Reconstruction of smelting conditions during 16th-to 18th-century copper ore processing in the Kielce region (Old Polish Industrial District) based on slags from Miedziana Gora, Poland

This study presents the first reconstruction of the smelting conditions in 16th- to 18th-century smelters from Miedziana Gora (Holy Cross Mountains, Poland). Based on geochemical (inductively coupled plasma mass spectrometry/emission spectrometry, X-ray fluorescence) and mineralogical analysis (X-ray diffractometry, scanning electron microscopy, electron probe micro-analysis) of historical slags, their chemical/phase composition and the basic smelting parameters (temperature, melt viscosity, and oxygen fugacity) were determined. Due to the differences in chemical and phase composition, slags from different smelting stages have been distinguished: hypocrystalline slags (MG6) from speiss/matte production and glassy (MG1-MG5) from matte conversion. In glassy slags, pyroxenes, quartz/cristobalite grains, and aggregates composed of metallic Cu and PbO are dispersed in the glass. Hypocrystalline slags are composed of wollastonites, anorthites, and metallic Cu. The temperature range at which the slags were formed was from similar to 1100 degrees C (solidus temperature) to 1150-1200 degrees C (liquidus temperature). The silicate melt's viscosity was from log eta = 1.19 to 4.42 Pas (at 1100-1200 degrees C). The higher viscosity of MG1-MG5 slags indicates that, unlike MG6 slags, they were not formed during gravity separation. Information about the phase composition made it possible to determine the oxygen fugacity in the range of log fO(2) = -4 to -12 atm. High oxygen fugacity indicates the oxidizing nature of the smelting process.