Ron Paul wants to find out.

Giving legitimacy to an Internet conspiracy theory that the gold in Fort Knox is fake, the iconoclast Republican congressman from Texas has asked adminstration officials to audit the purity of the nation's 700,000 gold bars held in Fort Knox, according to an internal Treasury document obtained by CNBC. Paul, a presidential candidate who chairs the House's subcommittee on Domestic Monetary Policy, had previously called for the U.S. gold reserve to be counted and for a return to the gold standard. He now appears to be going a step further in his request that representatives from the U.S. Treasury Department and the U.S. Mint testify at a subcommittee hearing on June 23 about the authenticity of the nation's gold.

The Treasury document says it would cost about $15 million to conduct an audit. The process would take about 30 minutes to verify the gold content of each bar, or 350,000 man hours; to do that would would take 400 people working for six months, according to the document. The Mint is audited annually by the Treasury's Office of the Inspector General. An audit of the "Schedule of Custodial Deep Storage Gold and Silver Reserves" was published in September 2010.

A Google search of the phrase "Is the gold in Fort Knox fake" returns 623,000 results. Many of them reference a single, unverified report in 2009 that the Chinese received a fake shipment gold that, in fact, was tungsten.

One conspiracy theory says that no one has actually seen the gold since the 1930s. But in a letter to Paul in September, the Treasury Inspector General said he had "personally observed the gold reserves located in each of the deep storage compartments."

As a postscript to the story, CNBC asked for a tour of Fort Knox to film the gold, since our only footage of Fort Knox is from 1974. An official at the Mint told us that not he was not aware that any member of Congress had toured the facility since that year. Fort Knox is "a closed facility," the official said.

And so the conspiracy theory continues...