The U.S. Mint Coins:
The New Orleans Mint was one of the three original branches of the U.S. Mint authorized by Congress, and the first branch U.S. Mint to strike coins. Founded to support the exploding growth in the southeast United States and the large amount of trade down the Mississippi River to and from foreign ports, it is the only U.S. Mint besides the original Mint in Philadelphia that was not constructed to exploit local gold or silver discoveries.(The West Point Mint was originally constructed as a bullion depository.)
Upon the outbreak of the Civil War, the Mint and its stores of precious metals and coins were seized by the state of Louisiana. The Confederate government minted its own coinage at the New Orleans Mint briefly, and surviving samples are some of the most rare and sought-after of U.S. coins. The facility was the only one of the three original branch U.S. Mints to be reopened after the Civil War, but it wasn't until 1879 that the New Orleans Mint was refurbished and put back into service.
The Bland-Allison Act of 1878 ordered the Treasury Department to produce at least $2 million of silver coins every year. The New Orleans Mint, which had been re-opened as an Assay Office in 1876, was refurbished to assist in making enough Morgan dollars and other silver coins to fulfill this mandate. Minting operations in New Orleans ran from 1879 to 1909, when excess capacity in the U.S. Mint system and the deteriorating condition of the Mint led to the termination of coin production there. The minting equipment was removed in 1911, and the facility was used for various purposes until it was given over to the state in 1966.
Since 1979, the Old New Orleans Mint building has been part of the Louisiana State Museum system. It is on the National Register of Historic Places, and, according to the U.S. Mint website, is the oldest surviving building to have served as a U.S. Mint.
The New Orleans Mint used the “O” mint mark.