Reconstruction of Copper Smelting Technology Based on 18–20th-Century Slag Remains from the Old Copper Basin, Poland

This research was conducted on historical copper slags from Leszczyna and Kondratow in Lower Silesia, Poland. The area, formerly known as the Old Copper Basin, was a mining and smelting centre between the 18th and 20th centuries, with a dominant period in the 19th century. Cu-carbonates and residual chalcocite dominate local strata-bound copper deposits. Ore bodies are restricted to carbonate strata. A geochemical and mineralogical study of slag samples from four research sites allowed us to establish that a low amount of sulphur in slags results from S-poor ores, and pyrite with gypsum was implemented as reducing agents. Arkose sandstones served as a flux. During smelting, oxygen availability was limited, and temperature exceeded 1200 °C (18th- and 19th-century smelting) and 1400 °C (20th-century smelting). Calculated viscosity indexes mark the low efficiency of metal separation between the silicate and metallic phases. The skeletal and dendritic form of the crystals proved that slag melt was relatively rapidly cooled after formation, usually in air conditions. We estimated that approx. 2000 m3 of slag was created during the leading smelter (Stilles Gluck) activity. The research provided various details of the historical copper smelting technological process in Leszczyna and Kondratow.