A first appraisal on copper sources for Chalcolithic settlements in southern Portugal using Pb isotope analysis

Abstract

This work presents the first provenance study on copper in use by 3rd millennium BC communities in southern Portugal. Copper ores from small mines and copper artefacts from Chalcolithic settlements were subjected to Pb isotope analysis. Some of Pb isotope ratios obtained in ores from the Ossa-Morena Zone, but also from the South Portuguese Zone, evince the existence of deposits with highly radiogenic Pb, which was previously considered rare in the Iberian Peninsula. Pb isotope ratios of artefacts were compared with Pb isotope fields of closer geological/tectonostratigraphic zones, namely the South Portuguese Zone, Ossa-Morena Zone and Central Iberian Zone. The assessment suggests that most artefacts were produced with copper from the Ossa-Morena Zone. Nevertheless, a flat axe of the Três Moinhos settlement is a remarkable exception due to its highly radiogenic Pb signature, which only has parallels in the Iberian Peninsula on copper ores of the Chalcolithic mines of La Profunda and El Milagro (northern Spain). Consequently, this flat axe constitutes the first indication of a possible long-distance trade of copper between the Cantabrian region and southwestern Iberian Peninsula during the 3rd millennium BC.