Ball Mill

A single ball mill stands in the milling area at Ashio Copper Mine, its cylindrical drum mounted between two steel pedestals. The drum is gear-driven, the large external ring gear still meshed with its drive pinion. The fabrication is from an earlier era of heavy machinery. The steel plates are joined with rows of hand-driven rivets, hundreds of them visible on the side facing the camera. The drum is stained with ore residue. The gears, still oiled at some point in their working life, are now dark with fixed grease and rust. A scaffold at the right of the frame shows where workers used to climb to load balls into the drum.

Ball mills like this one pulverised the rock that came up from the mine into a powder fine enough for the flotation process. The rotating drum tumbled steel balls against the ore until it was reduced to grit. Ashio ran its mills almost continuously for decades. The hand-riveted construction puts this drum at well over a century old, predating welded-steel fabrication that became standard from the 1930s on. The mill never operated again after the mine closed in 1973. The gears are still in place because nobody has had reason to remove them.