I have a 2008 ASE that is little heavier than spec and has what looks like Copper under thinning Silver. The Spec weight is 31.10 and this is 31.31.
Upon a quick look, the coin looks ok to me. If that area is pitted, it could be a bad planchet and the darkness is toning. If it is just bullion to you, you can always scratch it and find out what is underneath the surface.