Cerva: wolfram mine

Wolfram a vital mineral during WW2 and a tool for Portuguese neutrality through commerce with both parties.
The mine of Cerva at the North of Portugal {Vila Real] is now abandoned. But it was [see here, here and here for more] the source for tungsten and quartz. 
The mine was explored by Sociéte Civile d'Études de Tous Gisemants Miniers (Paris), after 1945 Companhia Portuguesa de Minas - Concessão de S. João de Escourêda; and after 1956 Minas de Cerva SARL.

Photo source: jab