According to what I can find, they arent plated "gold" by the Mint, at all. They are an amalgam of"
88.5% Cu
6% Zn
3.5% Mn
2% Ni
I havent found any reference to a steel planchet SAC dollar. There were some few that were mis-struck on Maryland quarter planchets and they are worth far more than a dollar. Those have sold for $3500! This has also occured with one MA and one KY quarter. They are obvious offset strikes though, and yours doesn't appear to be one.
There were also some SAC's struck on clad Susan B. Anthony planchets, of which about 10 are known to exist.
There was a mint error referred to as the SAC "not so golden" Dollar, too. Although, that one still looks gold - just "not so golden," thus the name.
And if you rub a common SAC, even go so far as to polish it, they end up looking silvery.
But none of this steel planchet, clad mistrike or polished out SAC stuff accounts for a coin having lain in the ground at 2" and still coming out silvery.
If it is silver, then it is plated or a counterfeit.
Better check with some REAL experts to be sure, Bill. You may have a one of a kind fortune-maker.
Tidbit #2. The SAC dollar has been given approval for continued minting by Congress. Thanks to a bill which has just passed both houses of Congress. H.R. 2358, known as the "Native American $1 Coin Act," the Secretary of the Treasury (and by extension, the U.S. Mint) are required to "mint and issue coins in commemoration of Native Americans." These new Sacagawea Dollars are required to comprise no less than 20% of the Dollar coins issued in a given year.
No reverse is stipulated, so it is expected that there will be new reverse designs, as well. Some ideas that have been suggested are:
Creation of the Cherokee written language
Existence of the Iroquois Confederacy
Chief Massasoit of the Wampanoag
The Pueblo Revolt
Olympic Champion Jim Thorpe
General Ely S. Parker, who headed the Bureau of Indian Affairs
Navajo "code talkers"
The Native American $1 Coin Act also stipulates that the Sacagawea Dollar will get edge incused lettering, to include the following inscriptions: date of issuance, E Pluribus Unum, and In God We Trust.
So, SACKIES's will continue to be minted alongside the Presidential dollar, albeit in limited numbers.