fine troy ounce -

"denomination ... in the case of gold, in fine troy ounces of gold (to three decimal places) and; in the case of silver, in troy ounces of silver (to at least one decimal place); in the case of Platinum Group Metals, in troy ounces of the respective Platinum GroupMetal (to at least three decimal places)"

http://www.sizes.com/units/ounce_troy.htm
http://en.wikipedia.org/wiki/Ounce