COMEX gold shot to its highest price in 20 days at the open Tuesday, catching some traders wrong-footed as they awaited a Federal Reserve decision on interest rates in the afternoon.
The central bank was expected to raise the target for the federal funds rate on overnight lending between banks a quarter percentage point to 1.75 percent.
An announcement is expected after gold market closes, around 2:15 pm EDT (1815 GMT).
That would be the third rate hike since June, when the Fed began a measured ratcheting up of rates from their lowest levels in 45 years to reverse a policy of accommodation in place since January 2001.
December gold at 9:15 am EDT was up $3.70 at $410.70 an ounce, trading from $406.20 to $412, its highest since September 1, shortly after the open.
"We were calling it $1.50, maybe $2, higher at best. It's probably just a question of buy stops," said a floor broker.
Important technical support in December gold held on Monday at $405.50, the 200-day moving average. Stop-loss buying accelerated Tuesday's move above $408.50 and $409.50.
Spot gold fetched $408.65/9.40, up from $405.00/5.70 late Monday. London's morning fix was $405.45 on Tuesday.
December silver was 8.0 cents firmer at $6.36 an ounce, trading from $6.38 to $6.265. Spot silver was at $6.31/34, up from $6.23/26. The fix was $6.28. October platinum was up $10.10 at $852 an ounce. Spot platinum was at $848.00/853.00. December palladium was up 75 cents at $209 an ounce. Spot palladium was last at $204.00/209.00.