Goldman expects gold to average $1,800 an ounce in 2013, down from its previous forecast of $1,940 an ounce.

The call is based on the assumption that real interest rates will gradually begin to rise from record lows as the U.S. economy strengthens in the second half of the year.

"Our expanded modeling suggests that the improving U.S. growth outlook will outweigh further Fed balance sheet expansion and that the cycle in gold prices will likely turn in 2013," the report sates. "Risks to our growth outlook remain elevated however, especially given uncertainty around the fiscal cliff, making calling the peak in gold prices a difficult exercise."

Difficult indeed.