Investors run to gold after Fed promises action

Gold and silver, which had traded flat to slightly down throughout the morning, shot up after the Fed released its decision at 12:30 p.m. EDT. Gold finished more than 2 percent higher. Silver jumped more than 4 percent.

Investors often put their money into gold when the Fed gets more involved in the economy. Fed actions carry the risk of causing inflation. Some investors view gold as a way to protect themselves from rising prices.

Gold for December delivery jumped $38.40 to $1,772.10 per ounce. December silver jumped $1.486 to $34.778 per ounce.

Some wondered how long the increase would last. Both gold and silver have been rising since the start of August, because investors were already expecting the Fed to take action.

"We suspect that the uptick could morph quickly into a light round of profit-taking, since much of the Fed move is already baked into prices," Edward Meir of INTL FCStone wrote in a note to clients.

The moves in gold and silver also boosted other key metals.