Mining – metallurgical activity has been taking place in Mežiška dolina valley for more than 300 years. The activity originates in 16th century. In the beginning the process of lead extraction was simple. Rich galena ore was processed exactly where it was dug out. It was heated with firewood, air was conducted into mixture and by this sulphur burned up. Metal lead, gas and non-reactivated residue were extracted. Throughout the years processing technology has changed from 'Koroška' furnace in 16th century, through 'Kompš' and 'Pirker' furnace at the end of 19th century, to roasting machine, shaft-like furnace for lead (high furnace) and rotary furnace. Mining and smeltery activity took place from Koprivna (Pečnikova žaga) to Mežica (Polena). One of last smelteries which were operating outside Žerjav was on Polena (1834 – 1906). After 1897 this activity has been performed in Žerjav.