Salvation Army (search) officials don't know who has been dropping gold coins into their holiday kettles over the past 20 years, but they hope the mysterious donations continue.

More than 300 gold coins have been collected since the early 1980s, with an average value of about $200 each, said Cliff Marshall, spokesman for the charity in Chicago, where the tradition began.

Chicago bell-ringers have brought in 10 gold coins so far this year. They aren't the only ones.

In Kirksville, Missouri, someone donated a gold coin that was minted 20 years before the Civil War (search), worth nearly $1,000. A South African Krugerrand worth $400 was dropped in a kettle in Bloomington, Illinois, meaning 12 extra families will get a complete Christmas dinner.

But officials still don't know where the coins come from.

The mysterious tradition began in 1982, when someone slipped a gold coin into a kettle in the Chicago suburb of Crystal Lake. The donations have occurred there ever since and have spread across Illinois and about a dozen other states.

The phantom donors almost always conceal the coins, usually folding dollar bills around them. They range from small gold pieces worth about $15 to Krugerrands that can fetch $600 from collectors.

The gold coins have been worth a total of about $60,000. That's just a fraction of the $3.5 million collected by the Salvation Army last year in Chicago. But the mystery donors may have more than money on their mind.

Some believe the coin droppers might have been helped by the relief agency in the past. Or they might just like the thrill of seeing the donation play out in the media. One woman called last summer to say her late mother left gold coins in the kettles each year because she liked the buzz it created, Marshall said.

Rich Draeger, spokesman for Salvation Army's Peoria division, said the timing of the donations suggest they might be an inside job. He said gold coins tend to show up when giving starts to lag, indicating it might an attempt by the charity to generate extra publicity.

"It seems to be a benefactor who knows that it's going to mean a lot more than a $300 or $400 coin — it's going to bring attention," Draeger said.

Daniel Borochoff, president of the American Institute of Philanthropy, a charity watchdog group, doubts the Salvation Army is planting the coins to create publicity.

"They're a heavy-duty Christian group, so that may go against their principles," he said.

Marshall, for one, hopes the mystery is never solved. "It's more fun to speculate than to know for sure," he said.