The copper and tin ores mined from Levant were relatively complex and their treatment (as with other mines in Cornwall) put the Cornish extractive technology at the forefront of development during the nineteenth and twentieth centuries.

In the preceding centuries the alluvial stanniferous material had been metallurgically simple to recover and smelt, but as the mines went underground the primary ore became more complex with tin and copper ores occurring together.

Copper ores were found as green secondary minerals or grey sulphides that were separated by Bal Maidens with spalling hammers and other simple techniques. The lower grade ores were crushed by stamps which reduced the ore to a sandy powder. This resulted in a complex concentrate of tin oxide, copper sulphides, iron sulphide, and arsenic sulphide after treatment with water in buddles.

The mixed concentrate was then calcined (roasted) in a coal fired rotary furnace. As time went by the technology was improved but the Brunton horizontal calciner was well known up to the 1930's.

This calciner had the effect of reducing the copper sulphides to copper oxides with the evolution of sulphur dioxide and the accessory arsenic sulphide to arsenic oxide (a substance that has the ability to sublime i.e. go from solid to gas and back again). Thus after calcination the arsenic had been removed and the copper sulphides reduced to copper oxide. The arsenic was recovered by condensation in arsenic flues (passageways) where the gaseous arsenic oxide sublimed to solid arsenic oxide, with the appearance of thick white powder. In effect this was a deadly white soot which could be injurious to the health of the workers those job it was to shovel it off the flue walls.

The mixed tin and copper oxides were removed from the calciners and allowed to cool. Remnant sulphur combined with oxygen in the atmosphere to form sulphuric acid which dissolved the copper oxide to form copper sulphate. The addition of water took the copper sulphate in to a blue solution which could be separated from the unaffected tin oxide (cassiterite). Any iron oxide was converted to ferrous sulphate and could be removed from the tin.

By now the tin was relatively pure and could be dried and sold to the smelter. The blue green solution of copper/iron sulphate could be removed and treated. Copper sulphate solution when in contact with metallic iron reacts o form copper metal and iron sulphate - a useful reaction! This is known as cementation. Thus a tank full of scrap iron, when flooded with a solution of copper sulphate reacts to reduce the copper sulphate to copper metal slime and iron sulphate.

Levant thus sold tin oxide, copper sulphide ore, copper metal slime, and arsenic oxide.

Thanks to Charles Smith (ex Geevor geologist) for this article.