The ancient slags of Palaeopolis, Andros Island, Greece. Geochemical and mineralogical characterization, archaeometallurgical and archaeoeconomic implications

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 north. 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, thephroite and fayalite are largely a product of the ore chemistry and Mn-Ba rich fluxes that were used to make this iron. Phase forms and abundance are the result of complex thermochemical dynamics that existed both in the smelting furnace and later in the blacksmith’s hearth. Whether or not artifacts and the processes that created them were connected in some direct way with military or political actions cannot be determined without an additional 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.