The bronze medals are largely copper because burnished bronze and gold are similar in color, and the mint did not want any confusion as to which medal an athlete receives.
VOA: standard.2010.02.16
And yet, somehow, they found time this week to debate things like whether or not we should mint coins to celebrate the Baseball Hall of Fame.
The blank planchets are not made at the Mint, which hasn't had the production capacity for this stage of the minting process since the budget cuts of 1981.