tr><td>Carbonates</td><td>Kolwezite</td><td>18</td><td>(Cu,Co)<sub>2</sub>CO<sub>3</sub>(OH)<sub>2</sub></td><td>Perchiazzì et al., 2018</td></tr><tr><td>Phosphates</td><td>Erythrite</td><td>30</td><td>Co<sub>3</sub>(AsO<sub>4</sub>)<sub>2</sub>·8H<sub>2</sub>O</td><td>Cook, 2007</td></tr><tr><td>Selenides</td><td>Trogtalite</td><td>27</td><td>CoSe<sub>2</sub></td><td>Hu et al., 2025</td></tr><tr><td>Sulfates</td><td>Aplowite</td><td>16</td><td>(Co,Mn,Ni)SO<sub>4</sub>·4H<sub>2</sub>O</td><td>Jambor & Boyle, 1965</td></tr><tr><td>Sulfates</td><td>Moorhouseite</td><td>13</td><td>(Co,Ni,Mn)SO<sub>4</sub>·6(H<sub>2</sub>O)</td><td>Jambor & Boyle, 1965</td></tr><tr><td>Sulfides</td><td>Cattierite</td><td>48</td><td>CoS<sub>2</sub></td><td>Kerr, 1945</td></tr><tr><td>Sulfides</td><td><strong>Safflorite</strong></td><td>21</td><td>(Co,Fe)As<sub>2</sub></td><td>Radcliffe & Berry, 1968</td></tr><tr><td>Sulfides</td><td>Glaucodot</td><td>27</td><td>(Co,Fe)As<sub>2</sub></td><td>Yang et al., 2008</td></tr><tr><td>Sulfides</td><td>Skutterudite</td><td>18</td><td>(Co,Ni)As<sub>3</sub></td><td>Tarkian et al., 1983</td></tr><tr><td>Sulfides</td><td><strong>Cobaltite</strong></td><td>36</td><td>Cu(Co,Ni)<sub>2</sub>S<sub>4</sub></td><td>Saintilan et al., 2017</td></tr><tr><td>Sulfides</td><td><strong>Carrollite</strong></td><td>29</td><td>CuCo<sub>2</sub>S<sub>4</sub></td><td>Vaugitan et al., 1979</td></tr><tr><td>Sulfides</td><td>Linnaeite</td><td>58</td><td>Co<sub>3</sub>S<sub>4</sub></td><td>Vaugitan et al., 1979</td></tr><tr><td>Sulfides</td><td>Siegenite</td><td>15</td><td>(Ni,Co)<sub>3</sub>S<sub>4</sub></td><td>Imai et al., 1973</td></tr><tr><td>Sulfides</td><td><strong>Cobaltpentlandite</strong></td><td>67</td><td>Co<sub>9</sub>S<sub>8</sub></td><td>Liu et al., 2024</td></tr></tbody></table>

Mineral in bold = most frequent mineral in each system.
hosted trace elements that are, consequently leached from the rock by pervasive metamorphic fluids (Pitcairn et al., 2010). Similarly, Qiu et al. (2021) have shown that fluid-mediated pyrite dissolution and reprecipitation were responsible for Co release from syngenetic pyrite. In this example, geochronological results on apatite associated to the epigenetic Cu-Co mineralization indicate that the main mineralizing event is closely related to a deformation event that is syn- to post-peak metamorphism. Cobalt is released as pyrite deforms and recrystallizes during metamorphism. It precipitates in Co-rich minerals like cobaltite. In addition, fluid-assisted metamorphism can be a major supplier for Pb-Zn ore systems, and potentially for related critical elements (Ge, Ga, In).

Investigating the metal contents of minerals that follow a typical Barrovian gradient in a metasedimentary sequence, Hammerli et al. (2016) have shown that the mobility of base metals like Pb and Zn is controlled by the break-down of their mineral host (feldspar and micas, respectively) when temperature increases. Finally, metamorphic prograde break-down reactions in high grade metasedimentary sequences might contribute to CMs mobility with metasedimentary affinities (Li, Cs, Ta, Sn, W) and play a key role in controlling the content in CMs of their partially molten products (Kunz et al., 2022).

### 4.3. Regional structural controls on deposits formation and potential mobility of critical elements in orogenic minerals

In ore geology, metamorphism and associated remobilization processes can impact positively or negatively ore deposits and mineralization (Table 2). Metamorphism(s) and deformation(s) can form favorable traps and enhance ore preservation (i.e., foliation or fold hinges; e.g. Windh 1995; Chauvet 2019; Sayab et al. 2025) but can also erase primary ore texture and chemical signature for understanding ore formation. During metamorphism, ore enrichment may occur through remobilization; however, depending on the metamorphic conditions and tectonic contexts, metamorphism can also have detrimental effects, leading to metal dispersion through remobilization (Tomkins, 2007).

In complex metamorphosed systems, some authors have proposed a detailed multi-scale approach to unravel the geometric effects of primary versus secondary metamorphic features (Lightfoot et al., 2017; Cugerone et al., 2018a; Cugerone et al., 2018b; Cugerone et al., 2023; Paradis et al., 2023; Tian et al., 2024; Sayab et al., 2025). In the 90's several structural geologists examined Pb-Zn ores, highlighting the major structural control on ore genesis (e.g., Aerden 1993, 1994; Cook et al. 1993; Glen 1995).

In these structurally reworked systems, Ge-Ga-In may have been remobilized similarly to what has been found in the Pyrenees, where complex remobilization of stratabound Pb-Zn ores into Ge- and Ga-rich vein deposits has been documented, along with redistribution of Ge and Ga during dynamic recrystallization of sphalerite (Cugerone et al., 2020; Cugerone et al., 2024). Aerden (1993) structural work showed that the

Pb-Zn Hercules deposit in Tasmania was formed by syn-metamorphic remobilization of disseminated primary sulfides in the Mount Read Volcanics into structural traps (folds and shear zones) at supracrustal levels. Similarly, the structural and microtextural work of Perkins (1997) showed that the Pb-Zn ore at Mount Isa in Australia formed by a late syn-deformational replacement of the large-scale Cu orebodies. Cave et al. (2022) proposed that the In-rich Zn-Pb-Ag ore at Mount Novit formed during a major thrusting event along the Mount Isa Fault. In other deposits of the Mount Isa inlier, metamorphic overprint is noticed such as in the Georges Fisher or Hilton deposits (Fig. 7A; Murphy 2004; Cave et al. 2020b). In Greenland, the carbonate hosted Black Angel Pb-Zn deposit has been impacted by intense deformation with Durchbewegung breccia in marble hosted sphalerite ore (Fig. 7B; Horn et al. 2018; Saintilan et al. 2024). Other carbonate hosted deposits show large impact of deformation on pre-existing low temperature (<250 °C) veins, with partly recrystallized sphalerite (Fig. 7C; Cugerone et al. 2020) and folded sphalerite-rich ore bodies (Fig. 7D; Paradis et al. 2023). In the Lachlan orogen, Glen (1995) suggested that the formation of most of the base and precious metal deposits hosted in metasediments might have been controlled by thrusts and are therefore syn-tectonic/epigenetic and not syn-sedimentary/syngenetic as commonly assumed. Understanding ore metamorphism and distinguishing primary structures from metamorphic ones is often challenging due to the frequent transposition of structures in metamorphic terranes (Perkins and Bell, 1998; Cugerone et al., 2018b; Horn et al., 2018).

In Co or PGE rich ores, the Dahenglu Cu-Co ore is a structurally-controlled orogenic-related deposit, with significant enrichment in Co associated with the second foliation (S2; Fig. 7E; Tian et al., 2024). The Thompson deposit in Canada has been described by Lightfoot et al. (2017) to unravel structures associated with magmatic and overprinting metamorphic processes (Fig. 7F). The Ni-Co ore is largely folded and metamorphosed (Fig. 7F), and Ni content varies strongly according to the structural position and the degree of deformation of the ultramafic rocks. Therefore, it is expected that Co and PGE contents may also vary accordingly, but this still needs to be explored. Metamorphic impact (greenschist to amphibolite) on PGE-rich ore has been observed at the Garson mine but shows little impact on the bulk PGE of the rock (Fig. 7G; Sudbury; Mukwakwami et al. 2014a, b). This underscores the challenge of characterizing the scale of CMs mobility– from the nano- and microscale up to the meter scale – and does not rule out redistribution at the micro- to millimeter scale. In the Rajapalot region, orogenic-related Co-rich ores occur mostly in dilated fold hinges (i.e., saddle-reef; Fig. 7H; Sayab et al. 2025).

Examination of ore deformation structures needs to be done at all scales coupled to other in situ geochemical methods (geochronology, isotopy) which could give insightful observations to evaluate and revise better the origin of ore deposits (e.g. Perkins 1997; Cave et al. 2022). As an example, the recent study of Bertauts et al. (2024) shows that Pb-Zn-

**Table 2**

Simplified positive and negative consequences of the impact of metamorphism and deformation on ore.

<table><thead><tr><th colspan="4">Ore Metamorphism</th></tr><tr><th>Beneficial effects on ore</th><th></th><th>Deleterious effects on ore</th><th></th></tr></thead><tbody><tr><td>Structural traps and ore preservation</td><td>← Misleading ore textures that complicate interpretation of primary versus metamorphic features</td><td>→ Destruction of primary ore texture and chemistry</td><td></td></tr><tr><td>Ore enrichment through metamorphic remobilization</td><td></td><td>Metal dispersion through metamorphic remobilization</td><td></td></tr><tr><td>Formation of valuable orogenic (critical) minerals</td><td></td><td>Formation of less valuable minerals (processing not adapted)</td><td></td></tr></tbody></table>
<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

<figure><img src="image_16.png" /></figure>

(caption on next page)
**Fig. 7.** Macroscale example of metamorphosed/recrystallized ore. A. Sulfide-bearing stratabound layers reworked as a foliation in the Hilton deposit (Mount Isa, Australia; modified from Cave et al. 2020b); B. Sphalerite-rich ore crosscutting folded clast of marble and with a Durchbewegung brecciated texture (Black Angel deposit, Greenland; modified from Horn et al. 2018); C. Recrystallized sphalerite-bearing ore with foliation superimposed on sphalerite (Arre, France; modified from Cugerone et al. 2020); D. Sphalerite-rich ore intensely folded in the Reeves MacDonald deposit (Canada; modified from Paradis et al. 2023); E. Folded schist with syn-metamorphic Co-rich pyrite veins parallel to axial plane (Dahenglu deposit, China; modified from Tian et al., 2024); F. Intensely deformed Ni-Co ore in the Thompson mine (Canada; modified from Lightfoot et al. 2017); G. Deformed and foliated Fe-Ni-bearing ore from the Ni-Cu-PGE sulfide ores at Garson Mine, Sudbury (Canada, modified Mukwakwami et al., 2014); H. Cobalt-rich sulfides localized in a fold hinge (saddle-reef style; Rajapalot, Finland; modified from Sayab et al. 2025). Abbreviations: Ccp: chalcopyrite; Dol: dolomite; Pn: pentlandite; Po: pyrrhotite; Sp: sphalerite.

Ag deposits from the Alps show no pre-Alpine inheritance, clearly inferring an orogenic mineralization driven by fluids localizing in Alpine shear zones.

## 4.4. Microscale model for complex metamorphosed ores

### 4.4.1. Mobility and stability of sulfides during metamorphism

The modification of the CMs concentration by metamorphism may occur with two general processes: i) Redistribution (as proposed by Anenburg et al. 2018) occurs when CMs concentrations are not modified at the sample scale and are just subjected to a change in mineral host; ii) Remobilization processes are associated with an open system, generally at larger scale, and controlled by various processes (such as structural pipe and traps). As an initial implication for exploration, if only redistribution occurs, the bulk rock chemistry and ore grade may remain unchanged and may not reveal these processes. However, the primary host of CMs may change, necessitating adjustments to ore processing strategies (Table 2; Fig. 8A). Remobilization or redistribution of CMs might be expressed in different forms due to the competing effects of temperature, deformation, recrystallization, and metamorphic fluids. A general thermodynamics rule proposes that the presence of chemical impurities in the effective bulk composition (for example CMs in rock-forming minerals) expands the Pressure – Temperature stability field of minerals (Yardley and Bodnar, 2014; Yardley and Cleverley, 2014). In that case, temperature would lock CMs into the crystallographic structure of an ore-forming mineral for which the solid solution field expands with increasing temperature. Instead, cooling usually triggers reequilibration of the mineral phases, inducing a large amount of textural (recrystallization, intra-granular deformation) and mineralogical (exsolution, newly formed mineral) changes on the parent mineral/rock. In this case, CMs may be mobilized from parent mineral/rock, if favorable thermodynamic conditions are achieved during metamorphism. These liberated metals may precipitate into newly formed CMs-rich minerals, potentially strengthening and stabilizing the host mineral (Fougerouse et al., 2023) and leaving behind a depleted, recrystallized mineral fraction. In Fig. 8A, two models show potential examples of CMs mobility in orogenic minerals associated with metamorphism and related static and dynamic recrystallization features (modified from Cugerone et al. (2021), inspired by Vokes 1969). These micrometer scale textural features are particularly hard to detect with conventional techniques (microscopy without etching, SEM), especially in sulfides.

Experimental and natural observations on sulfides (e.g., sphalerite, chalcopyrite, pyrrhotite, galena, pyrite) potentially rich in CMs have demonstrated ductile behavior at low temperatures (as low as 100–200 °C at 0,5 kbars; Fig. 8B), especially for the very ductile sulfides like sphalerite, galena, chalcopyrite, pyrrhotite (Clark and Kelly, 1973; Kelly and Clark, 1975; Marshall and Gilligan, 1987; McQueen, 1987; Siemes et al., 1991; Barrie et al., 2011). Pyrite is relatively stronger than this group of very ductile sulfides even if Barrie et al. (2011) showed occurrence of dislocation creep mechanism as low as 260 °C. More experimental data are needed on metamorphosed sulfides correlated to CMs rich systems to precisely evaluate the conditions needed for CMs remobilization, which may affect CMs hosted within the crystallographic lattice of primary ore.

### 4.4.2. Analytical techniques: integrating textural and chemical mapping data

Conventional microscopic and chemical investigations often lack the spatial precision needed to understand these complex sulfide systems overprinted by metamorphism, which may exhibit multiple deformation textures. In sulfide mineralogy, the use of advanced textural techniques such as electron backscattered diffraction (EBSD) mapping is particularly useful to detect grain boundaries (not observable in most sulfide minerals under classical reflected light microscopy; Boyle et al. 1998; Prior et al. 1999). Basic microscopic views of pyrite, chalcopyrite, tenantite, and sphalerite are compared with EBSD maps of the same regions in Fig. 9, highlighting the significant limitations of relying solely on microscopic observations for accurate information on sulfide texture. This technique also provides detailed information about intragranular features, such as twin shapes and misorientation patterns, which are essential for understanding the conditions of sulfide (de)formation (Barrie et al., 2010; Vukmanovic et al., 2014; Fougerouse et al., 2019). Although combining EBSD with chemical mapping remains time-consuming and is often not prioritized in understanding ore deposit formation, it should be applied to all orogenic-related deposits, at least on several representative samples, to avoid potential misinterpretations on relationship between metamorphism and mineralization event, and to improve our general understanding of these complex metamorphosed mineral textures.

At thin section scale, chemical mapping of CMs systems in orogenic domains is essential for detecting potential diffusion or dissolution mechanisms, correlation between elements and identifying mineral inclusions. These data may help understanding the formation of orogenic minerals rich in CMs and may guide exploration in specific mineral structures or textures. In metamorphosed domains which are frequently thermodynamically metastable, many studies show the presence of inclusions of all sizes, from nanometer to millimeter scales (Cook et al., 2009; Fougerouse et al., 2023). Then, scale of measurements is critical before interpreting trace element incorporation in mineral (Reddy and Hough, 2013; Reddy et al., 2020; Fougerouse et al., 2023). Investigation with scanning electron microscopy (SEM) may constrain the distribution of nano to micro inclusions. Advanced tools such as transmission electron microscopy (TEM) or Atom probe tomography (APT) can identify nanoscale inclusions and the analysis of potential chemical gradients around them, providing valuable insights into the precise natural processes involved in the formation of orogenic minerals rich in CMs (Reddy and Hough, 2013). However, the primary weakness in economic geology of this kind of tools, arises from the actual time-intensive processes of sample preparation and data analysis, which typically limit the selection to only a few representative samples for TEM and APT studies.

Given the large numbers of CMs and their thermo-chemical properties, the specific thermodynamic and metamorphic conditions leading to transport and deposition of specific orogenic minerals rich in CMs may vary from one to the other. A quantitative assessment of the economic weight of orogenic minerals rich in CMs for each type of deposit is beyond the scope of this article and is also too early considering the recent interest for orogenic minerals. However, in the following section and based on a literature review, a series of examples for the two major chemical systems selected will be presented and discussed.
<figure><img src="image_17.png" /><figcaption>**Fig. 8.** A. Sample-scale model for the remobilization and concentration of critical elements associated with static (left) or dynamic (right) metamorphic recrystallization. Upon metamorphism and deformation, primary stratabound or vein type ore may be subjected to static or dynamic recrystallization: critical elements are expelled from the host mineral lattice and recrystallized in newly formed accessory minerals enriched in critical elements, leaving behind a depleted recrystallized matrix of parent host mineral; B. Brittle-ductile transition in several sulfide minerals as a function of temperature and pressure (experimental data; modified from Marshall and Gilligan 1987 and references herein). Classic metamorphic gradients (20, 35, 60 °C/km) are represented. Note that more recent work on pyrite showed lower brittle-ductile transition as low as 260 °C (Barrie et al., 2011). Abbreviations: Ccp: chalcopyrite; Gn: galena; Po: pyrrhotite; Py: pyrite; Sp: sphalerite.</figcaption></figure>
Conventional petrography

<figure><img src="image_18.png" /></figure>

EBSD

<figure><img src="image_19.png" /></figure>

**Fig. 9.** Comparison between conventional petrography (SEM, reflected light microscopy) and Electron backscattered (EBSD) maps of four types of sulfides potentially hosting critical elements. In every cases, grain boundaries are difficult to detect with conventional petrography. A. SEM and EBSD maps (orientation contrast) of pyrite in the Witwatersrand (modified from Reddy and Hough 2013); B. Reflected light microphotograph and EBSD map (band contrast with misorientation boundaries) of chalcopyrite (modified from King et al. 2024); C. Reflected light microphotograph showing pyrite and tennantite and EBSD Euler map (all angle) only on tennantite (modified from Barrie et al. 2007); D. Reflected light scan of sphalerite and galena and EBSD grain size map focused on sphalerite (modified from Cugerone et al. 2024).
**5. Key examples of orogenic minerals rich in critical elements from different chemical systems**

These examples are by no means exhaustive but highlight several metamorphic processes leading to the mobility of CMs in orogenic minerals whether they are simply redistributed or upgraded in the ore or released from the system. Based on their frequency and their economic importance, their occurrences and exploration have to be reconsidered.

**5.1. Metamorphosed deposits with orogenic minerals rich in gallium, indium and germanium**

In metamorphosed Pb-Zn deposits, several authors (Lockington et al., 2014; George et al., 2016; Horn et al., 2018) have reported large variations of trace element contents (like Ga, In and Ge) in sulfides, such as sphalerite, chalcopyrite or pyrite, implying that CMs can be upgraded or released from the primary system during secondary metamorphic

processes. At regional scale, ore body thickening following orogenic deformation at amphibolite facies conditions, has resulted in Pb-Zn remobilization and ore upgrading. In addition, prograde partial melting of sulfide at these temperatures allows the formation of melts that may remobilize Pb, Zn and the associated CMs (Tomkins, 2007). At microscale, the role of metamorphism and dynamic recrystallization in triggering the formation of accessory minerals such as Ge-oxides and sulfides has been highlighted for Pb-Zn deposit metamorphosed under greenschist facies conditions of the Pyrenean Axial Zone (Cugerone et al., 2018a; Cugerone et al., 2021). Depending on the respective fugacity of O₂ and S₂ in the associated fluid, either Ge-oxides or Ge-sulfides can be stable (Sahlström et al., 2017). Similarly, Jonsson et al. (2013) have shown that recrystallization associated to regional metamorphism in the Paleoproterozoic Bergslagen Pb-Zn ore province allowed the formation of roquesite (CuInS₂) and controls in variability in this Pb-Zn ore. Roquesite can be a product of metamorphic reaction involving sphalerite and bornite at amphibolite-facies conditions of

<figure><img src="image_20.png" /><figcaption>**Fig. 10.** Microscale observation of typical recrystallized Pb-Zn ore. In each of these deposits, distribution of critical elements such as Ge, Ga, In is certainly largely impacted by recrystallization, fluid circulation and may be distributed in discrete phases (orogenic minerals). A. Deformed sphalerite (Sp) and galena (Gn) with small amount of pyrite (Py) in the giant Mengxing Pb-Zn deposit (China; photo from Ye et al., 2011); B. Highly deformed sulfide assemblages from the Caixiashan Pb-Zn deposit (China; photo from Gao et al., 2020); C. Two sphalerite types probably differently impacted by recrystallization (parent Sp-I and daughter Sp-II) associated with recrystallized galena (Gn) and euhedral pyrite (Py) (Neves Corvo; photo from Carvalho et al., 2018); D. Localized deformation in shear band mostly constituted of sphalerite (Sp), pyrite (Py) and galena (Gn); E-F. Dynamic and static recrystallization of sphalerite in George Fisher and Silverspur, respectively (Mt Isa inlier, Australia; modified from Murphy 2004; etched with concentrated HI).</figcaption></figure>
oxidized copper-rich volcanic- hydrothermal polymetallic systems (Jonsson et al., 2013). These studies rarely consider the spatial scale of the chemical analyses (frequently > 100 µm) to determine the exact host for CMs, which results in the lack of observation of potential orogenic minerals rich in CMs (Fougerouse et al., 2023).

Given that many Pb-Zn deposits are located in ancient orogens, revisiting mines, their waste and tailings may lead to the discovery of novel CMs resources potentially in orogenic minerals. However, exploration for orogenic minerals rich in CMs and the study of deformation-related textures in these settings are often overlooked, despite evidence of metamorphism in some deposits. Textures of deformed ores (that may contain orogenic minerals rich in CMs) with clear zones of sulfide recrystallization parallel to regional foliation (Fig. 8), can be well recognized macroscopically in the field. However, only few examples with detailed textural description exist in the literature, such as some Chinese (Gao et al. 2020; Jia et al. 2023; Fig. 10A and 10B), or European Pb-Zn deposits (Carvalho et al. 2018; Tiu et al. 2021; Cugerone et al. 2024; Fig. 10C and D). In Australia, the Mount Isa Cu-Zn-Pb-Ag deposit in Queensland is a large Proterozoic sedimentary-hosted deposit, located in the Mt Isa Inlier (Valenta, 1989; Perkins, 1996; Perkins, 1997; Cave et al., 2020a). It has been metamorphosed under low-grade metamorphic conditions (<450 °C, <5 kbar) during the Mesoproterozoic orogeny of the Mt Isa superbasin. Large et al. (2005) indicated that sulfide – galena and sphalerite – have recrystallized and a large chemical and textural variability between dynamic and static recrystallization has been reported in sphalerite at the George Fisher Mine as shown in Fig. 10E and F (Murphy, 2004; George et al., 2016). The nearby Hilton deposit shows intense remobilization with a late stage rich in Ge and Ga, with highly zoned sphalerite at microscale (Cave et al., 2020a).

In order to evaluate, as a first assumption, the role of temperature on the occurrence of orogenic minerals rich in CMs, we have reported orogenic minerals clearly identified in the literature (n = 8) for terranes metamorphosed at low- or high-grade conditions (Fig. 12). In Zn and Cu-

rich ores, the occurrence of Ge-rich orogenic minerals appears to be limited to low-grade metamorphic terranes (<450 °C) whereas In-rich orogenic minerals may occur at higher grade conditions (>450 °C).

## 5.2. Metamorphosed deposits with orogenic minerals rich in cobalt and platinum-group elements

Major deposits of PGEs worldwide are located in layered mafic–ultramafic intrusions in intracontinental settings (Schulz et al., 2014; Horn et al., 2021) and the metal content may be redistributed at mineral scale during subsequent secondary metamorphic processes (Mukwakwami et al., 2014b; González-Jiménez et al., 2016). Several deposits show a clear foliation associated with a tectonic reworking of the ore that can be macroscopically recognized in the field (Fig. 7E-H). A recent study on the ultramafic–mafic Paleoproterozoic Panton intrusion in Australia (Beinlich et al., 2020) highlights that PGEs are remobilized and controlled by the thermodynamic stability of PGE-bearing minerals. These preferentially formed within the Main Chromitite Layer that has been metamorphosed, producing a recrystallized matrix of serpentine-chlorite (Fig. 11A-B) during a regional amphibolite facies metamorphic event. In Precambrian layered Ni-Cu-bearing mafic–ultramafic intrusions of the East Kimberley, the mineralized levels showing higher concentrations of Co– and PGE- bearing sulfides are located in the chromitite layers that are most strongly foliated and folded close to the contact with migmatitic/granulitic host rocks (Hoatson, 2000). The juxtaposition between the mafic–ultramafic complex and the sedimentary host rocks is early in the terrane history (ca. 1855 – 1830 Ma). These neighbouring sediments were metamorphosed at high grade during Paleoproterozoic and/or Panafrican orogenesis, and the mafic–ultramafic complex must have undergone regional metamorphism too. This might suggest a reworking and potential upgrading of the original magmatic ore through metamorphic recrystallization as Hoatson (2000) suggests that serpentinization of ultramafic rocks

<figure><img src="image_21.png" /><figcaption>**Fig. 11.** Microscale observation of typical recrystallized Co(–PGE) ore. A. Pd-free Pt-arsenide at the grain boundary between chromite and chlorite and in contact with pentlandite and pyrrhotite (Panton intrusion, Western Australia, Beinlich et al., 2020). B. Pt-free Pd-telluride containing Rh, Ru, and Bi, at a chlorite–serpentine grain boundary (Panton intrusion, Western Australia, Beinlich et al., 2020). C. Cobalt-rich pyrite and siegenite vein parallel to S₁ foliation (Dahenglu, China; Tian et al., 2024). D. Reflected light optical microscope photograph of cobaltite and cobalt pentlandite inclusions in pyrrhotite. These are located within elongated patches concordant with the regional foliation which is marked by chlorite-biotite-sericite schists (Juomasuo Au-Co deposit, Finland, modified from Vasilopoulos et al., 2021).</figcaption></figure>
<figure><img src="image_22.png" /><figcaption>**Fig. 12.** A. Synthesis presenting selected examples of orogenic mineral occurrences enriched in critical metals and metalloids (CMs). The conditions of primary ore emplacement and subsequent metamorphic overprinting are documented; 1-(Murphy, 2004; Cave et al., 2020b); 2-(Horn et al., 2018); 3-(Cugerone et al., 2020; Cugerone et al., 2021); 4-(Reiser et al., 2011); 5(Moura, 2008; Carvalho et al., 2018); 6-(Jonsson et al., 2013); 7-(Zhao et al., 2021); 8-(Werner et al., 2017); 9-(Qiu et al., 2021); 10-(Pan and Therens, 2000); 11-(Saintilan et al., 2017); 12-(Vasilopoulos et al., 2021); 13-(Hoatson et al., 2006); 14-(Beinlich et al., 2020; Le Vaillant et al., 2020); 15-(Mota-e-Silva et al., 2015); 16-(González-Jiménez et al., 2016); Abbreviations: Ccp: chalcopyrite; Chr: chromite; Pn: pentlandite; Po: pyrrhotite; Sp: sphalerite; B. Basic example of a P-T paths of a Ge-rich sphalerite metamorphosed following a geothermal gradient of 30 °C/km, from the study of Cugerone et al. (2024) (more information on the diagram in the Fig. 8B). At high P-T (amphibolite grade), Ge-minerals (newly formed oxides, spinels) are probably dispersed and not stable. Greenschist conditions are certainly the upper limit for the preservation of these minerals rich in Ge. Following the study of Marshall and Gilligan (1987), sphalerite would be ductile at temperatures at low as 70–80 °C and 0.5 kbars in a geothermal gradient of 30 °C/km.</figcaption></figure>

through metamorphism and deformation is an efficient process to concentrate PGEs but the detailed thermodynamic conditions still need to be determined. As a further example, in the massive sulfide ore of Limoeiro Ni-Cu-PGE deposits in Brazil that was metamorphosed during the Pan-African orogeny (Mota-e-Silva et al., 2015), PGEs may have been redistributed by high-grade metamorphic processes that have controlled the metamorphic crystallization of merenskyite (PdTe₂). González-Jiménez et al. (2016) have clearly stated that the formation of PGE-minerals during retrograde metamorphism may be generally overlooked and that these are also likely to form under greenschist to amphibolite facies (not only at magmatic temperatures). The Dahenglu deposit in China is hosted in Paleoproterozoic rocks and shows syn-metamorphic Au-Co-rich veins rich in pyrite and siegenite (Fig. 11C), highlighting the role of metamorphism and structural control on the

formation of Co-rich veins in Precambrian rocks (Tian et al., 2024).

In Europe, most Co deposits are hosted in the Fennoscandian Shield that has endured several intracontinental rifting events and orogenies (Horn et al., 2021). These are classified mostly as magmatic, metasedimentary hosted or associated with Au in orogenic-style veins (Lahtinen et al., 2022; Sayab et al., 2025). However, in Finland, the Juomasuo volcano-sedimentary deposit shows textural relationships indicating that Co-minerals are mostly located within greenschist facies rocks (Fig. 11D) and that the Co-rich ore emplacement was triggered by the presence of a reduced metamorphic fluid (Vasilopoulos et al., 2021). Local enrichment in Co is also found in cobaltite and linnaeite from the Rajapalot deposit strongly associated with regional metamorphism (Sayab et al., 2025).

Occurrences of orogenic minerals rich in Co and PGE cannot be
further constrained by the temperature that influenced the primary deposit because these orogenic minerals occur in terranes that underwent a large range of temperature reworking with frequent polymorphic overprint (Fig. 12).

## 6. Conclusions

- Metamorphism of primary ore can either enhance or hinder the exploration and processing of base and critical metals/metalloids (CMs);

- In most studies, the effect of metamorphic overprint on ore is likely underestimated because suitable and efficient methods to map the spatial distribution of CMs in complex sulfide mineralization are lacking;

- Orogenic minerals form as a result of orogenic processes such as deformation, recrystallization, and the influence of metamorphic fluids; During metamorphism, Ge and In are mobile, with Ge-rich orogenic minerals essentially formed at greenschist conditions (< 450 °C). Indium-rich orogenic minerals can be mobilized at higher temperatures (> 450 °C).

- Cobalt and PGE-rich ores are frequently hosted in ancient terranes and may have endured superimposed (poly-)metamorphism. The formation of orogenic minerals rich in Co and PGE are described in high temperatures (> 450 °C) metamorphosed sulfides; however, the behaviors of Co and PGE in metamorphic domains remain poorly constrained because of the absence of multiscale analyses and the inherent complexity of these frequent polymorphic systems hosted in Precambrian rocks.

- Techniques linking chemical and microstructural information at thin section scale need to be widely applied on metamorphosed sulfides to better understand the textural changes of sulfides at various metamorphic grades and to better constrain the conditions under which critical metals become mobilized, and the sulfides deformed.

- The spatial resolution needs to be systematically evaluated for any chemical analyses in metamorphic domains. The frequent presence of nano- to micro-scale inclusions can significantly influence the geochemical signals (elemental composition, isotopy) in sulfides, potentially leading to numerous pitfalls in data interpretation.

## Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Benedicte Cenki reports financial support was provided by French National Research Agency. Benedicte Cenki reports a relationship with University of Montpellier that includes: employment. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

BC acknowledges the support of the Agence Nationale de la Recherche, France (ANR), under grant ANR-23-CE01-0017 (project CMiO). The authors gratefully acknowledge K. Goodenough for her constructive comments on a previous version of the article. We thank two anonymous reviewers for constructive comments on our article and Huayong Chen for editorial handling. AC acknowledges J. Mercadier and C. Ballouard for fruitful discussions on the topic. M. Alsaif and N. Meynard are warmly thanked for proofreading an earlier version of the manuscript and the supplementary table, respectively. We also would like to thank T. Murphy, A. Beinlich, M. Vasilopoulos, B. Cave and J. Mukwakwami for sharing their original figures. Finally, BC has started maturing the idea for this article since October 2019, following an invited talk at Adelaide University entitled "Critical Minerals Geosciences - research directions and future opportunities" and she is

deeply thankful for the colleagues who have invited her at that time.

## Appendix A. Supplementary material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.oregeorev.2025.106904.

## Data availability

Data will be made available on request.

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