Well done in getting out there to photograph the remains. Tried a few years ago, but the low tide wasn't low enough :(
If you haven't got a copy it is well worth tracking down Peter Joseph's "So very Foolish (A History of the Wherry Mine)" published by the Trevithick Society, 2012 (ISBN: 978 0 904040 95 1).
It is a fascinating history, but as an A5 booklet, items like this tend to "disappear" quite quickly.