Penallta Colliery © Janice Lane. The last deep mine in the Rhymney Valley, closed in 1992. At its peak the colliery employed over 3,000 men in a number of adjacent communities and at one time held the European record for coal production. It had been at the heart of the local economy and the local community for over 85 years. The closure of the colliery had a major impact in terms of the social, economic and environmental needs of the area.