The network of mines, lodes, shafts and natural cave systems extends more than 60 miles under the Flintshire and Denbighshire countryside – and it’s a rare sight to see
Beneath a vast area of North Wales lies a hidden world unknown to many. A labyrinth of mines, veins, shafts and natural cave systems stretches over 60 miles beneath the Flintshire and Denbighshire countryside.
The Halkyn District United Mines boasts the longest traditional passage-based mine network in the UK and Ireland. At its core is the Milwr Tunnel, a mine drainage adit extending some 10 miles, from Bagillt on the Dee Estuary to Cadole near Loggerheads, Denbighshire.
It paved the way for further exploration by draining water from the mines. At its peak, the network of lead, limestone and zinc mines employed 650 people, but this number dwindled over time until the mines were eventually shut down in 1987.
Today, the adit – managed by United Utilities – releases millions of gallons of water into the Dee Estuary daily. This water was once utilised by mills located near the coast, reports North Wales Live.
Access to the complex is rare, with only caving clubs permitted to organise visits. Edward Coghlan, who last ventured into the network in 2024, shared images from inside with North Wales Live.
Cris Ebbs, author of The Milwr Tunnel: Bagillt to Loggerheads, 1897-1987, detailed its central role in the local mining industry on extensive pages about Flintshire lead mining, hosted by www.cambrianmines.co.uk..
He explained: “It successfully drained over 50 veins and created a labyrinth of over 60 miles of interconnected passageways.
“At a time when low ore prices were crippling the industry nationally, the working of new and existing ore deposits during the 1930’s ensured that up to 650 men were employed by the mine and tunnelling records were being broken.”
He further added: “The Milwr Tunnel was begun in July 1897 from a point 9 feet below high water mark at Boot End near Bagillt by the Holywell-Halkyn Mining and Tunnel Company.
“The tunnel gradient is 1:1000 throughout and the fastest rate of tunnelling was 54 feet a week. The tunnel walls are brick lined for 1.5 miles where the tunnel passes through shale and coal measures, but thereafter is in chert or limestone and is generally self-supporting.”
As the drainage tunnel – which had rail tracks laid on it for transporting people and goods – advanced, veins were cut off the main route. Lead and limestone were the primary materials mined.
Limestone went to Pilkington’s of St Helens for glass making and was also used for agriculture and as an ingredient in toothpaste. Ore was shipped to Avonmouth or Chester for smelting.
In his research, Chris stated: “At the intersection of the Pant Lode, a flooded cavern, known locally as a loch or vugh, was cut at 6am on 5th January 1917. This caused St Winefride’s Well at Holywell, 2.5 miles to the north, to run dry 11 hours later.
“The burst of water swept loaded trucks along the tunnel until they jammed and sand blocked the tunnel, being two feet deep at the entrance, seriously hampering progress for many weeks. Water levels in a number of neighbouring mines were also affected.”
Despite this hiccup, production continued unabated for several decades. He further noted: “The lead mines of Flintshire, since records were first kept in 1845 up to the first world war, produced a total of 400,000 tons of lead ore and over 100,000 tons of zinc ore.
“Since then, the Milwr Tunnel and associated lodes have produced a further 200,000 tons of lead ore and around 80,000 tons of zinc ore, the majority of this being extracted prior to 1957.”
Limestone production clocked in at an impressive 70,000 to 80,000 tons annually, resulting in the creation of awe-inspiring chambers, some towering to 80ft high. Since the 1990s, mining enthusiasts have brokered access agreements, leading to exploration of many of the old mines and caverns.
Permission was granted to reopen two old shafts as emergency exits, and provisions were made for an emergency phone line and rations.
Local caving clubs offer tours to members from other clubs, providing a sneak peek into this subterranean world before returning to the surface.
#Incredible #underground #labyrinth #runs #miles #beneath #North #Wales
