Gold traded at $646.50 an ounce, down $2.20 an ounce from Wednesday. The euro lost ground against the U.S. dollar ahead of Thursday''''s European Central Bank interest rate decision. The euro bought $1.2760 in early European trading, down from $1.2798 in New York late Wednesday. The British pound dropped to $1.8746 from $1.8779. The dollar also climbed to 114.76 Japanese yen from 114.55 yen.