Calcining Plant at Treskerby Mine

The calcining plant at Treskerby Mine is a late 19th-century structure built primarily of coursed granite blocks with galleting in the mortar. It features St Day brick dressings around the openings. The plant includes a labyrinth constructed from rubble, which also has similar brick dressings. The stack is made of coursed granite and has a stepped cornice leading to a St Day brick flue.

The calciner has a square plan and is located to the northeast of the labyrinth, with baffles connecting it to the stack to the southwest. It has segmental-arched openings on three sides, including an entry for ash removal on the northeast and a former furnace entrance with splayed sides for iron doors on the southeast. Inside, the walls are circular and encase a riddler sitting on squared walls above an ash box at a lower level. In the southwest corner, there is an opening for gases to exit into the labyrinth.

The labyrinth has lost its original brick roof, which was where gases condensed and arsenic was scraped off, although some springers from the originally segmental-vaulted ceiling remain. There are narrow round-arched access doors at regular intervals, a splayed opening for draught inlet at the northwest end, and slots for portcullis doors to control gases. Granite lintels are present over the final baffle area next to the stack.

Treskerby Mine was a significant producer of copper ore during the 18th and 19th centuries. This calcining plant is notable for its completeness as an example of this building type and likely represents a later re-use of the site, when copper burrows were re-crushed and calcined for arsenic.