That's wildly misunderstanding things. The fed doesn't trade, regulate, hold or sell gold. That price you're quoting is for a historical artifact called a Gold Certificate. These things have a value set by law (not by the fed) of 42 and 2/9th dollars. They don't sell them anymore, but if you happen to have one they're required to buy it from you (IIRC) at that rate.
As always, Wikipedia: https://en.wikipedia.org/wiki/Gold_certificate_(United_State...