Greenfield represents a linear water-powered industrial valley rather than a single mine site, extending approximately 1½ miles from Holywell town to the Dee estuary.
The valley contains the remains of an integrated sequence of water-powered industrial sites including mill foundations, wheelpits, masonry platforms, reservoirs, leats and tailraces associated with copper rolling, brass battery working, lead processing and later zinc smelting and chemical manufacture. These works were powered by a closely managed sequence of reservoirs and leats derived from the Holywell Stream. The valley functioned as the principal processing and export corridor for ores from the Holywell leadfield, with finished products shipped via Greenfield Dock on the Dee estuary.
Industrial use of the Greenfield valley began in the medieval period when the monks of Basingwerk Abbey first exploited the Holywell Stream for milling and wool processing. By the later 16th century the valley had become established as a location for water-powered industry connected with the growing Holywell lead-mining district.
During the 17th and especially 18th centuries Greenfield developed into one of the principal metallurgical processing centres serving the Holywell–Halkyn leadfield. Lead from nearby mines was smelted and refined in the valley, while copper ore imported largely from Parys Mountain was rolled and manufactured into sheet and finished goods.
By the later 18th century a dense concentration of water-powered industrial sites occupied the valley floor. The Meadow Mill rolling works (1787) formed part of the industrial network associated with Thomas Williams and his Anglesey copper enterprises. In 1842 a large zinc smelting works was constructed near the lower end of the valley by William Crockford.
Industrial activity continued through the 19th century with paper manufacture, chemical works and textile production, before gradual decline during the early–mid 20th century. A rough timeline of industries includes:
- brass and copper battery works (1766–1802)
- copper rolling mills (18th–19th centuries)
- Meadow Mill rolling works (from 1787)
- cotton mills (late 18th century)
- zinc smelting works (from 1842)
- paper mills (from c.1770)
- chemical and later rayon-related industry (20th century)
Much of the former industrial area now lies within Greenfield Valley Heritage Park, which is open to the public as a country park and industrial heritage landscape. Public access is generally good along valley footpaths, former railway alignments, reservoir margins and preserved mill sites. Some structures survive as standing ruins, but access to interiors is limited or restricted. Individual remains outside the heritage-park boundary may lie on private land.
The central mill complex at Greenfield is protected as the Greenfield Valley Mills Scheduled Monument (Cadw ref. FL160). The designation covers the remains of:
- brass and copper battery works (1766–1802)
- rolling mills (1823–1898)
- Meadow Mill rolling works (1787–1860s)
- cotton mill complex (1785–1840)
The monument is considered of national importance for its contribution to understanding early industrial water-powered manufacturing processes and retains significant archaeological potential. Additional remains elsewhere within the valley form part of the wider historic industrial landscape, portions of which are also scheduled. Disturbance of scheduled areas requires Scheduled Monument Consent.
