How about getting a prospectors license and going through the 'back door' (so to speak...) Most farmers have no problems with mineral prospectors accessing their property and, I am a little sketchy on the details here, I believe that they can't refuse you access on a regular pastoral lease (you are required to ask permission, but, as they only lease what's on top of the ground - not what's beneath it - , they are required to grant you 'reasonable access').