Early Iron Age metal trade networks of the workshop of Cabeço Redondo (southern Portugal). Tracing the origin of lead of ternary bronzes

Abstract

Recent research has identified two regions for the supply of copper to the 5th century workshop of Cabeço Redondo (Moura), namely Sardinia (Central Mediterranean region) and Los Pedroches Batholith complex (Central Iberian Zone). The important collection of metal debris recovered by archaeological surveys includes not only copper and bronze ingots and lumps, but also leaded bronze examples, which study can provide answers regarding the provenance of lead of ternary bronzes. Therefore, a fragment of a possible ingot and two lumps were characterised by SEM-EDS, ICP-QMS and MC-ICP-MS to establish microstructural features, trace elemental compositions and Pb isotope signatures, respectively. Leaded bronze samples show similar microstructural compositions, comprising a dendritic morphology with significant presence of the α + δ eutectoid and Pb-rich and Cu-S inclusions. Trace elements profiles indicate a higher Ni and As content in the “ingot”. The Pb isotope signature of this “ingot” is also significantly different from that of the two lumps, but all of them overlap with lead sources from different regions bordering the Mediterranean Sea. Therefore, the determination of the nearest Euclidean neighbours and geologic parameters, crossed with archaeological and historical data, was used to find the most likely sources of lead of these ternary bronzes. The lead sources could correspond to distinct regions in the Iberian Peninsula (Ossa-Morena Zone and Alcudia Valley) and in the Eastern Mediterranean (Greece and Anatolia). Considering also the sources of copper for the Cabeço Redondo metallurgical workshop, these new results evidence a complex metal supply system that includes both intra and extra-peninsular trade networks covering, not only the Western and Central Mediterranean, but also Eastern Mediterranean regions.