The results of studies of slag from the excavations of the medieval settlements of Novy Bor I, III, IV (the Ust-Tsilemsky District of the Komi Republic) are presented. Analytical investigations were conducted using optical and scanning electron microscopes, X-ray diffraction, and spectroscopic techniques. Mineralogical and chemical analyses revealed slags indicative of both ferrous and non-ferrous metallurgical activities. Slags from ferrous metallurgy were primarily composed of siliceous iron-rich materials, with additional elements such as aluminum, calcium, phosphorus, and potassium. Microprobe analyses confirmed the presence of minerals like fayalite, wüstite, iron-silicate glass, and reduced iron. Non-ferrous metallurgy slags exhibited a composition characterized by siliceous-calcium-aluminum phases, alongside elements such as iron, phosphorus, sodium, and potassium. Identified minerals included fayalite, wüstite, wollastonite, plagioclase feldspars, iron-silicate glass, magnetite, and copper-iron inclusions. Smelting temperatures for iron oxide ores ranged between 1000 and 1400 °C, while copper oxide ores were smelted at higher temperatures up to 1600 °C.