(CNN) -- Gold is always worth its weight in, well, itself. Sometimes, it's worth even more.

A gold nugget, weighing 100 troy ounces, sold at auction in Sacremento for $400,000 Wednesday night.

"We valued it at around $200,000," said Amy Baker, auction manager for Holabird-Kagin American. "There were 6 to 7 people bidding on it, most of them anonymously. It went to an anonymous (phone) bidder."

Baker said the auction house may be able to release more information on the winning bidder Thursday.

Security is important when you're dealing with a large hunk of precious metal.

"The new owner, I'm not sure when it will exactly be delivered to him," Baker said. "That's confidential."

On Wednesday, gold closed at $1,396.10 an ounce on the New York Mercantile Exchange, making the nearly 7-pound nugget worth about $140,000, if it were melted down.

But since the nugget, found last year in Nevada County, California, is believed to be the largest one left from the state's gold rush, it has special value. An estimated 500,000 people traveled to California between 1848 and 1864 in search of instant wealth.

"It's the last one we know left in existence," Baker said. "There have been larger ones over the years, but they have been melted down."

The nugget will be on display this weekend at the Sacramento Convention Center, she said.

The California Natural Resources Agency says the largest nugget ever mined in the state was found in 1854 and weighed 195 pounds.

CNN's Nick Valencia contributed to this report