The Treasure

A Spanish ship that had sunk in 1715, has recently been discovered in the Atlantic Ocean. The Schmitts, an American family of treasure seekers, found the remains of the ship at Fort Pierce, some 210 kilometres(kilometers-US spelling) to the north of Miami. In the ship, there was a treasure which was worth more than a million dollars. The loot includes 51 golden coins, a twelve metre(meter) long ornamental gold chain, and a very rare Spanish coin called, "real." According to the law, the state of Florida is entitled to keep a 20% of the loot. The remaining 80% will be split between the Schmitt family, and a company that owns the rights to the ship wrecks.

Interesting article and very well written!  

1.  The phrase, "had sunk," is perfectly fine to use, but my personal preference would be to omit it.  To me, it sounds more natural without it.

2. Here in the US, we spell metre as, "meter."  "Metre," is utilized pretty much everywhere else.

3. It is more natural to say, "gold coins," in this context.  

4.  Periods and commas always go inside quotation marks.  Examples:
The sign said, "Walk." Then it said, "Don't Walk," then, "Walk," all within thirty seconds.
He yelled, "Hurry up."