As Neil says almost all of the physical evidence of the mining heritage has gone. There is very little left of pit heads and associated buildings themselves. Don't forget the Stadium of Light is built on the site of Monkwearmouth Colliery, one of the last to close. If anything is left it is mostly the pit wheels which have been made into memorials in many pit villages. Old shafts have been sealed and all that is left are small chimney like structures which, I understand, are part of environmental monitoring systems.
Unless, of course, the strategic reserve is down there rather than in Box tunnel.