If you did find some place on BOR land that you might want to mine there is a process to petition the lands to be restored to mineral entry.
especially if the lands were not used as planed or don't interfere with other uses, and have valuable mineral potential...
https://www.law.cornell.edu/uscode/text/43/154
The authority of the Secretary to open withdrawn lands is conferred by the Act of April 23,
1932, 43 U.S.C. § 154 (1982), which reads, in pertinent part:
Where public lands of the United States have been withdrawn for possible
use for construction purposes under the Federal reclamation laws, and are known or
believed to be valuable for minerals and would, if not so withdrawn, be subject to
location and patent under the general mining laws, the Secretary of the Interior,
when in his opinion the rights of the United States will not be prejudiced thereby,
may, in his discretion, open the land to location, entry, and patent under the general
mining laws, reserving such ways, rights, and easements over or to such lands as
may be prescribed by him and as may be deemed necessary or appropriate,
including the right to take and remove from such lands construction materials for
use in the construction of irrigation works
https://www.oha.doi.gov/IBLA/Ibladecisions/096IBLA/096IBLA379.pdf