Much of the gold available today came from very deep mines in South Africa. Some of these go down 2000 to 3000 meters and must be artificially cooled for the miners to work that deep. If the sunken treasure's location is known and there is sufficient quantity, somebody will eventually find a way to bring it up.

Note: US American Eagle 1 oz gold coins are now selling over $1000 each if you can find a dealer who has any. These are not proof or rare collectibles, just a lump of gold that is easily identified and resold.