Mill Site

A mill site is a location of nonmineral land, not contiguous to a vein or lode, that a claimant uses for activities reasonably incident to mineral development on, or production from, the mining claim it is associated with (43 CFR 3832.31).

A mill site is not a mining claim. The regulations for locating and maintaining claims define an unpatented mining claim as a lode or placer claim, and define a site as a mill site or a tunnel site. Both are located, recorded, and maintained under the same parts of the regulations, which is why the phrase used throughout is "mining claims and sites."

Two kinds of mill site

• Dependent mill site: used for activities that support a particular patented or unpatented lode or placer mining claim, or a group of mining claims.
• Independent or custom mill site: not tied to a particular mining claim. It provides milling or reduction processing for nearby lode mines or a lode mining district, either under contract for other miners or on ore the mill owner has purchased. A custom mill site may not be used to process material from placer mining claims.

Size and number

• The maximum size of an individual mill site is 5 acres (43 CFR 3832.32).
• More than one mill site may be located for a mining claim if each is used for a qualifying purpose.
• A claimant may locate only the acreage reasonably necessary for efficient and reasonably compact mining or milling operations.

Requirements for a valid mill site

• The land must not be mineral-in-character (43 CFR 3832.33).
• Each two and a half acre portion of the mill site must be used or occupied for that portion to be valid.
• A mill site may not be located on land where the United States does not own the surface estate.

Uses that qualify for a dependent mill site

Under 43 CFR 3832.34, and with authorization under the surface management regulations of the agency that manages the surface, a dependent mill site may be used for:

• Grinding, crushing, milling, and reduction facilities
• Mine administrative and support buildings, warehouses, maintenance buildings, electrical plants, and substations
• Tailings ponds and leach pads
• Rock and soil dumps
• Water and process treatment plants
• Any other use reasonably incident to mine development and operation, except uses that exclusively support reclamation or mine closure

Recording and fees

A mill site is located in the same manner as a lode or placer mining claim. It is recorded with BLM by the 90th day after the date of location, and it pays the same annual maintenance fee as a lode claim, $200, due on or before September 1.

Reading a mill site in the record

Two of the conditions for a valid mill site cannot be read from a filing. One is whether the ground is truly nonmineral. The other is whether each 2.5-acre portion is actually used or occupied. A mill site that is current in the BLM record has met its filing and payment requirements, and nothing more than that.