Refinery

The refinery at Ashio Copper Mine occupies one of the lower levels of the processing plant, where the copper concentrate from the flotation circuit was treated to produce the final copper product. The refinery floor is a long open hall, with the lines of treatment vessels and furnaces set along the centre. Heavy structural steelwork frames the roof above. Brick-lined furnace chambers are visible at one end of the hall, their flue ducts running up through the ceiling toward the stack outside. Cooling lines and pipework run along the walls. The floor is concrete, stained with the metallic-grey residues of copper-refining process. The light here is low; the upper windows are partly bricked in to control the working temperature inside.

The refinery is where Ashio's copper concentrate became the saleable product that went down the valley by rail. The exact metallurgical processes used at the site changed across the plant's operational decades, from earlier pyrometallurgical methods to later refining circuits introduced during the Furukawa modernisations. The plant operated from 1877 onwards. The Excavation Department closed in 1973. The refinery shut at the same time. Some of the higher-value plant has been disturbed in the years since; the structural elements, the furnace chambers, and the heavier vessels are essentially as they were left.