43 CFR § 3832.32
How much land may I include in my mill site?
June 11, 2020
The maximum size of an individual mill site is 5 acres. You may locate more than one mill site per mining claim if you use each site for at least one of the purposes described in §3832.34 of this part. You may locate only that amount of mill site acreage that is reasonably necessary to be used or occupied for efficient and reasonably compact mining or milling operations.