Fee mining sites are commercial mines which earn money by selling permits for digging. Most well known are sites which allow gold panning. But there are also many sites which offer minerals or semi precious and precious gems.
There are two different kinds of such mines. Either you pay a fee for a certain amount of time and keep whatever you find. Others do not restrict the time, but you have to pay anything you want to take home, in general by weight.
To make sure that the customers find something when collecting, regular replenishment must be ensured. This requires active efforts of the operator. If the collection point is located directly on the deposit, overburden produced by visitors must be removed, or overburden from the actual mining must be piled up regularly.