According to the International Copper Association, more than 80% of all copper ever mined is still in active use. Copper doesn't materially degrade in use -- used material can simply be recast or rewrought for a new use.
Any physics textbook. Look up "conservation of mass".
I think _exec was asking for a source to back up the claim about the pharaohs' copper mines.
Yes. I couldn't find anything online about that :)