Trust Regional Historic Environment Record
Precipitation Tanks, Parys Mountain
Primary Reference Number (PRN) : 3498 Trust : Gwynedd Community : Amlwch Unitary authority : Ynys Mon NGR : SH44609045 Site Type (preferred type first) : POST MEDIEVAL PRECIPITATION PITS Status : Scheduled Monument
Description : For obtaining copper by precipitation from water drawn from the mine. The precipitation pits are probably C19th. <1>
Richer copper than that produced from the ore was obtained by precipitation from the water which accumulated at the bottom of the great hole where mining took place. This method was practised at Parys Mountain from the early days following the discovery of copper. The strength of the water is appreciated when it is realised that a key dipped in the precipitate ponds became covered with copper in three seconds. The water itself was worth 1 1/2d a quart at the end of the C18th.
As early as 1772 and 1773, when mining was still in its infancy at Amlwch, considerable quantities of iron for use in the precipitation ponds were being brought from as far afield as London. The water which was saturated with sulphate of copper was drawn up from the mine in buckets raised by whimseys. It was then transferred into specially prepared ponds about 36ft long, 15ft wide and 18 to 22ins deep. Large quantities of iron were placed in the ponds and left there for the natural action to take place. The iron was regularly turned until it finally dissolved, leaving copper precipiate mixed with the mud at the bottom of the tank. This contained 20-30% copper. <3>
An extensive copper and ochre precipitation system which occupies a natural gulley in the eastern half of the mountain. The large ochre pit at the lower end of the system has been largely obscured by tailings, but the copper precipitation pits themselves survive largely intact. The argiau consist of low stone walls enclosing precipitate and other finer material. The system is fed from three points; a tunnel, a row of pillars, and an adit emerging from underneath the road.
There are approximately twelve pits at the site, making it a much smaller site than that of Henwaith, with ancillary structures to the north which may well be precipitate drying rooms and a furnace. The pits are constructed of stone blocks, and in places the retaining walls are constructed of cut stone blocks of the same dimensions of those used in the base construction. They are mortared and as much as four courses high in places. The stone block bases of the pits are very well preserved, and exhibit chequering in the stone work indicating the location of the built troughs. Unlike the Henwaith site, there is no water or residue to obscure the bases of the pits or the site in general.
The Hillside site has been marginally affected by the influx of heather, especially on the argiau. However, the site itself is in excellent condition, with intact culverts and impressive wooden sluice gate remains. Indeed, a brick-built arch in the western embankment wall has an excellently preserved wooden sluice gate in situ. The ancillary structures are moderately well preserved, with much less debris than the Henwaith site, and with walls up to 2.0m in places. The central northern structure is in a state of excellent preservation, with walls up to 4.0m high, as well as clear evidence of windows and door openings. <6>
A collapsed shaft: the depression is 12m in diameter and is blocked by stone 3m, below the present ground surface. There are traces of a stone shaft-collar. (Gwyn, 1998)