Evans, 60, set out this week with deep-ocean explorer Odyssey Marine Exploration Inc. (OMEX) to revisit the remains of the 19th-century sidewheel steamer, which sank in 1857 with the loss of 425 lives and an undetermined amount of gold. Despite recovery efforts in 1989 through 1991 that netted more than two tons of the precious metal, Odyssey says there may still be $86 million of gold lying more than a mile below the surface of the Atlantic.

“This is the greatest lost treasure in United States history,” Evans, who was chief scientist on the earlier expeditions, said in a phone interview before the ship sailed.

Even with the plunge in gold last year, the metal is still more than triple its price in the early 1990s, when previous recovery efforts were suspended because of legal battles over rights to the treasure. And the rare coins that have been found at the site are selling for much more than their weight in gold.