It's mentioned in Bick, my copy of which appears to have made it's way to work. There is what appears to be an adit by the river, although for whatever reason I've never hopped down to see if it 'goes', and some pits presumably along the lode. The most obvious feature is the sublimation flue. There's quite a few interesting little things in the vicinity, including a molybdenum 'mine' and a mine buried under Penrhyn waste.
Robin