Cefn Coed Colliery was opened as an
anthracite colliery by the Llwynonn Colliery Company during the 1920s. Three attempts were unsuccessfully made to sink shafts at Cefn Coed, but it was not until the Llwynonn Colliery company was bought out by the Amalgamated Anthracite Combine of
Ammanford in 1926 and high capital investment made, that a break was made in the hard Blue Pennant
sandstone. The first
coal raised in 1930, with the shaft and workings powered by a steam engine, fueled by the gas from the old workings. Like much of western
South Wales coalfield, the coal was high quality
anthracite. The best coal came from the deepest seam called Big Vein, broken into at a depth of 750 yards. Cefn Coed during its working life at depths of over 2,500 feet (800m), was the deepest anthracite mine in the world. Other seams worked at Cefn Coed included: Peacock, White Four Feet and the Nine Feet.
Brammallite was identified in the Dulais seam, by
X-ray diffraction by the
Natural History Museum,
London; making Cefn Coed one of only two sites in all of Wales for Brammallite. However, at such depths and with frequent
mining accidents due to
methane gas and roof falls, the pit and it soon gained the unenviable
nickname of "The Slaughterhouse." By the end of
World War II in 1945 there were 908 men employed. Nationalised by the
National Coal Board, continual investment was required to combat the need to keep roadways open at the extreme depths. Changing economics lead to a reduction in the workforce from the 1950s, and the mine ceased production in 1968. A majority of the men were transferred to the new Blaenant
drift mine, built to extract coal form the No.2
Rhondda seam at a shallower depth. One of the two shafts at Cefn Coed was used to ventilate Blaenant, and as an emergency exit, until the closure of Blaenant in 1990. ==Museum==