Slag from Modern Copper Production Found in Bergwerk, Burgenland, Austria

The investigated slags from Bergwerk (Burgenland, Austria) are from the 17th century and a byproduct of a copper smelting process. These slags are typical plate slags but metallographic studies have shown that these slags are atypical compared to alpine slags. There is an elongated texture running across the slag but the typical fayalite dendrites are absent. Noticeable are high sulfur and Fe levels. SEM-EDX element mappings show that FeO and FeS coexist locally, suggesting that a eutectic FeO-FeS mixture exists. The melting point could have been lowered to 930 °C by the FeO-FeS eutectic. CaSO4 was also detected in the slag. The glass phase, containing all the slag impurities, is located between the fayalite and the FeO-FeS mixture. The smelting process, in which these slags were formed, is currently unknown. It has been unproven as well, what advantages such a copper smelting process could have.