Deep inside the Dolaucothi Gold Mine is the ore layer we can see here.The rusty narrow band in the lower half of the image,although it's really in the ceiling.Called Mitchell's layer,after the engineer who found it.It's in the ceiling of the passage and is the richest seam in the mine,yielding 2 to 3 times as much gold as any other seam.Sadly,it can't be mined as the Romans found it and quarried it from above.Their shaft is now flooded and it is feared that disaster would strike if it were to be mined.That's not superstition,that's the real fear that the ceiling would cave in.
see http://en.wikipedia.org/wiki/Dolaucothi_Gold_Mines
The wedding ring worn by Diana,Princess of Wales,was made entirely of gold from this mine.