TAMPA, FLA., JUNE 17 -- The discovery of a gold bar from a sunken Spanish galleon indicates that the ship was part of a fleet decimated by a hurricane in 1622, treasure hunters excavating the vessel said today.

"We were both surprised and delighted to find it," said Dan Bagley, a partner in Seahawk Deep Ocean Technology.

The Tampa-based underwater exploration firm has been mapping the shipwreck located 75 miles from Key West, Fla., with a deep-sea robot.

The 1-pound 8-ounce gold bar has tax markings on it that indicate it was part of a fleet of Spanish treasure ships headed for Europe, Bagley said. The bar, 20.3 carats of pure gold, has a raw value of $8,000, but its historical value makes its worth closer to $100,000, Bagley estimated.

Similar marks have been found on three gold bars recovered from the Spanish galleon Nuestra Senora de Atocha, one of nine ships sunk in 1622 during a hurricane. That shipwreck was salvaged by treasure hunter Mel Fisher and yielded more than $200 million in gold, silver, emeralds and other valuable artifacts, which were scattered over 11 miles, complicating the salvage operation.

But the nearby shipwreck that Seahawk has just started excavating, which has not yet been identified by name, lies in 1,500 feet of water and has been undisturbed by waves over the centuries.