MINERALOGY OF MEDIEVAL SLAGS FROM LEAD AND SILVER SMELTING (BOHUTÍN, PŘÍBRAM DISTRICT, CZECH REPUBLIC): TOWARDS ESTIMATION OF HISTORICAL SMELTING CONDITIONS*

Slags from the Pb/Ag medieval (14th century) smelting plant located at Bohutin, Přibram district, Czech Republic, were studied from the mineralogical and geochemical points of view. Two types of slags were distinguished: (i) quenched slags formed mainly by Pb-rich glass and unmelted residual grains of SiO2 and feldspars, and (ii) crystallized slags mainly composed of Fe-rich olivine (fayalite) and glass. The mean log viscosity value of the slags calculated for 1200°C was 2.119 Pa s. The morphology of olivine crystals was used to estimate the cooling rates of the melt, for some slags indicating rates > 1450°C/h. The projection of the bulk composition of slags onto the SiO2–PbO–FeO ternary system was used for rough temperature estimates of slag formation, lying probably between 800 and 1200°C.