There are under 10 of these known to be graded by any grading service, and with the over date of 13/12, it makes it exceptionally rare. 
If you look close at the obverse of this piece, you can see the fine striations across the surfaces that you typically see in fresh mint state coins.
Shipwreck gold has skyrocketed in value over the last several years, with many pieces disappearing from the marketplace into private hands. Finding raw examples like this one are quite hard to find, but having friends around the world to help me source material like this has its perks!