The Watergate Smelt Mill, which stood a quarter of a mile (0.4 km) south of Castleside crossroads, [National Grid Ref. NZ 078484] was built around 1803 to smelt lead ore from the Healeyfield mine. In 1821 it had 1 roasting furnace, 2 ore hearths, 1 refining furnace and 1 reducing furnace and was owned by The Healey Field Mine Co.
Parsons and White’s Directory (1828) states that a large quantity of ore from Muggleswick parish was smelted in a mill near Healeyfield belonging to Thomas F. Featherstone and Co. of Newcastle which had an annual production of 2,000 ‘bings’ of lead and some silver (1 bing = 8cwt.). Fairbairn considers that this should in fact be ‘pieces’. When the Stanhope and Tyne Railway opened in 1834, lead ore was brought for smelting from other mines further a field. On July the 3rd 1849 the mill was advertised for sale by auction.
The mill had a tall, square chimney constructed in red brick and a large, complex, horizontal flue system. The fumes emitted by lead smelt mills were highly poisonous. As well as sulphur dioxide, they contained residues of lead, which vaporised and emerged with smoke. As early as 1778, Bishop Watson in his Chemical Essays pointed out that this loss of lead was uneconomic and suggested the introduction of horizontal chimneys of sufficient length to condense the lead fumes. The lead, and also silver, residues could then be collected from the walls of the chimney. This recovery, often carried out by young boys, was a dangerous and dirty job as there were poisonous substances present in the residues.
By 1923 the mill was in the hands of John Walton & Co. and had ceased to smelt lead in1913 although it continued to smelt lead residue for a time after this date. It then stood idle until 1939, when it was purchased by Platt Metals Ltd whose business was the recovery of non-ferrous metals from scrap cables. This involved burning off rubber coating from the cables and the fumes produced by this process led to protests from local residents. As a result, the mill finally closed and the plant was dismantled and taken to the firm’s main factory at Enfield. The tall mill chimney developed a ‘bend’ around the middle, which worsened, leading to its eventual collapse. All of the mill buildings have since been demolished but some remains of the horizontal flue system can still be seen curving up the hillside above the car parking area which has been created on the site.