I made a temporary web page with links to three J. van Laun photos of the powder house here: http://www.dchopkins.co.uk/misc.htm. Also there's a composite of 2011 and 1978 photos to compare the stone arrangement in the wall. The copies of the 1978 photos were taken (with permission) on my camera, so they're not the best quality.
I didn't find new information/photos on Hill Pits at Pontypool Museum. The librarian suggested that the colliery owner was the most likely to have taken photos, but they don't seem to be with the Blaenavon Company records deposited in Gwent Records Office, which Mike has searched.
Keeping on looking,