Mineral rights give you ownership to the minerals beneath the surface of the land, not rights to the land. You cannot gate anything just because you own mineral rights...you have to have land rights for that.
However, you don't own a body of water unless you own every inch of land all the way around it, with no exception. Any water accessible by boat from public waters (without getting out of the boat and trespassing on private lands) is public water. You cannot impede access to it, even if you own the land on both sides. That's the law. The penalty is actually very steep (possibly including jail time) for doing this, because you are intentionally creating a water hazard (the gate) that endangers lives.
If this weren't the case, nobody would ever be able to go tubing down a river, as every landowner down the river would put a fence across it.
Here is a site that lists the language in Louisiana law stating that all navigable waterways are public:
http://www.segnette.com/access