Gold SBA

No such thing exists, it is certainly gold plated(with less than $1 worth of gold I might add). As a side note, there were 39 Sacagaweas struck on 1/2oz Gold Eagle planchets during the summer of 1999. None of them have made it outside of US Mint hands and they are currently stored at Ft. Knox.
http://www.smalldollars.com/dollar/page20b.html

If it is a 1999 SBA there is also the chance that it is struck on a Sac blank. I would agree though, most likely it is just plated. There is no way it could accidentally struck on a gold planchet. All the gold is struck at West Point and all the SBA's were struck at Denver and Philadelphia. That makes even a deliberate striking unlikely since not only would you have to smuggle the coin out, you would have to smuggle the planchet in. And where would you get a gold planchet? You might smuggle in a 1/2 oz AGE, but then you would have a coin from one facility struck over a coin from another one, an obvious fabrication.

Just ask him what it weighs. An SBA weighs 8.1 grams, a gold planchet the same size weighs 17 grams. More than twice as much.

I just happened to stumble upon this Link