Failure to file by August requires BLM to declare the claim or site null and void by operation of law. Mineral patent applicants who have been issued the first half of their mineral entry final certificate are exempt from payment of fees or performance of assessment work. Assessment work is work or labor performed in good faith that tends to develop the claim and directly helps in the extraction of minerals. Geological, geophysical, and geochemical surveys may qualify as assessment work for a limited period. However, a requirement for use of these surveys is the filing of a detailed report, including basic findings.
Most State laws require the annual filing of an affidavit of assessment work with the proper county.
Assessment work is not a requirement for owners of mill or tunnel sites. For mill sites and tunnel sites, filing with the county is not required. Performance of assessment work must be within a certain period referred to as the assessment year. The assessment year begins at noon, September 1. Performance of assessment work need not occur during the first assessment year of location.