Daw Mill Colliery in Warwickshire is the UK's largest extant coal mine, employing 800 workers in a five meter high seem reached by two pit shafts, 556 m and 558 m deep, respectively. It holds the record for the most coal produced by a UK mine in a single year, 3 million tonnes in 2008, and is thought to have sufficient reserves for another ten years of production. Despite this UK Coal, the company that owns the mine, has struggled to remain financially viable in recent years, with the Financial Times giving a figure of £139 million in debts, and losses in 2010 of £125.1 million on a turnover of £351.2 million.
Section of the Daw Mill Colliery, from a 1981 publicity brochure.
In December 2011 workers at the Colliery ran into an unexpected geological fault, causing production to drop sharply. The Union of Democratic Mineworkers, which represents the majority of miners at Daw Mill has already agreed a 10% pay cut for workers till the situation is resolved, and a two year pay freeze, but was informed this week there was a strong possibility of the mine closing as early as 2014.
Geological faults are areas where rock strata are broken by movement in the Earth. This is most commonly associated with Earthquakes in the popular imagination, but is a serious problem for mining operations, particularly subsurface ones, as miners reaching a fault can find the layer or rock they were following (in this case a coal seem) simply vanishes, and will need to be found again before excavation can resume.
Faults occur when rock strata are split and move past each other. This is not always visible at the surface, particularly in ancient faults that may have been covered by subsequent deposition. National Earth Science Teachers Association/United States Geological Survey.
Daw Mill has also been in trouble for safety reasons in recent years, with three miners killed in 2006-7, and a £1.2 million fine for breaches in health and safety regulations in 2011.