Boscaswell United mine started during the tin boom of the early 20th century, first appearing in May 1906 when North Boscaswell Mine was floated with a capital of £10,000. By September the mine had a winding engine installed and the new Trease shaft was 84 feet deep. The lode was over 2 foot 6 inches wide and assayed 43 lbs of black tin per ton.
1907 the company was called Boscaswell United Tin & Copper Mines, Ltd and the property included the setts of North Boscaswell, Pendeen Consols, Trease, Calartha Farm, Boscaswell Downs, Calartha Common and Portheras. Douglas S. S. Steuart was the managing director and Pore, Petit and Steuart the consulting engineers. The day-to-day management was handled by Willie Thomas who was also managing Botallack; he was the local agent for Steuart.
1908 Trease Shaft was sunk 190 feet, the lode at 180 feet reported as carrying 24.7% copper and 71.2 lbs per ton black tin. By the end of the year the shaft was down 282 feet and a level driven 322 feet east.
1909 Douglas Steuart acquired the surface plant of Worvas Downs and South Providence mines near St Ives. The equipment included a 20-head Californian stamp battery and some Frue vanners. Later the mill would include quite exotic equipment in the form of Pinder tables (circular rotating shaking tables also called Sturtevant concentrators) and a Merton roasting furnace. Another shaft, Treweeks, was sunk at some point. This shaft is located to the north-west of Trease Shaft, close to the mill.
1910 to 1922 Boscaswell United mine appears to have been working on and off through this period.
1911-12: Production quoted as 23.7 tons black tin (Burt et al)
1918 ownership of the property had been transferred to Home Minerals Ltd, which also owned Carnelloe Mine near Zennor and Silver Valley near Liskeard. In the three months to December 1918 the mine had sold 6.3 tons of black tin worth £1,060. The mine was still being worked in 1919; it is not known when it closed.
Trefvithick Society Boscaswell United
St Just Area Mines, Cornwall