Medieval barium-rich slags after melting of polymetallic ores from selected sites in Jihlava

Vol.20,No.1-2(2013)

Jaroslav Kapusta Zdeněk Dolníček Karel Malý

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Abstract
The studied slags originating from western part of town of Jihlava are predominantly composed of glass and unmelted corroded grains of quartz. Newly formed phases (barium-rich feldspars and sulphide inclusions) are only accessoric. Feldspar contains up to 72 mol. % of celsiane component. Sulphides form droplets (typically X0 μm, rarely bigger than 0.5 mm) composed of pyrrhotite and sphalerite. Bulk slags show elevated heavy metals, especially Pb (up to 0,35 wt. %) and Zn (up to 1.35 wt. %), however, these values are significantly lower than in case of other published localities. The presence of high content of Ba in bulk slag, which is always higher than 5 wt. % BaO, is unique. The WDX analyses of glass showed up to 23.3 wt. % BaO and strongly heterogeneous distribution of Ba. Viscosity index v.i. and dynamic viscosity log η were calculated from bulk chemistry. The calculated values appear to be overestimated due to unusual chemical composition. It would lead to ineffective smelting procedure and/or necessity of very high temperatures. To compare obtained values with reality the melting experiments in an electric oven were realized. Maximum achievable temperature of 1 100 °C led to a complete melting of all samples except the quartz-rich one.

Keywords:
Jihlava Ore District; slags; polymetallic ores; heavy metals; barium
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