history mining engineering 90 ore deposits 26 silver 17 uranium 13 ores 10 deep mining 9 more ... metallography 8 lead 6 brown coal 5 hard coal 5 deposits mining 4 geological survey 4 mineral deposits 4 gold 4 workings 3 heraldry 3 mining law 3 caustobiolite deposits 3 mining 3 coal 3 mineral processing 3 non-ferrous metals (geology) 2 tin 2 mines (mining) 2 mine rescue 2 non-ferrous metallurgy 2 museums 2 environment protection 2 landscape recultivation 2 less ...