Since in 1851 Abraham is clearly located in West Dean (but in Monmouth district for Census purposes) I assume that what is meant is the Old Sling Pit iron ore mine. The BNA tells us this was put up for auction in 1851 when its location was given as Clay Lane End, Clearwell Meend. This was a productive area for iron ore and a number of pits are marked on the following map (but not that particular one). In 1861 Abraham’s location is actually given as Clearwell Meend.

http://maps.nls.uk/view/102346004

There are a few historical details here for starters and I guess there will be rather more than that if you search the net,

http://www.british-history.ac.uk/vch/glos/vol5/pp326-354

Have you tried searching the Forum? I’m sure it will have been mentioned before.