[jacquesm]

Hm... maybe. Especially copper is not so easily separated from the substrates in which it is used, for an electric motor it is fairly easy but all of the copper embedded in millions of miles of wiring (which of course you can cook, but the fumes that will produce are going to be extremely dangerous, think dioxins) it may not be quite so easy.

The advantage of most copper deposits in their natural form is that the rock can be crushed and the tailings are uniform and mostly heavy and inert. For what you'd get out of a 'former city' it would be far less dense in terms of copper and steel than a mineral rich vein. I think before we'd go for the cities themselves there would be the dumps and then the deposits that are today not economically feasible. Long after that the cities.