Elemental and isotopic composition of bronze axes from Léon (France)

This dataset contains analyses of 31 copper-alloy axes from Léon (Landes, France).

Material

31 copper-alloy axes were analyzed. Each artefact was weighed, photodocumented, and 3D digitized before sampling. Each artefact was sampled twice using a single-use saw blade. The first sample was taken from the heel of the axes, after which the surface was mechanically cleaned to remove surface corrosion. These samples were used to measure lead isotope ratios. The second sample, a few cubic millimeters in size, was taken from the edge of the blades. These micro-samples were mounted, then ground and polished to a 0.25 mm diamond finish to create a surface suitable for SEM-EDS analyses.

Energy dispersive X-ray spectrometry

The elemental composition of the samples was obtained by energy-dispersive X-ray fluorescence spectrometry using two Oxford Ultim Max 100 spectrometers, coupled with scanning electron microscopy imaging (JEOL JSM IT500HR variable-pressure microscope). Measurements were carried out under a partial vacuum (20 Pa) with an acceleration voltage of 20 kV to avoid charging phenomena. The acquisition time was 60 seconds per spectrum over the 0-20 keV energy range. For all EDS spectra, the dead time during acquisition was around 30%, with an average number of counts per spectrum greater than 106.

Due to the presence of arsenic (As) and lead (Pb) in the same samples, the As L ray series and the Pb M ray series were used for EDS analyses to avoid line overlap with the As K ray series and Pb L ray series. Six measurements were carried out on each sample, with the area analyzed in each measurement being approximately 5.10-2 mm². For each sample, the compositional mean (Aitchison 1986) of the six measurements was used. Results are expressed as mass percentages, normalized to 100%. Values below 0.5% should be interpreted with caution, but they are retained in the general composition as they provide qualitative information.

The file leon_elements.csv contains all elemental compositions, with the following columns:

• code: sample reference.
• O,Mg,Al,Si,S,Fe,Ni,Cu,Zn,As,Sn,Pb: amounts (%)

Multi-collection mass spectrometry

Lead isotope ratios were measured by multi-collection inductively coupled plasma mass spectrometry (MC-ICP-MS) at the Service d'Analyse des Roches et Minéraux (SARM) of the Centre de Recherches Pétrographiques et Géochimiques (UMR 7358 CRPG).

Samples were weighed into 15 mL Savillex vial, and HNO3 was added. The solution was heated at 115°C for at least 72 hours, evaporated, then mixed with HCl and heated again for 24 hours or until the sample was completely dissolved. After evaporation, 1 mL of 0.8 M HBr was added to place the sample in the same medium as that used in the ion exchange column.

Each sample was loaded onto approximately 50 microliters of AG1X8 resin in micro-columns (see Manhes et al. 1980), then 2 mL of 0.8 M HBr were used for elution. Lead was collected in 2 mL of 6M HCl (4 x 0.5 mL), dried, and redissolved in 1 mL of 0.5 M HNO3.

Pb analyses were performed on an MC-ICP-MS (Neptune Plus, Thermo Electron) using Tl (NIST 997) as an external standard for mass bias (White, Albarède, and Télouk 2000). The Tl and Pb values used for NIST 981 are those of Thirlwall (2002).

The file leon_isotopes.csv contains all lead isotopes ratios, with the following columns:

• CRPG, BDX: sample references.
• Pb_206_204, Pb_206_204_error: 206Pb/204Pb ratio and error.
• Pb_207_204, Pb_207_204_error: 207Pb/204Pb ratio and error.
• Pb_208_204, Pb_208_204_error: 208Pb/204Pb ratio and error.
• Pb_207_206, Pb_207_206_error: 207Pb/206Pb ratio and error.
• Pb_206_207, Pb_206_207_error: 206Pb/207Pb ratio and error.
• Pb_208_206, Pb_208_206_error: 208Pb/206Pb ratio and error.