Louis,
I do not know the answer. I do know that in Texas, minerals that are mined by disturbing the surface, belong to the surface owner. I was involved in lignite (low grade coal) mining from railroad lands in the 1980-1990's. The RRC administered the open pit operations along with a great deal of input from the counties and the Authority involved. i.e. the LCRA who was the ultimate consumer of the lignite.
Call a sand and gravel provider and find out who issues their mining permits. I'll bet that the county is involved at some level.
Gary Hutchinson