Florida Law does allow for mineral rights.
This article on eHow.com gives a brief explanation of how they work and cites some references in Florida Statutes. In looking briefly at the statutes, it would appear the article is on target (although I'm not a lawyer, so I could be wrong).
The short version is that it is
possible that GSO owns only the surface land, but unlikely. One would have to look up the records for the real estate transaction where GSO purchased the land and determine if transaction was "fee simple" or not. It is, however, possible that the State reserved mineral rights to the land if the property was purchased directly from the State prior to 1986 and/or in a parcel larger than 20 acres. I don't know the history of GSO well enough to answer those questions off the top of my head.
Brian