FÁZOVÉ SLOŽENÍ STŘEDOVĚKÝCH STRUSEK PO TAVBĚ Pb-Ag RUD Z HUTNICKÉHO AREÁLU PLANDRY U JIHLAVY

Slags after silver smelting from the metallurgical site Plandry near Jihlava were examined in order to assess the conditions of smelting and composition of the charge. Samples were studied by a polarizing microscope in transmitted and refl ected light and selected phases were analyzed using electron microprobe. Two different types of slag were specifi ed on the basis of their phase composition. The first is made up of glass, olivine, and sulphides. In the second type, olivine and glass predominate and spinelide, K-Ba-feldspar, leucite, and sulphides are present in less quantity. Sulphides are present as droplets formed by the Cu-Fe-S matrix with inclusions of shandite, sphalerite, and an unknown Cu-Pb-S phase. Slag contains also relicts of unmelted quartz and chromspinel. The presence of Fe3+ in newly formed spinelide reflects at least partially oxic conditions during melting. The mesothermal type of ore with gangue formed by quartz, barite, and carbonate of the dolomite-ankerite series was probably processed. Low contents of lead in glass as well as low volume of Pb-Ag-bearing sulphides reflect good yield of metals of interest (Pb, Ag). Slags represent a potential environmental hazard due to relatively high contents of Zn (up to 6.6 wt. % ZnO in the glass).