Various rules in Federal Register have hindered mineral exploration in the National Forests. These are contrary to the mining act of 1872. Below are two urls which describe the situation.
the ban on metal detecting:
https://www.fs.usda.gov/activity/cherokee/recreation/rocks-minerals/?recid=34864&actid=60
general info:
https://www.fs.usda.gov/geology/includes/minerals/1975MiningInNationalForests.pdf