I know that one well, it's the Tapistone vein and the fenced-off shaft in the woods just below the choked one in the field is Tapistone Tongue Mine. The Orpheus had a look at it in the 1970s but had a lot of problems with instability that led them to call it "Death Hill Shaft"- the roll of steel sheet is what they were using to try and keep the shaft top together after the ginging heeded the call of gravity. There's an adit lower down the hill but it's massively run in, hence I've never bothered asking the National Trust about digging it out.