Verified Answer :

The  heating of the metal would result in an energy expenditure
that would make mining copper counterproductive 

The expenditure of the process is comparative
to how much material (rock, dirt, whatever) you have to process. The more will
be the  material to be route, the larger  will be the equipment, or the longer you have
to run it, and the more power and other other materials you need. so that is why its expensive to extract copper from contaminated lan

hope it helps

hope it helps