The Mining Law of 1872 allows people to prospect for valuable minerals on public lands. Prospectors can “locate” or “stake” mining claims.

Claimants can also locate “mill sites” for milling or other mining-related activities.[1]

Mill sites can be used for processing facilities and other structures to support the extraction of minerals from a mining claim. Existing regulations allow mill sites to be used for rock and soil storage, ponds, leach pads, and other uses that are “reasonably incident to mine development and operation.”[2]

A mill site cannot be larger than five acres.[3]

In 1999, the Bureau of Land Management (BLM) proposed a regulation to limit mining claimants from locating more than one mill site for each mining claim. In other words, the regulation proposed a one-to-one limit on mill sites and mining claims.

Later, in 2003, BLM promulgated a Final Rule withdrawing the proposed 1999 regulation. The Final Rule did not limit the number of mill sites that may be claimed, consistent with decades of precedent. The Final Rule did, however, state that mill sites must be “reasonably necessary” for “efficient and reasonably compact milling or mining operations.”

In 2009, several conservation groups sued BLM in U.S. district court challenging the validity of the 2003 Final Rule. The conservation groups asserted that the Mining Law of 1872 unambiguously limits claimants from locating more than one mill site per mining claim. The district court ruled in favor of BLM and upheld the 2003 Final Rule.

In a decision filed on June 25, 2024, the U.S. Court of Appeals for the District of Columbia Circuit affirmed the district court’s decision to uphold the 2003 Final Rule. The majority opinion stated that it had “no difficulty” concluding that the interpretation of the Mining Law of 1872 in the 2003 Final Rule “represents the better reading of the statute.”

The dissenting opinion refers to the 2003 Final Rule as the “‘unlimited mill sites’ approach.” Although the now-codified regulation does not limit the number of mill sites that a claimant can locate, it states that mill sites must be limited only to what is “reasonably necessary” for “efficient and reasonably compact milling or mining operations.” Thus, there is a limit on lands that may be staked as a mill site.

This is an important development for the mining industry because a one-to-one limit on mill sites and mining claims would significantly curtail the ability of operators to develop mineral deposits. Mineral deposits vary greatly in size and scale, and different types of minerals must be mined and processed via different methods with different equipment. Thus, the number of mill sites necessary for mining depends on the unique details of each individual operation, including topography.

A copy of the D.C. Circuit decision is available here.

[1] 30 U.S.C. § 42(a); 43 C.F.R. § 3832.31. 

[2] 43 C.F.R. § 3832.34.

[3] 30 U.S.C. § 42(a); 43 C.F.R. § 3832.32.