I came across this site when travelling into Cornwall with a friend for a short holiday in 1997. We were amazed to see the bright turquoise colour of the water and the huge white heaps on an unearthly landscape, so we went to investigate. It's situated just outside the town of St Austell, and is not too far from the Eden Project, which was created in another, albeit disused, clay pit. There are several of them in this area.
China clay (Kaolin) is found near to granite layers, much of which is in the South West, in places such as Cornwall and the Dartmoor area of Devon. The wonderfully lunar-style landscape is formed by the heaps of by-products remaining after the extraction process, much of it quartz. One of these minerals is Mica, the high content of which causes discoloration of the water. Hence, the gorgeous turquoise lagoons.
I could almost imagine the tracks belonging to a moon vehicle. I don't know if the site was still being worked at the time, but all was quiet and deserted. There were outbuildings near the entrance to the site but for some reason I didn't think to explore or take photos of them when I had the opportunity.
Below, the quarry and lagoons seen from the road.
A few more photos along with these can also be seen in the Photo Gallery album.