Reasons for Designation
Cornwall and West Devon, has been one of the major areas of non-ferrous metal mining in England. It is defined here as prospecting, extraction, ore processing and primary smelting/refining, and its more important and prolific products include copper, tin and arsenic, along with a range of other materials which occur in the same ore bodies. The 18th century saw technological advances turning to the mining operations. During this period, Cornish-mined copper dominated the market, although it was by then sent out of the region for smelting. The development of steam power for pumping, winding and ore processing in the earlier 19th century saw a rapid increase in scale and depth of mine shafts. As the shallower copper-bearing ores became exhausted, so the mid to late 19th century saw the flourish of tin mining operations, resulting in the characteristic West Cornish mining complex of engine houses and associated structures which is so clearly identifiable around the world. Ore processing increased in scale, resulting in extensive dressing floors and mills by late in the 19th century. Technological innovation is especially characteristic of both mining and processing towards the end of the century. Arsenic extraction also evolved rapidly during the 19th century, adding a further range of distinctive processing and refining components at some mines; the South West became the world's main producer in the late 19th century. From the 1860s, the South West mining industries began to decline due to competition with cheaper sources of copper and tin ore from overseas, leading to a major economic collapse and widespread mine closures in the 1880s, although limited ore-extraction and spoil reprocessing continued into the 20th century. The part of the mining complex of Wheal Basset and Grylls Mine called Tyack's Shaft survives well, following consolidation of the building, and bears witness to a tragic accident within this important and dangerous industry. It formed part of a productive and long-running mine.
The monument includes part of the mining complex of Wheal Basset and Grylls Mine, situated to the south of the settlement of Porkellis. The complex survives as a beam engine house with an attached chimney beside the shaft called Tyack's Shaft. The engine house is small and rectangular in plan. It stands to full height and is roofless, built of granite and brick. There is a round-arched brick-built door to the rear and flat granite-lintel windows elsewhere. The circular chimney tapers upwards and is granite-built at the base with brick upper sections. The engine house was built in 1858 to house a 60 inch cylinder pumping engine. More recently the fabric has been consolidated.
The Basset and Grylls Mine was first documented in 1574 as Redde Worke, later known as the Ball Reeth, Porkellis United and New Porkellis. The main production era was from 1858 to 1913 and the mine is documented as having produced over 4,650 tons of black tin. The last phase of re-working was in 1930. In 1858 the worst mining accident in the district befell the mine when seven miners were killed when a surface pond of tin 'slimes' collapsed and flooded the mine workings. The engine house and Tyack's Shaft were constructed as a result of this accident.
The engine house stands within the World Heritage Site 17, the Cornwall and West Devon mining landscape.
PastScape Monument No:-1472352 and 425958