Site Records


SiteName: Milwr Tunnel

Olwyn Goch Shaft
Rhydymwyn, Flintshire
OS Grid Ref: SJ201677

Sub Brit site visit August & November 1997

[Source: Cris Ebbs]

By 1938 the tunnel had reached the Pant-y-Mwyn Vein when low lead prices once again halted progress. All but 40 of the 650 men were made redundant and an era of great productivity drew to a close.

In 1939, Pilkingtons of St. Helens became interested in the high grade limestone of the mine for glass making and work began excavating large quantities of the stone, chiefly from the area to the west of Olwyn Goch shaft. Excepting the war years, this underground quarrying continued until 1969 and resulted in a series of impressive chambers, some up to 80 ft high, which if joined end to end would extend for 2 miles. Limestone output was 70,000 to 80,000 tons per annum.

Photo:The Limestone Caverns (note the person for scale)
Photo by Nick Catford

During the war twenty storage chambers were sub-let by Halkyn Mines to the Ministry of Supply for the storage of T.N.T. The chambers, each about 80 ft long by 30 ft wide were scattered throughout the workings, most being in the areas of Pen-y-Bryn Shaft, the Rhosesmor Branch Tunnel the Olwyn Goch Shaft and some at the level of the Halkyn Tunnel 200 feet above. The space for storage amounts to over 16,000 cubic yards. Each chamber was fitted with a timber floor and was protected from drips by the installation of corrugated iron "roofing". Although enormous quantities of T.N.T. were housed here, all chambers now lie empty apart from the concrete slabs that supported the timber flooring.


Great Hendre Lead Mining Company around 1911
Note headframe for Olwyn Goch (upper centre).
A jump in lead prices in 1948 prompted renewed activity at the main tunnel face and after a 10 year stoppage, it advanced south; lode 530 was discovered, which was rich in ore and provided work for 10 more years. Mid-way between Gwernaffield and Cadole during the 1950's the tunnel struck lode 524 on the Pant-y-Buarth Vein, followed by lode 501, both rich veins which were worked until the tunnel reached its present end in 1957 at the Cathole Vein just yards before the main Mold-Ruthin road.

This lode was unproductive at this point but a feeder brought in large volumes of sand and clay with water from cavities above although no connection was made with the old workings.

No lead was mined from 1958 to 1964 when work centred on the limestone mining at Hendre. A final jump in ore prices in 1964 kept the few men busy until 1977 removing ore from the existing lodes when the workforce never exceeded 40. Thereafter work revolved around maintenance and tunnel repairs until final closure in 1987.

The lead mines of Flintshire, since records were 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 an impressive 200,000 tons of lead ore and around 80,000 tons of zinc ore during its lifetime, the majority being extracted prior to 1957.

Photo:The Rhosesmor Branch Tunnel
Photo by Nick Catford

The Milwr tunnel today disgorges an average flow of 23 million gallons per day, rising to 36 million in wet weather. Two thirds of this water issues from two cave systems intersected by the workings. The chief source of one of the feeders was found in the Rhosesmor branch tunnel where Powell's Lode was intersected with a flow of 5000 gallons per minute coming from a flooded cave passage and in 1931 a natural chamber (Powell's Lode Cavern) was discovered.

Measuring 130 ft x 220 ft, it contains a lake to one side over 200 ft deep. Adding to this depth the height above water level of 150 ft indicated on mine plans, it can claim to be the highest natural underground chamber in Britain. In order to mine below sea level in this area a shaft was driven to a depth of 128 feet where pumps were installed capable of handling 14000 gallons per minute, the largest mine pumping complex in the UK. The lake was lowered by 120 feet but has now risen back to the level of the Rhosemor branch tunnel.

Photo:Powell's Lode Cavern - The 'Tippler' was used for tipping waste rock into the lake for 6 years without affecting water levels.
Photo by Nick Catford

Rolling stock during the 1930's consisted of one diesel locomotive, one tandem battery loco, two single battery locos, 360 mine cars of 18 cu ft capacity and a number of passenger cars known as man-riders. The double bogie diesel loco, first introduced in 1933, weighed 7.5 tons and was capable of hauling 60 loaded cars. The tandem battery loco comprised two separate units connected by jump leads and a swivel coupling. The combined unit weighed 5 tons and was capable of hauling 50 loaded cars. The remaining battery locos each weighed 2.25 tons and were rated at 6 m.p.h. Three hundred and ten of the mine cars were end-tippers and the other 50 were box cars. Each car was numbered, a record kept of each service or repair and servicing was carried out at a workshop at tunnel level beside Olwyn Goch Shaft. The track gauge used throughout was 22.5 inches

Further information and pictures about this site continues here

[Source: Cris Ebbs]

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