Interesting info Roy.
The photo I have in mind is on P71 of Mining in Cornwall V4. (Bullen)
It shows the comedy weeny headgear over the shaft.
I suppose it's a case in point about how reworking is "more mining" and obliterates the last layer of history in some cases.
Another prominent loss were the bunch of engine houses on Penhale Point, knocked down as they were a landmark (potential) for a WWII attack.
Looking at the 1888 maps of Cornwall, just goes to show what a huge amount of stuff went missing between then and the subsequent 1909 edition. It's just the way the ball rolls onwards.
At a risk of sounding like my dad, I suppose that we will see the gradual overgrowing of workings like Consols, S Caradon, Wheal Busy, until the landscape is unrecognisable. Talking of which, Bullen's book has a photo of Killifreth back in the day when it looks more like the photos from a mars landing. Fantastic series of books and well worth a thumb through....