<p>Andros Island is situated in Cyclades, Aegean Sea, Greece and is mainly composed of blueschists and marbles of the Attico-Cycladic Massif with subsidiary basic-ultrabasic igneous rocks. Iron ores have been located close to Palaeopolis and in the villages of Agios Petros and Mpatsi to the northwest. Iron-rich minerals found in the area include limonite, goethite, hematite, and siderite in the form of veins in marbles or on the contact of marbles with the schists. According to the findings of recent excavations metallurgical slags have been discovered in several archaeo-stratigraphic layers. The aim of the present paper is to characterize the newly discovered slags through identification of synthetic mineral phases formed during the metallurgical processes and measurement of their trace element content in order to consider the metal extracted, the origin of the source ore used, the metallurgical process followed, and the political/military status at the time of mining/metallurgical operations. The synthetic mineral phases of the slag such as wüstite, bustamite, tephroite and fayalite are largely a product of the iron ore chemistry which is partially Mn-Ba-rich, components that were acted as fluxes to make this iron. The morphologies and abundance of the phases identified reflect thermochemical processes occurring both during smelting and during secondary working in the smithing hearth. However, based on the ternary FeO (+ CaO+MnO) -Al₂O₃-SiO₂ diagram, the slags studied have rather been derived during smithing processes. At present, it is not possible to link these metallurgical processes to specific military or political contexts, as this would require a fuller understanding of the entire technological system, including relationships between primary iron producers, the exchange of iron semi-products, the artefact producers, and the implements that were made.</p>