Dave,
a useful resource for you would be the Durham Mining Museum, available online. I know that the Ouston and Urpeth pits are on there, (I live there). Pelton Library has a few books in the local interest section that you might find useful. Also the National Library of Scotland have a very useful resource of old OS maps available online.
I am a bit busy for the next week or two, but have been walking the area for the past 30 years and have an idea about some of the pits, if you PM me with your email I may be able to offer a few more pointers.
Colin