Archaeometric contribution to the interpretation of the Late Bronze Age "hoard" from Porto do Concelho (Mação, Central Portugal)

Abstract

This paper presents and discusses the results of the multi-analytical study carried out on a group of 39 Late Bronze Age artefacts from the site of Porto do Concelho, Central Portugal. The chemical composition of the objects was determined by Energy Dispersive X-ray Fluorescence (EDXRF) and their microstructural features were identified by Optical Microscopy (OM) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS). The results show that metals are binary alloys (Cu+Sn) and leaded bronzes (Cu+Sn+>2.0 wt.% Pb), with a variable content of impurities, such as Pb (when lower than 2.0 wt.%), Fe, As, Ag, Sb and Ni. The microstructural characterization carried out on 21 artefacts allowed the identification of two main operational sequences: 10 objects show a dendritic microstructure suggesting that metals have not undergone any post-casting treatment; 11 artefacts display the presence of annealing twins with, in some cases, slip bands, resulting from the application of thermal and mechanical treatments. The analytical results are compared to those of other metal collections from regional LBA, and together with the bibliographic information available become an opportunity to question and rediscuss the real nature of a collection of metals that most of archaeologists consider as a typical LBA founder's hoard.