Archaeometallurgic slags from Kutna Hora

The polymetallic mineralisation of the Kutná Hora ore district (Czech Republic) has been successfully exploited for silver production, specially during the 14th and 15th centuries. Five slags, sampled from the Vrbovy mlýn smelting centre, have been analysed by X-ray fluorescence spectrometry, X-ray powder diffraction, optical microscopy, scanning electron microscopy and energy dispersive X-ray spectrometry. The slags are mostly composed of SiO2, FeO, CaO and minor amounts of Al2O3; important sulphur and zinc contents were detected. Depending on the calcium content, two main pyrometallurgical phase assemblages were identified, i.e., ferrobustamite + hedenbergite vs. hedenbergite + fayalite. Crystalline phases and glassy matrix contain relevant amounts of zinc. The charge ore underwent only a mild roasting prior to smelting, as indicated by the relevant sulphur content. All the slags were obtained at temperatures ranging from 1150 °C to 1300 °C, using appropriate silica fluxes to optimise metal yield. Due to higher viscosity, massive matte may occur in the slags, with limited silver content. The Kutná Hora slags, when compared with previous studies from Italian smelting sites, show similarities in metallurgical techniques.