That makes no sense. They supposedly already have over 8 tonnes of a precious metal lining some vault, why not back it with that? The problem is so do a lot of other people so the value of every other Tom, Dick and Vladimir's gold goes up as well. At least they can monitor the amount of tungsten going into the new coin.

http://www.zerohedge.com/news/2013-01-04/art-cashin-trillion-dollar-coin-alchemy