 The catalog number of the 2006 proof coin at the U.S. Mint is (BA6).The coin was created in order to compete with foreign 24-karat gold bullion coins.Since investors sometimes prefer 99.99% pure gold over the 91.67% gold used in the American Gold Eagle, many were choosing non-U.S. coins, such as the Canadian Gold Maple Leaf, to meet their bullion needs.