# First isotopic characterization of the planet neolithic Pb-Cu reduction workshop (Fayet/Cénomes mining district, aveyron, france)

K. Costa, Céline Tomczyk, Gilberto Artioli, C. Canovaro, C. Chauvel, Pamela

Gutiérrez, Michel Maillé

► To cite this version:

K. Costa, Céline Tomczyk, Gilberto Artioli, C. Canovaro, C. Chauvel, et al. First isotope characterization of the planet neolithic Pb-Cu reduction workshop (Fayet/Cénomes mining district, aveyron, france). Journal of Archaeological Science: Reports, 2025, 66, pp.105314. 10.1016/j.jasrep.2025.105314. hal-05321634

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Submitted on 31 Oct 2025

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# First isotopic characterization of the planet neolithic Pb-Cu reduction workshop (Fayet/Cénomes mining district, aveyron, france)

K. Costa<sup>a, *, D</sup>, C. Tomczyk<sup>a</sup>, G. Artioli<sup>b, D</sup>, C. Canovaro<sup>b, D</sup>, C. Chauvel<sup>c</sup>, P. Gutiérrez<sup>c</sup>, M. Maillé<sup>d</sup>

## ARTICLE INFO

Keywords:

Copper

Lead

Isotopes

Neolithic

Metallurgical workshop

## ABSTRACT

Excavations at the Planet site have uncovered a substantial multi-stratified complex dedicated to copper and lead metallurgy, including several workshops that operated between 2850 and 2480 BCE. Situated in the southern Massif Central, near deposits rich in copper, lead, antimony, and silver, the site marks a significant development in early copper and lead metallurgy by late Neolithic communities. This article aims to enhance archaeological and mineralogical analyses of the metallurgical process by providing a first isotopic characterization of excavated materials, specifically key elements in the production chain: ores, slags, and metal. Additionally, we present an initial isotopic comparison of lead with samples from nearby deposits. This study deepens our understanding of the site's local resource sourcing while establishing a preliminary reference framework for comparing analyses of contemporaneous artifacts from the region.

## 1. Introduction

The Planet metallurgical site was discovered in 2014 following the unearthing of a statue-menhir with abstract designs during agricultural work. This discovery raised several questions regarding the megalith's context, including its location, layout, and possible domestic or specialized functions, leading to the initiation of planned archaeological excavations (Maillé et al., 2021, Maillé et al. (2019)). Although these excavations did not fully resolve the original inquiries, they revealed an unexpected site dedicated to metallurgical production. Consequently, further research and studies focused on these activities were undertaken.

The Planet site is located approximately 18 km from the Larzac and Avant-Causses limestone plateau, areas rich in Neolithic remains (Costantini, 1984). Notable finds in these regions include dolmens containing copper and lead artifacts (Arnal et al., 1979; Guilaine and Vaquer, 1976). To the west, the expansive Rougier de Camarès depression has yielded numerous statue-menhirs and evidence of Neolithic settlements (Maillé, 2010).

In this cultural landscape, which thrived between 3500 and 2200 BCE, a significant quantity of copper-based ornaments, awls, and

daggers have been documented. This region, marked by a strong presence of statue-menhirs and metallurgical activities, is associated with the Treilles cultural group, known for its abundant metal artifacts (Costantini, 1984). The samples selected for this study come from the Planet site, situated within this cultural context. The site includes both domestic areas and zones of extensive metallurgical activity, evidenced by the presence of numerous production remnants such as ores, slag, metal, and ore reduction furnaces. Based on current excavation findings, which remain ongoing, all metallurgical activities have been dated by carbon-14 dating and archaeomagnetic analysis to the Final Neolithic or Chalcolithic periods, specifically between 2850 and 2480 BCE. However, excavations of archaeological layers dated to 3300 BCE have not yet yielded sufficient evidence to confirm metallurgical activity during that earlier period. The incipient metallurgy at Planet seems to be roughly coeval to the beginning of exploitation of copper in the Eastern Alpine region (Artioli et al., 2024).

Prior to the discovery of these workshops, copper metallurgy was the predominant form of metal production during these periods in southern France and, more broadly, in western Europe. Although gold metallurgy was occasionally present, it remained limited due to scarce resources,

<footnote><sup>a</sup> UMR 7041 Archéologie Et Sciences De l'Antiquité (ArScAn), Université Paris 1 Panthéon Sorbonne, Paris, France</footnote>

<footnote><sup>b</sup> Centro CIRCe e Dipartimento di Geoscienze, Università di Padova 35131 Padova, Italy</footnote>

<footnote><sup>c</sup> Université Paris Cité, Institut de physique du globe de Paris, CNRS, F-75005 Paris, France</footnote>

<footnote><sup>d</sup> UMR 5608 TRACES, CNRS, Université Toulouse Jean Jaurès, 5 Allée Antonio Machado, 31058 Toulouse, France</footnote>

<footnote>* Corresponding author at: 15Bd Lascrosses, Bat. D1, 31000 Toulouse, France.</footnote>

<footnote>E-mail address: contact.kevin.costa@gmail.com (K. Costa).</footnote>
and other metals such as lead were regionally attested by jewellery, but the number of artefacts recovered from archaeological contexts is very limited (Rovira and Strahm, 2019). The Planet site shows evidence of local metallurgical activity, particularly involving the processing of locally abundant tetrahedrite and bournonite. These minerals, found in a crushed form (approximately 3 cm in size) in some waste dumps. They could correspond to rejected ores, but they also are indicative of smelting activities at the site (we will test this hypothesis in this study). Smelting activity is supported by the discovery of well-preserved reduction structures, porous ochre slag from smelting, metal ingots, and metallurgical tools (Fig. 1).

What distinguishes the Planet site from other known metallurgical sites in western Europe is a high proportion of lead, both in the slag and in the bournonite-type ores. The discovery of several lead-based ingots and amorphous metallic objects confirms the production of lead on-site (Costa et al., 2021; Maillé and Costa, 2021). In contrast, while copper extraction and refining structures are commonly found in Chalcolithic contexts, the Planet site complements other significant discoveries such as Al Claus in Tarn-et-Garonne (Carozza et al., 1997), Les Clausis in Saint-Véran, Hautes-Alpes (Barge et al., 1997), and the Cabrières-Péret complex in Hérault (Ambert, 1995; Espérou, 2008).

The substantial regional and supra-regional metallurgical activity evident at these sites raises important questions about the circulation of ores smelted at the Planet site and the final composition of the metal compounds produced there, such as leaded copper, copper with antimony and silver, lead, and lead-copper alloys. Analysis not only of the slag but also of all steps of the Chaîne Opératoire, from ore to metal, indicates that copper, lead, and pseudo-alloys combining these two metals were produced here. The Planet site thus served as a significant regional center for the production of copper and lead between 2850 and 2480 BCE.

The abundance of metal objects found at nearby sites, dated to the same period, led us to investigate the role of this workshop within local and regional cultures. To this end, we aim to characterize not only the production at the Planet site but also the surrounding metal deposits, in order to develop an initial isotopic reference framework for comparison with contemporary local artifacts. The elemental compositions of many artifacts from this area are characterized by high levels of antimony, silver, and lead, and low levels of arsenic and nickel, a distinct chemical profile typical of the region (Costa, 2023; Espérou, 2008; Junghans et al., 1968). These compositions suggest they could have been produced using the tetrahedrite(–tennantite) mineralization found in local deposits. To confirm this hypothesis, it is essential to obtain the lead isotopic signatures of both local copper and lead ores and, crucially, those of the artifacts produced at the Planet site. This article begins with a contextualization of the site, followed by a detailed presentation of the isotopic approach employed in this research.

## 1.1. Geological context

The Planet site is situated at an altitude of 465 m in the mid-mountainous region of the Southern Massif Central (France), in the Aveyron department into Fayet District (Fig. 2). Located only 65 km from the Mediterranean, this area is drained by the Orb River to the east and the Dourdou and Sorgue, tributaries of the Tarn River, to the west. Approximately 50 km Southeast lies the Cabrières-Péret mining complex, which was exploited during the same period for its antimony-rich copper deposits (Ambert, 1995; Ambert et al., 2005, 1998; Bourgarit and Mille, 2005; Espérou, 2008).

The Planet site is set in a geologically complex zone on the north-eastern slope of the Montagne Noire's axial zone, where numerous metalliferous deposits, notably of copper and lead, have been documented (Leblanc, 1997; Milesi, 1982). Most of these deposits occur at the top of Lower Cambrian limestones in contact with schists and exhibit hydrothermal mineralization, including baryte, quartz, copper carbonates (azurite and malachite), silver-bearing galena, sphalerite, and

chalcopyrite. Additionally, many of these deposits contain tetrahedrite ($Cu_{12}Sb_4S_{13}$) and bournonite ($PbCuSbS_3$), along with secondary alteration minerals such as malachite, azurite, and bindheimite (Guérangé-Lozes and Guérangé, 1991). The exploitation of these mineral resources in the Late Neolithic period has been confirmed by the discovery of mining remains from that era into Fayet/Cénomes mining district, including the Bouche Payrol and La Fage mines (Barge, 1985; Houlès, 1994; Lechelon, 1997) and, more recently, the La Baumé mine, also known as "Le Puits-aux-Romains" (Léchelon, 2011; Maillé, 2018).

The closest copper deposit is the Lacan orebody, along with the Cénomes District (Fig. 3). These deposits are distributed along fault lines at the interface of two Cambrian geological horizons (k2/k3), with the exception of the Ceilhes District, which is also associated with the plutonic basement. A mining area located 40 km further north, where numerous archaeological sites and dolmens have yielded significant amounts of copper objects, has also been subject to initial investigations, particularly at the Verrières mine (hosted in Sinemurian and Hettangian dolomites).

However, isotopic data remain scarce for the mining area encompassing the Fayet/Cénomes District. The initial focus on copper metallurgy had to be broadened to include regional lead deposits, due to the identification of Neolithic lead metallurgy. Lead-bearing mineralizations and ore deposits in the Massif Central have been the subject of numerous studies regarding their formation processes, which led to both geological and isotopic analyses of these deposits (Marcoux, 1986). The Malines mine, in particular, has been extensively documented and studied (Guen et al., 1991) in relation to the same mineral identified at the Planet site: bournonite. This specific lead-rich mineral is widespread in local deposits, and we sought to determine whether other ore bodies containing these polymetallic sulfides could be differentiated isotopically. This also allows us to compare our new analyses to previously established datasets. To assess the possibility of distinguishing the Planet workshop and the Fayet/Cénomes mining district from other regional datasets, we also chose to analyze several more distant deposits, including some located within the Southern Paleozoic Fold and Thrust Belt in the Cévennes region. Similarly, we included the Verrière deposit, situated within the Upper Gneiss Unit, as well as the Sainte-Lucie deposit in the Margeride area, within the Mont-Lozère zone (Fig. 2).

## 1.2. Why lead isotope Analyses?

Lead isotope analysis of copper and lead in archaeological artifacts is valuable because of the consistent presence of lead in both lead and copper mineralization (in trace amounts on the order of parts per billion). Lead has four isotopes, three of which ($^{206}\text{Pb}$, $^{207}\text{Pb}$, and $^{208}\text{Pb}$) are radiogenic, produced by the radioactive decay of uranium (U) and thorium (Th), while one isotope, $^{204}\text{Pb}$, is primitive and stable. Expressed as ratios, lead isotopes provide a unique signature depending primarily on the age of formation, and they can be used to characterize specific deposits (Cannon et al., 1961; Faure and Mensing, 2013).

This isotopic signature remains stable through metallurgical processes (Cui and Wu, 2011; Pernicka, 2014), allowing for reliable comparisons between artifacts and ore sources. Isotopes are not fractionated by reduction processes; however, conducting analyses directly at production sites—where mixtures of ores and metals from different sources may occur—provides a more robust framework for evaluating the relevance of sourcing finished objects by directly comparing archaeological and geological data. By analyzing the lead isotopic ratios of both the Planet site productions and the surrounding ore deposits, we can trace the origin of metal objects, thereby enhancing our understanding of resource circulation and the metallurgical practices of the period.

# 2. Sampling and analysis methods

Micro-sampling was conducted using a micro-drill equipped with diamond bits, particularly for ore samples. Sample sizes varied
<figure><img src="image_4.png" /><figcaption>Fig. 1. Overview of the metallurgical chaîne opératoire at the Planet site.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Massif central geological context with deposits and Planet archaeological site sampling in this study (map background: Faure et al., 2009). 1: Fayet/Cenomes District; 2: Verrières ore deposit; 3: Ceilhes ore deposit; 4: Cévennes district; 5: Mont Lozère deposits; 6: Rieucros ore deposit.</figcaption></figure>

depending on the ore type and lead concentration, with quantities ranging from 3 to 10 mg. The same approach was applied for slag samples. The samples were analysed beforehand to determine their mineral and chemical nature (Costa et al., 2021; Costa and Maillé, 2022).

## 2.1. Mineralogic and compositional analysis

### 2.1.1. SEM

The ores and slags analyzed were cut, embedded in resin, then

polished and examined using a scanning electron microscope as part of a previous study (Costa et al., 2021). The mineral phases identified in the ores were subsequently micro-sampled, as previously described. The same protocol was applied to the slags.

#### 2.1.2. pXRF

pXRF analyses are semi-quantitative surface analyses. In the context of this study, we used this technique to identify the metal composition of the ingot discovered on the archaeological site. The pXRF device used was a Tracers 5i from Bruker. The ingot was analyzed using an alloy
<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Location and geological context of the Planet archaeological site into Fayet/Cenomes mining District (BRGM geological map). Several mining districts are indicated: (1) Bouco Payrol District: Includes four mines—Bouco Payrol 1, 2, 3, and 4. (2) Fayet/Sylvanès District: Includes mines such as Puech de Roste, La Baume, and Le Puits aux Romains. (3) Brusque District: Includes mines such as Cribas and Brusque. (4) Cénomes District: Includes mines such as La Cave, Puits du Réservoir, Ruisseau du Pourtel, La Fage, and Mourgis. (5) Ceilhes/Avène District: Includes mines such as Bournac, Mange-Hommes, Lastours, Col du Brunal, Mont Faulat, Fontaine des Allemands, Les Maynes, La Rabasse, Corbières, and Col de la Moutoune. (6) Lacan ore deposit.</figcaption></figure>

calibration directly on its surface due to restrictions related to administrative sampling permissions. Based on the results of this semi-quantitative analysis (Costa and Maillé, 2022), we subsequently obtained permission to sample the area with the highest lead concentration.

## 2.2. Lead isotopic analysis

### 2.2.1. Analytical protocol

The precise discrimination of the individual lead isotopes and their simultaneous detection is critical for accurate measurement using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS).
Sample preparation was carried out following established protocols at the University of Padua (Villa, 2009) and the Institut de Physique du Globe de Paris (IPGP) (Chauvel et al., 2011).

At the University of Padua, a few milligrams of metal were dissolved in highly concentrated, triple-distilled nitric acid within PTFE (Teflon) vials. Lead was then separated using SrSpec resin (El ChroM Industries) in PTFE columns and eluted with 3 ml of 0.01 M HNO₃.

At IPGP, mineralization was carried out with a nitric acid and oxygenated water mixture. After evaporation, samples were dissolved in 0.7 N HBr and processed through retractable Teflon columns filled with AG1-X8 resin. The matrix was removed using 0.7 M HBr and 2 M HCl, and lead was subsequently eluted with 6 M HCl. To ensure the highest purity, the chromatography process was repeated twice, yielding the purest possible fraction of lead for isotopic analysis.

### 2.2.2. Multi-Collector mass spectrometer analysis (MC-ICP-MS)

Lead isotopic ratios $^{206}$Pb/$^{204}$Pb, $^{207}$Pb/$^{204}$Pb and $^{208}$Pb/$^{204}$Pb were measured at the Institut de Physique du Globe de Paris (IPGP) using a Thermo Scientific Neptune multi-collector mass spectrometer (MC-ICP-MS). The dried samples were first dissolved in 7 N nitric acid. To ensure consistent concentrations across all samples for MC-ICP-MS measurement, an aliquot equivalent to 5 % of the sample was analyzed to verify chemical recoveries. Additionally, a Thallium (Tl) internal standard was added to all samples to correct for mass bias internally (White et al., 2000).

To assess data quality, a procedural blank (measured at 280 pg total solution) and one duplicate sample were measured. External normalization was applied via sample-standard bracketing using the NIST SRM 981 standard, based on reference values from (Jochum et al., 2011).

## 3. Materials analyzed

The samples selected for this study originate from the Planet site. They correspond to several occupational phases identified during excavation, though their precise duration remains undetermined due to limitations in current radiocarbon (C14) dating methods. These 22 phases, identified through stratigraphic analysis, are numbered from 1 (most recent) to 22 (oldest). These phases are all dated between 2890 and 2480 BCE; however, due to a radiocarbon plateau, it is currently not possible to date each of them more precisely. Additionally, as part of a collective research program titled "Mines et métallurgie pré/protohistoriques en région Occitanie" ("Pre/Protohistoric Mines and Metal-lurgy in the Occitan Region"), copper deposits in the region were investigated. Several mines with diachronic exploitation have been documented, with some evidence of activity as early as prehistoric times. Although these sites indicate potential copper exploitation dating back to the Chalcolithic period, no isotopic reference dataset has been established for these deposits. This study facilitates the isotopic characterization of the production site, allowing for a comparative analysis with nearby raw material sources (Fig. 4).

The initial selection of materials for analysis included various elements from the Chaîne Opératoire, spanning multiple chronological phases. The objective was to determine the consistency or variability of sources and products. After sampling, the ores and slag underwent scanning electron microscopy (SEM) analysis, enabling detailed mineralogical characterization of materials processed at the site and isotopic analysis. Lead concentrations were determined by SEM and XRF analyses (Costa et al., 2021); this previous study now enables the isotopic analysis of the same materials.

### 3.1. Ores

Four types of ore were analyzed from the Planet site: tetrahedrite, bournonite, malachite, and bindheimite. Each mineral provides insight into the materials used and processed in the workshop across its occupational phases. Mineralogy was determined using SEM in order to

identify the copper and lead contents and the specific mineral phase sampled for isotopic analysis.

Tetrahedrite: This copper-based sulfide, containing variable amounts of antimony, silver, iron, zinc, and arsenic, has the general formula (Cu, Fe, Zn, Ag)₂(Sb, As)₄S₁₃. It belongs to the gray-copper mineral family, with a copper content of approximately 40–50 %. Known to have been mined in the Chalcolithic period in the Cabrières-Péret region of Hérault, the tetrahedrite sample analyzed here dates to the early occupational phase of the site (Phase 20 or earlier).

Bournonite: A sulfosalt containing lead, copper, and antimony, bournonite has the formula PbCuSbS₃ and typically comprises at least 40 % lead and 13 % copper. Two samples of bournonite were analyzed, one of which was obtained from the 2006 excavation pit, corresponding to an early phase (pre-dating Phase 20).

Malachite: A hydrated copper carbonate (Cu₂(OH)₂CO₃), malachite was widely smelted during the Chalcolithic period due to its high copper content (over 55 %) and ease of reduction. The malachite sample, dating to an early phase (Phase 20 or earlier), was found at the Planet site in small fragments weighing only a few grams. These fragments are either very pure or have quartz and iron oxide gangue. Malachite is sometimes associated with sulfide, which is part of the original unaltered copper mineralization.

Bindheimite: Identified for the first time at a Chalcolithic site, bindheimite is a partially hydrated lead-antimony oxide (Pb₂Sb₂O₆(O, OH)). This bright yellow mineral, easily identifiable in the field, was found throughout the stratigraphic layers of the Planet site (Phase 20 or earlier). Elemental analysis by electron microscopy and crystallographic confirmation via X-ray diffraction revealed its chemical structure. Bindheimite often appears alongside malachite, forming a yellow-green variegated pattern. The mineralized core may also contain small inclusions of bournonite grains.

Together, these mineral species may constitute a true copper-lead ore, providing the mineral charge for the metallurgical practices at the Planet site. As we have observed, the previously described sulphide and oxidized ores are naturally associated within the veins, and therefore within the metallurgical process. We were able to demonstrate this through the study of various elements detailed below, such as the slag (Costa et al., 2021).

### 3.2. Slag

Six slag samples from different archaeological levels were analyzed, ranging from Phase 4 to Phase 20 or earlier. These samples span all identified occupational phases of the site. Based on chemical composition and physical characteristics, the slag was divided into two main categories (Costa et al., 2021), both of which are present together throughout all the excavation phases identified to date:

- Yellow, Powdery Slag: This slag is rich in lead and antimony, indicating the reduction of lead-bearing ores, particularly bournonite and bindheimite;

- Reddish, Vitrified Slag: Characterized by a high copper content, this slag reflects the reduction of copper-bearing ores such as tetrahedrite and malachite

### 3.3. Metal artifact

An unshaped metal artifact (phase 9) weighing 49 g was analyzed. This object, classified as an ingot, has a distinctive melted, patty-like appearance with small beads around its edges. The artifact features two visibly different patinas: one side exhibits a bright white, lead-rich surface, while the other has a green to grayish patina, indicating a higher concentration of copper and silver. Chemical analysis (SEM) of a micro-sample revealed a high lead content (70–80 %) with minor copper (a few percent). Surface X-ray fluorescence analysis provided further insights into the composition of this two-phase artifact (Table 1), revealing
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Samples from the Planet metallurgical site analyzed in this study: (a) Sample US2173 PT2309: Malachite and bournonite. (b) Sample FS2006 REF98: Tetrahedrite. (c) Sample US2098 PT1660: Bournonite. (d) Sample US4061 PT3385: slag from a furnace sample. (e) Sample US4019 PT3097 slag from a furnace sample. (f) Sample us 4035pt 3183: slag. (g) Sample US4041 PT3263: Ingot.</figcaption></figure>
<table><caption>Table 1<br>XRF data showing the elemental composition of the ingot.</caption><thead><tr><th>Site</th><th>Artefact</th><th>Side</th><th>Cu</th><th>Cu Err</th><th>Sn</th><th>Sn Err</th><th>Pb</th><th>Pb Err</th><th>Ag</th><th>Ag Err</th><th>As</th><th>As Err</th><th>Bi</th><th>Bi Err</th><th>Co</th><th>Co Err</th><th>Fe</th><th>Fe Err</th><th>Ni</th><th>Ni Err</th><th>Sb</th><th>Sb Err</th><th>Au</th><th>Au Err</th><th>S</th><th>S Err</th><th>Zn</th><th>Zn Err</th></tr></thead><tbody><tr><td>Le Planet</td><td>lingot</td><td>Bottom side</td><td>26.10</td><td>0.0647</td><td>1.10</td><td>0.105</td><td>20.59</td><td>0.1539</td><td>38.53</td><td>0.1411</td><td>&lt; LOD</td><td>0.0221</td><td>0</td><td>0</td><td>&lt; LOD</td><td>0.0035</td><td>1.86</td><td>0.0267</td><td>0.012</td><td>0.0027</td><td>&lt; LOD</td><td>0.0276</td><td>0.02</td><td>0.0146</td><td>&lt; LOD</td><td>0.0138</td><td>0.014</td><td>0.0043</td></tr><tr><td>Le Planet</td><td>lingot</td><td>Top side</td><td>6.33</td><td>0.033</td><td>1.90</td><td>0.0995</td><td>64.53</td><td>0.285</td><td>19.05</td><td>0.1189</td><td>&lt; LOD</td><td>0</td><td>2.24</td><td>0.0499</td><td>&lt; LOD</td><td>0</td><td>1.04</td><td>0.0231</td><td>0.005</td><td>0.0021</td><td>3.00</td><td>0.0814</td><td>&lt; LOD</td><td>0</td><td>&lt; LOD</td><td>0.0234</td><td>0.005</td><td>0.003</td></tr></tbody></table>

notable surface effects associated with silver. Analysis confirmed that the ingot is composed of two superimposed metal layers, possibly created by two-stage casting or by the natural segregation of lead and copper during slow cooling. This latter phenomenon (Baron and Cochet, 2003), essentially occurs due to the immiscibility of Pb in copper and the different melting points of the two metals, resulting in their separation upon cooling.

# 4. Results and discussion

## 4.1. The Planet site production

The isotopic results from samples at the Planet workshop (Table 2) are largely consistent across different sample types, including ores, slag, and ingots, with standard deviations for individual isotope ratios ($^{206}$Pb/$^{204}$Pb, $^{207}$Pb/$^{204}$Pb, and $^{208}$Pb/$^{204}$Pb) typically below 0.001 (2 SE), indicating a high degree of internal consistency. This uniformity in isotope ratios across all metallurgical process materials strongly suggests that the ore sources were either the same deposit or deposits with highly similar isotopic signatures. The consistent isotopic match between ore samples and slag further supports the idea that these local ores were preferentially smelted on-site. This alignment between geological raw materials and metallurgical waste bolsters previous analyses of mineralogy and elemental composition for slag and metal artifacts found on the site.

The results show that the polymetallic ores processed at the Planet site—primarily tetrahedrite, bournonite, and malachite—exhibit isotopic homogeneity, supporting the hypothesis that they could originate from a single, polymetallic deposit.

However, the FS 2006 (PT43) bournonite sample differs isotopically from the other samples, suggesting either the use of alternative supply sources during certain occupational phases or an internal variation within the source deposit itself. This isotopic deviation prompts further inquiry into the chronological context of these materials and encourages ongoing mineral and mining archaeology to understand the source of variability.

The lead ingot recovered from the site is isotopically consistent with the slag, indicating that it too originated from Planet ore reduction processes.

## 4.2. Local mineralization

This study represents the first isotopic characterization of a pre-protohistoric metallurgical workshop producing both copper and lead, offering valuable insights into the coherence of supply sources relative to the surrounding mineralogical environment.

In the Fayet District, which historically lacked an isotopic reference for copper deposits, the discovery of the Planet metallurgical site has created a valuable opportunity to explore copper and lead sourcing within a poorly documented pre-protohistoric mining complex. An initial goal was to catalogue regional deposits (Costa and Maillé, 2022). Although the analysis of archaeological contexts, mineral characterizations, and elemental compositions of artifacts has provided valuable information, these methods alone do not offer the resolution needed to pinpoint precise ore sources. To address this, we initiated systematic sampling in historical mining locations within the district to create a preliminary isotopic reference system for nearby copper and lead ores. Our aim was to compare the isotopic signatures of artifacts, slags, and ores found at the Planet site with those from local deposits.

Preliminary data reveal that the isotopic signatures of local deposits are generally consistent across the region, with the exception of Verrières, which differs due to its unique geological context (Fig. 2, Table 3). When plotted (Fig. 5), these data suggest several potential ore sources for the Planet site, yet none of the sampled deposits exactly matches the Planet site's signature. To date, we do not have sufficient data to assess the variability within each deposit. In this study, we
<table><caption>**Table 2**
Lead isotope data obtained from the material analyzed at the Planet site.</caption><thead><tr><th>Sample</th><th>Site</th><th>Sample nature</th><th>note</th><th>Phase</th><th>206Pb/204Pb</th><th>2 Se</th><th>208Pb/204Pb</th><th>2 Se</th><th>207Pb/204Pb</th><th>2 Se</th></tr></thead><tbody><tr><td>A-BRN 2</td><td>Planet</td><td>Bournonite</td><td>US2098 PT1660</td><td>15 to 20</td><td>18.240</td><td>5E-04</td><td>38.254</td><td>0.002</td><td>15.661</td><td>6E-04</td></tr><tr><td>SL-4</td><td>Planet</td><td>Slag</td><td>US4035 PT3183</td><td>6</td><td>18.247</td><td>6E-04</td><td>38.254</td><td>0.002</td><td>15.658</td><td>7E-04</td></tr><tr><td>A-TET</td><td>Planet</td><td>Tetrahedrite</td><td>FS2006 PT 98</td><td>>20</td><td>18.249</td><td>6E-04</td><td>38.258</td><td>0.002</td><td>15.659</td><td>7E-04</td></tr><tr><td>A-MAL</td><td>Planet</td><td>Malachite and bindheimite</td><td>US2173 PT2309</td><td>>20</td><td>18.240</td><td>6E-04</td><td>38.266</td><td>0.002</td><td>15.662</td><td>7E-04</td></tr><tr><td>SL-2</td><td>Planet</td><td>Slag</td><td>US2187 PT2373</td><td>15 to 20</td><td>18.252</td><td>7E-04</td><td>38.272</td><td>0.002</td><td>15.664</td><td>7E-04</td></tr><tr><td>SL-2 dup</td><td>Planet</td><td>Slag</td><td>US2187 PT2373</td><td>15 to 20</td><td>18.249</td><td>0.001</td><td>38.263</td><td>0.002</td><td>15.662</td><td>0.001</td></tr><tr><td>SL-5</td><td>Planet</td><td>Slag</td><td>US4061 PT3385</td><td>6</td><td>18.257</td><td>8E-04</td><td>38.276</td><td>0.003</td><td>15.663</td><td>8E-04</td></tr><tr><td>SL-1</td><td>Planet</td><td>Slag</td><td>US 2091 PT2251</td><td>>20</td><td>18.258</td><td>5E-04</td><td>38.276</td><td>0.002</td><td>15.664</td><td>5E-04</td></tr><tr><td>SL-3</td><td>Planet</td><td>Slag</td><td>US4018 PT3097</td><td>4</td><td>18.260</td><td>6E-04</td><td>38.287</td><td>0.002</td><td>15.666</td><td>6E-04</td></tr><tr><td>ING</td><td>Planet</td><td>Ingot</td><td>US 4041 PT3263</td><td>9</td><td>18.258</td><td>7E-04</td><td>38.288</td><td>0.002</td><td>15.664</td><td>7E-04</td></tr><tr><td>A-BRN 1</td><td>Planet</td><td>Bournonite</td><td>FS2006 PT 43</td><td>>20</td><td>18.340</td><td>7E-04</td><td>38.416</td><td>0.002</td><td>15.671</td><td>7E-04</td></tr></tbody></table>

<table><caption>**Table 3**
Lead isotope data acquired from deposits near the Planet site.</caption><thead><tr><th>Sample name</th><th>Mine</th><th>Minerals</th><th>206Pb/204Pb</th><th>2 Se</th><th>208Pb/204Pb</th><th>2 Se</th><th>207Pb/204Pb</th><th>2 Se</th></tr></thead><tbody><tr><td>Brn-Mo-S</td><td>Mourgis</td><td>bournonite</td><td>18.255</td><td>4E-04</td><td>38.297</td><td>0.002</td><td>15.666</td><td>5E-04</td></tr><tr><td>Mal-Po</td><td>Pourtel</td><td>malachite</td><td>18.271</td><td>5E-04</td><td>38.348</td><td>0.002</td><td>15.667</td><td>6E-04</td></tr><tr><td>Tet-BP</td><td>Bouco Payrol</td><td>tetrahedrite</td><td>18.280</td><td>6E-04</td><td>38.287</td><td>0.002</td><td>15.664</td><td>6E-04</td></tr><tr><td>Az-HF</td><td>Hautes Fages</td><td>azurite</td><td>18.302</td><td>5E-04</td><td>38.328</td><td>0.002</td><td>15.668</td><td>6E-04</td></tr><tr><td>Cy-Rieu</td><td>Rieucros/Faveyrolles</td><td>chalcopyrite</td><td>18.365</td><td>5E-04</td><td>38.316</td><td>0.002</td><td>15.669</td><td>6E-04</td></tr><tr><td>Bind-LB-D</td><td>La Baume</td><td>bindhemite + malachite</td><td>18.368</td><td>6E-04</td><td>38.409</td><td>0.002</td><td>15.675</td><td>7E-04</td></tr><tr><td>Bind-PR</td><td>Puech de Roste</td><td>bindhemite</td><td>18.385</td><td>6E-04</td><td>38.382</td><td>0.002</td><td>15.676</td><td>6E-04</td></tr><tr><td>Cy-Ve</td><td>Verrieres</td><td>chalcopyrite</td><td>18.415</td><td>6E-04</td><td>38.623</td><td>0.002</td><td>15.647</td><td>6E-04</td></tr><tr><td>Tet-LB</td><td>La Baume</td><td>tetrahedrite</td><td>18.452</td><td>0.002</td><td>38.367</td><td>0.019</td><td>15.677</td><td>0.001</td></tr><tr><td>Mal-PR</td><td>Puech de Roste</td><td>malachite</td><td>18.476</td><td>5E-04</td><td>38.428</td><td>0.002</td><td>15.679</td><td>6E-04</td></tr><tr><td>Tet-Cr</td><td>Cribas</td><td>tetrahedrite</td><td>18.492</td><td>8E-04</td><td>38.509</td><td>0.002</td><td>15.679</td><td>7E-04</td></tr></tbody></table>

focused on evaluating the isotopic diversity within a radius of about 5 km around the site, as there is no deposit directly linked to the workshop.

The Mourgis deposit shows the closest match both mineralogically (Costa et al., 2021) and isotopically. The isotopic properties, particularly of the Mourgis deposit, will require further investigation, as this new isotopic analysis is the closest to those from the Planet site, followed by the Bouco Payrol and Pourtel deposits.

However, fully identifying the specific origins of the ore will require additional systematic sampling and analysis, particularly of complex nearby deposits hosted in hydrothermal breccias. It is possible that the ores smelted at Planet correspond to a distinct mineralization deposit in the region.

Although certain mineralogical associations observed at La Baume initially appeared similar to those at the Planet site, they differ in key ways. The absence of mercury in Planet site ores, an element prevalent in the La Baume deposit, distinguishes the two sources (Maillé, 2018). Additionally, a sample of bournonite from the Planet site stands out isotopically from other ores and slags recovered there. This unique sample suggests a potentially different origin, possibly linked to deposits like La Baume or Puech de Roste, both of which exhibit signs of ancient mining. Future work should focus on these deposits to refine our understanding of the sourcing of materials used at the Planet site. One nearby deposit, Lacan, located 1.5 km south of the Planet site, is a promising target for further analysis due to its association fahlore minerals with bournonite and copper oxide, as documented by the BRGM

<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Fayet/Cénomes and Planet site lead isotope data acquired in this study.</figcaption></figure>
Distribution of isotopic analyses in the southern Massif Central

<figure><img src="image_9.png" /><figcaption>Fig. 6. Map illustrating the distribution of all regional lead isotope data in comparison with copper deposits and data from this study (Geological map: Faure and al., 2009).</figcaption></figure>

<table><caption>**Table 4**
Lead isotope data acquired from regional deposits.</caption><thead><tr><th>Mine</th><th>Minerals</th><th>208/204</th><th>2se</th><th>207/204</th><th>2se</th><th>206/204</th><th>2se</th></tr></thead><tbody><tr><td>Bleymard</td><td>Galena</td><td>38.703</td><td>0.003</td><td>15.686</td><td>0.0007</td><td>18.554</td><td>0.0009</td></tr><tr><td>Vialas</td><td>Galena</td><td>38.794</td><td>0.007</td><td>15.691</td><td>0.0009</td><td>18.567</td><td>0.0011</td></tr><tr><td>Sainte Lucie</td><td>Galena</td><td>38.736</td><td>0.008</td><td>15.686</td><td>0.0009</td><td>18.628</td><td>0.0012</td></tr><tr><td>Malines</td><td>Galena</td><td>38.504</td><td>0.005</td><td>15.676</td><td>0.0007</td><td>18.402</td><td>0.0009</td></tr><tr><td>Malines dup</td><td>Galena</td><td>38.510</td><td>0.004</td><td>15.677</td><td>0.0007</td><td>18.403</td><td>0.0008</td></tr><tr><td>Ceilhes</td><td>Bournonite and Barytine</td><td>38.555</td><td>0.004</td><td>15.686</td><td>0.0008</td><td>18.384</td><td>0.0009</td></tr><tr><td>Saint Laurent le Minier</td><td>Bournonite and Barytine</td><td>38.508</td><td>0.004</td><td>15.679</td><td>0.0009</td><td>18.410</td><td>0.0010</td></tr><tr><td>La Sanguinède</td><td>Bournonite</td><td>38.515</td><td>0.003</td><td>15.679</td><td>0.0007</td><td>18.445</td><td>0.0008</td></tr><tr><td>La Sanguinède dup</td><td>Bournonite</td><td>38.520</td><td>0.005</td><td>15.680</td><td>0.0007</td><td>18.459</td><td>0.0008</td></tr><tr><td>La corne des causses</td><td>Bournonite and Barytine</td><td>38.553</td><td>0.005</td><td>15.685</td><td>0.0006</td><td>18.388</td><td>0.0008</td></tr></tbody></table>

(Donnot et al., 1982). While some old trenches are visible there, dense vegetation and colluvium obscure parts of the deposit, making prospecting challenging. Analysis of samples from this deposit could provide crucial data on local copper sourcing.

### 4.3. Regional mineralization

In this section, we aim to determine whether the metallurgical workshop at Le Planet stands out from the regional data and whether it will eventually be possible to trace the workshop's productions by comparing them with regional ores. This applies not only to copper production, but also to lead. Across the region, isotopic studies have largely focused on lead ores, leaving copper deposits under-documented (Fig. 6). Only the Cabrières and now the Planet mining complexes have copper-specific isotope data. This imbalance is partly due to the concentration of previous research in the Massif Central (Marcoux, 1986) in particular works around Mont Lozère (Baron et al., 2006) in Cévennes and the Montagne Noire (Stos-Gale, 1992). Les Malines mine alone

accounts for 63 analyses, nearly half of the region's available data (Guen et al., 1991). Meanwhile, several mineralized areas with evidence of ancient metallurgy, including the Villefranche de Rouergue fault (Al Claus site: Carozza et al., 1997), Corbières (Mantenant et al., 2013), the Orb Valley, eastern Pyrenees, Lacaune mountains, and the northern slopes of the Montagne Noire, remain largely unstudied. Due to the simultaneous presence of the two metallurgies at the archaeological site of Planet, we sought to compare our newly generated dataset with previously published data. For this purpose, we included some bournonite samples as well as galena samples. This was done notably for deposits rich in bournonite, such as Les Malines, which has already been well studied, as well as for a set of deposits dominated by galena (Guen et al., 1991).

For this study, we analyzed a small number of regional minerals, including bournonite samples within a 50–100 km radius of the Planet site (Table 4). These lead-based ores, with one source located approximately 15 km from the site at Ceilhes, exhibit isotopic homogeneity comparable to previous data. Our study contributes new data from the
<figure><img src="image_10.png" /><figcaption>**Fig. 7.** Lead isotope data obtained in this study, compared with regional data from previous studies (Baron et al., 2006; Brévart et al., 1982; Guen et al., 1991; Le Guen et al., 1992; Marcoux, 1986; Stos-Gale et al., 1995; Stos-Gale and Gale, 2009).</figcaption></figure>
Fayet/Cénomes sector (Table 3), an area with previously only three documented analyses (Brusque, Cusses), which shows similarity to those in the Montagne Noire ($^{206}$Pb/$^{204}$Pb < 18) and one mineralization phase at Salsigne or Bibaud (Le Guen et al., 1992). Newly acquired data (Fig. 7) represent a range of polymetallic mineralization from the southern Massif Central (Les Malines, Mont Faulat, Salsigne), which were rich in copper, lead, antimony, and silver and served as primary sources of raw material in the Late Neolithic (Ambert et al., 1998; Costa et al., 2021; Espérou, 1992).

The new data concerning galena from more distant deposits, poorer in polymetallic sulfosalts, stand out clearly based on the $^{208}$Pb/$^{204}$Pb (>38.7) and $^{206}$Pb/$^{204}$Pb (>18.5) ratios, confirming the validity and comparability of the datasets. This highlights the importance of a mineralogical approach when addressing archaeological questions and the need for careful consideration of reference frameworks used in artefact provenance studies. The data from the Fayet/Cénomes geologial district align well with the regional dataset from the Montagne Noire/Cévennes area. Although the data from the Planet site are compatible with this group, they also suggest supply from older mineralization linked to the polymetallic systems of the Montagne Noire, such as the Salsigne mine, which is characterized by multiple phases of mineral deposition (Demange et al., 2006).

This study highlights the need for comprehensive documentation of these polymetallic veins and better characterization of deposits with multiple mineralization phases, as seen at Salsigne (Demange et al., 2006; Le Guen et al., 1992). Given that metallurgical processes may involve mixing ores with varied isotopic signatures, the resulting isotopic signatures in artifacts can differ from the geological data. Therefore, establishing repositories linked to specific metallurgical workshops is essential (Fig. 7), as these locations are where mixing typically occurs. While studies of the Planet workshop and its immediate environment are still in preliminary stages, future research should further investigate the site's different phases of activity and nearby deposits. It is in this context that the new data (Tables 2 and 3) enable the establishment of a coherent reference framework for future archaeological work both at the site and locally in the study of archaeological copper and lead artifacts.

This initial isotopic characterization generates data within an isotopic field that is distinguishable from those previously produced in the southern Massif Central. To date, only the Salsigne deposit appears isotopically close to the workshop data. However, this isotopic similarity should be nuanced by differences in elemental composition. Indeed, the Salsigne District is characterized by copper deposits with high concentrations of arsenic, bismuth, and gold (Demange et al., 2006), whereas the ores processed at the Planet workshop and its geological sector are marked by the combined presence of copper, antimony, silver, and lead (Costa et al., 2021; Espérou, 1992; Leblanc, 1997). This highlights that isotopic data alone are not sufficient for resolving archaeometallurgical provenance questions, which will require multidisciplinary investigations moving forward.

## 5. Conclusion

The Planet metallurgical site offers crucial insights into late Neolithic metallurgy in southern France, presenting a unique setting where lead-rich artifacts coexisted alongside copper artifacts. The Planet workshop stands out for its remarkable preservation, with intact reduction furnaces and a complete production chain, allowing a coherent comparison of each element within the metallurgical process to the extensive local metalliferous resources. Through in-depth analysis of ores, metallurgical residues, and metal artifacts, we have characterized the Planet workshop from both mineralogical and isotopic perspectives. Additionally, this study enables the first isotopic analysis of lead and copper ores deposits in the region, many of which have documented histories of exploitation from as early as the Chalcolithic period.

This first isotopic characterization of the Planet workshop provides valuable reference data on the site's resource base. It also establishes a

benchmark for comparing isotopic signatures associated with metallurgical workshops, demonstrating a high degree of homogeneity across the isotopic profiles of the Chaîne Opératoire elements. This first batch of local ore analyses reveals compatibility between the workshop's isotopic signature and that of the Cénomes/Fayet sector, suggesting a significant concentration of metallurgical activity in this area during the late Neolithic. This metallurgical dynamism highlights the role of the southern Massif Central and Aveyron in exploiting metalliferous resources in this period.

Further research is essential to deepen our understanding of the significance of these metallurgical activities and to explore the broader regional structures that may have supported them.

## CRediT authorship contribution statement

**K. Costa:** Writing – review & editing, Writing – original draft, Supervision, Project administration, Formal analysis, Conceptualization.

**C. Tomczyk:** Writing – review & editing, Writing – original draft, Funding acquisition, Formal analysis. **G. Artioli:** Writing – review & editing, Writing – original draft, Validation, Methodology, Formal analysis. **C. Canovaro:** Writing – original draft, Validation, Methodology, Formal analysis. **C. Chauvel:** Writing – review & editing, Writing – original draft, Validation, Methodology, Formal analysis. **P. Gutiérrez:** Writing – original draft, Validation, Methodology, Formal analysis. **M. Maille:** Writing – review & editing, Writing – original draft, Supervision, Project administration.

## Funding

Ministère (SRA), Région et Département. Université Paris 1.

## 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.

## Acknowledgements

The authors would like to thank the members of the PCR and the excavation teams without whom this study would not have been possible. We would also like to thank the Collège des écoles doctorales of Paris 1 University 1 for the international mobility grant awarded to C. Tomczyk in 2019 to carry out the preparation of the lead isotope analyses at the University of Padua. The authors would like to thank Daniel Neuville who took us to the mineralogy museum and helped selecting ores even though it was originally for other reasons. Part of this work was supported by IPGP multidisciplinary program PARI, by the Region Ile-de-France SESAME Grants no. 12015908 and EX047016 and by the IdEx Université de Paris grant ANR-18-IDEX-0001.

## Data availability

Data will be made available on request.

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