National Geographic : 1940 Nov
Tin, the Cinderella Metal 665 Photograph from Alicia O'Reardon Overbeck Bolivian Prospectors Drill for Tin with Burro Power The metal occurs chiefly in veins, but sometimes in placers, deposits where the tin may be washed out with hydraulic equipment (page 670). The burro turns a drill, weighted down by the men. The drill brings up samples to determine whether the percentage of tin is high enough to make placer operations profitable. Photograph by James C. Sawders Down Comes the Empty Ore Car, Ready for Another Burden of Tin Some of the shafts here in the Llallagua mine at Catavi, Bolivia, are 1,000 feet deep (page 664).