Are you panning , detecting , beach detecting, sluicing or open cut mining with big yellow machines ?
Every state has its own rules and regulations and permit/license systems.
Its complicated with public land , state forests , national parks , conservation areas , recreation land ,fossicking areas , crown land, commons , lease land , private land and many more.
Searching for fossicking areas for each state you plan to be in and looking at the government sites for locations and laws would get you started.