Columbia subject headings:
Harvard subject headings:
Tin
Tin mines and mining--Portugal--Viseu.
Tungsten mines and mining--Portugal--Viseu.
Tungsten ores--Portugal--Viseu.
Princeton subject headings:
Tin mines and mining--Portugal--Viseu--History--20th century.
Tungsten mines and mining--Portugal--Viseu--History--20th century.
Viseu (Portugal)--Economic conditions--20th century.