Minerals aren’t owned until they’re brought to the surface. You’re selling the right to access and bring up those minerals. Your contract might specify a lease which could expire, or you might sell outright. You could get a lump sum, or be paid as the minerals are extracted. Educate yourself on the various options and keep in mind these aspects of mineral rights:
Right to reasonable access across the surface
Right to convey rights
Right to renew, extend, or expand rights
Right to bonus considerations or delay rentals
Right to royalties