A 1794 silver dollar realised $470,000 in Heritage Auctions' November 14-15 sale of pieces from the Eric P Newman collection in New York.
The lot is one of the first 2,000 struck at the US Mint to cover the sureties for the newly appointed treasury officers under section 5 of the mint act of 1792.
The bill states: "and be it further enacted, that the said assayer, chief coiner, and treasurer, previously to entering upon the execution of their respective offices, shall each become bound to the United States of America, with one or more sureties to the satisfaction of the Secretary of the Treasury, in the sum of ten thousand dollars, with condition for the faithful performance of the duties of his office."
The coins were issued for assayer Albion Cox and coiner Henry Voigt, neither of who had the funds to raise the necessary sum.
Congress made the decision to lower the bond for both men.
First year silver dollars are among the most desirable US coins ever issued.
Another specimen, believed to be the first ever struck at the Mint, realised $10m at Stack's Bowers last year.
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