Onllwyn Colliery

Overview

Anthracite drifts at the head of the Dulais valley, developed by Evans and Bevan from the 1840s and connected to Neath by rail in 1864. The drifts closed in the 1960s but the washery outlived them by sixty years, taking opencast coal until 2023.

History

Onllwyn was developed from the 1840s by Evans and Bevan, and the mine was linked to Neath by rail in 1864. The workings were a collection of drifts in the upper Dulais valley taking the anthracite seams — the Big Vein, the Red Vein, the Peacock — and by 1913 the combined unit employed well over a thousand men. The official returns give anthracite throughout under Griffith Thomas and then Evans and Bevan, 227 employed in 1894 rising to 391 by 1905, and by 1940 there were 588 at No. 1 and 1,202 at No. 3. At nationalisation in 1947 Onllwyn went into the National Coal Board's South Western Division, No. 1 Swansea Area and later the new No. 9 Neath Area. It had its own coal preparation plant, a brickworks and the Area laboratory. No. 3 was closed by the Board in February 1962 and the No. 1 drift followed in April 1964. The washery outlasted the mines by a lifetime. Built in 1932 to serve the local drifts and re-equipped in 1950, by 1993 it was taking coal by road from the Nant Helen and Derlwyn opencast sites and putting out fourteen thousand tons a week, thirty per cent to the domestic anthracite market and seventy to industry, exporting through Swansea, Neath Abbey and Briton Ferry to Belgium, France and Norway — where one customer passed high voltage through the coal to two thousand degrees, drove off the volatiles and cast the carbon into refractory blocks for aluminium smelting. Celtic Energy bought the washery in 1995 and built a new plant around a heavy-media drum separator in 1998, capable of twenty-six thousand tonnes a week. It closed in 2023.

Geology

The anthracite belt at the north-western rim of the South Wales Coalfield, worked here through the Big Vein, the Red Vein, the Peacock, the Brass and the Nine Feet — the hardest and cleanest-burning coal in Britain.

Workings

A collection of drifts rather than shafts, Nos. 1 and 3 and the Brass Slant among them, driven into the anthracite seams of the upper Dulais valley and rail-connected to Neath from 1864. The colliery had its own washery, brickworks and, under the National Coal Board, the Area laboratory.

Closure

The National Coal Board closed Onllwyn No. 3 in February 1962 and the No. 1 drift in April 1964. The washery went on taking opencast coal until 2023.

What remains

The washery, the last architectural remnant of the local anthracite industry, closed in 2023 and has since been recorded by laser scanning and drone photogrammetry by researchers at Cardiff University's Welsh School of Architecture.

The washery buildings, disused since 2023, and the rail connection that served them.

Redevelopment

Coal preparation continued on the site until 2023, latterly for opencast coal from Nant Helen and Derlwyn.

Related mines

• Seven Sisters Colliery — Both were on the Dulais valley line, and Onllwyn's coal trains still ran through the site of Seven Sisters station long after either pit had closed.

Nearby mines

• Aberpergwm Colliery — 3.2 km E
• Seven Sisters Colliery — 3.5 km W
• Blaenant Colliery — 4.1 km S
• Yniscedwyn Colliery — 4.9 km W, Powys
• Rhigos Colliery — 6.0 km SE

Straight-line distance, within 15 km. Show on the map.

Recorded claims

Individual factual claims, each attached to the source(s) that support it below. Where sources disagree, both are kept.

• The Royal Commission's record, taken from a conversation with the site manager Frank Stagg in January 1993, says the washery was built in 1932 to service local drift mines, was substantially altered afterwards and re-equipped in 1950. By 1993 it served the Nant Helen and Derlwyn opencast sites, coal arriving by road, and produced fourteen thousand tonnes a week against an installed capacity of two hundred and fifty tons an hour. Thirty per cent went to the domestic anthracite market and seventy to industry for smokeless fuels, exported through Swansea, Neath Abbey and Briton Ferry. ¹
• A substantial part of the export went by rail to France and to Norway, where the customer calcined it: high voltage passed through the coal raised it to two thousand degrees and drove off the volatile material, and the carbon left was crushed, mixed with paste and cast into refractory blocks for furnaces, aluminium smelting among them. ¹
• The Durham Mining Museum's transcription of the Lists of Mines gives anthracite throughout, under Griffith Thomas and then Evans and Bevan and Evans and Bevan Ltd. Employment was 227 in 1894 and 391 by 1905; by 1940 there were 588 at No. 1 and 1,202 at No. 3, and at nationalisation the two produced 100,000 and 165,000 tons. ²
• Celtic Energy decided in 1998 to build a new coal preparation plant at Onllwyn capable of processing all its sites' production: a heavy-media drum separator for coal over twenty-two millimetres and heavy-media cyclones for the small coal, able to run twenty-four hours a day and take twenty-six thousand tonnes of raw production a week. ¹
• Tony Cooke's list, reproduced by Welsh Coal Mines, identifies the separate workings and dates them: Onllwyn No. 1, known as Dan Tai, from before 1831 to 1964; No. 2 Drift from 1916 to 1928, employing nine men; No. 3 Slant, previously Maesymarchog and Waen Marchog, from before 1831 to 1962; the Brass Slant from 1913 to 1933; the Trigloyn Slant from 1934 to 1962; the Nine Feet from 1936 to 1938; the Four Feet from 1937 to 1961; trial workings in the Eighteen Feet in 1927-28 and 1936-38; and Rhas from 1940 to 1953, working the Peacock and Bluers seams. Banwen itself dates from some point before about 1850. ³
• The 1923 list gives 193 employed at the Brass Slant producing from the Brass seam, 327 at No. 3 Slant working the Eighteen Feet and White seams, and 204 at No. 1 producing from the Nine Feet and Bleurs, with 137 surface workers across the colliery. The No. 2 drift was idle. ³
• Evans and Bevan of Neath still held the drifts in 1945 and employed over 1,200 men. The mine passed to the National Coal Board in 1947, and in 1955 Onllwyn No. 1 produced 114,475 tons with a workforce of 637. The South Wales Miners' Federation had a lodge here in 1926. ³

Photographs & further reading

Sources

1. (primary) Onllwyn Coal Washery — Processing and Distribution Centre (NPRN 306037) — Royal Commission on the Ancient and Historical Monuments of Wales
2. (secondary) Onllwyn Colliery — Durham Mining Museum
3. (secondary) Onllwyn — Welsh Coal Mines

Record created: 11 September 2026 · Last researched: 11 September 2026