Two 1964 American Philadelphia and Denver Mint sets, each containing 5 uncirculated coins from that year. The coins are stored in plastic holders to preserve their condition and prevent damage. These sets hold historical significance as 1964 was the last year that circulating US silver coins contained 90 per cent silver content before the transition to base metal coinage. The Philadelphia and Denver mints were two major minting facilities in the United States. Vintage American Coins And Numismatic Collectibles.