Pete,
Interesting about Trebarwith area quarries. A few pointers if you're in the area.
Inland from Trebarwith, Prince of Wales quarry has a nice winding engine. There are mine workings at Tregardock Beach. Barratts Zawn has a collapsed tunnel. Not sure if it's metal or stone. Haven't been around Port Issac myself but there are extensive mines there. I'd say that T'Dock and BZ are next ports of call.
Your shot of trebarwith strand beach (funnily enough, welsh coal was dumped from barges at high tide and collected at low-you can still find it) shows a major collapse on the far headland (near colours cove) which is recent.
Interesting about Backways Cove, apparently it has a notable ghost (if you believe that rubbish).
If you walk from T Strand to Tintagel, there are more cliff workings and the rock becomes more consolidated. T Strand itself has extensive pillow lavas.
I also think there are unrecorded trials in the Bossiney area.
I spent a lot of time in the area looking for places to surf and Trebarwith is one of my favourite emmet free beaches in Kern.
Hope this is interesting...... Stu