It ceased operations in 1958 and its owner, Arthur Montgomery, donated it to the University of New Mexico, which runs the site as an outdoor geology laboratory with mineral collecting permitted on a small scale.

[2][1] Although the quartz pegmatite had attracted the attention of prospectors since before 1900, the extensive deposits of lepidolite were not recognized until 1918 by Joseph J. Peyer.

This represented a modest profit over the three years of mill operations but a net loss for the entire period of mining.

High demand for tantalum in 1942 for wartime production, and reports going back to 1931 of microlite at the Harding Mine, led Arthur Montgomery to investigate the old workings.

Concentration of the small but rich quantity of highly valuable ore was problematic, but the U.S. Bureau of Mines Testing Laboratory in Rolla, Missouri, used an experimental gravity separation method to process 33.5 tons of ore and extracted 6137 pounds of 77.55% niobium-tantalum oxide.

Ore production reached a ton per day, in spite of the difficulties of hand sorting the beryl from the nearly indistinguishable feldspar and quartz gangue.

Production averaged 100 tons per year until 1950, when the death of Montgomery's partner, Flaudio Griego, ended mining operations.

The sugary albite zone formed from a residual Na-rich magma as a response to late-stage pressure release.

The university leased the property for four years while making numerous improvements, which include a walking tour of the mine.

Because the mine property included both patented and unpatented claims, transfer of the title required an act of Congress (Senate Bill 1403).

Persons wishing to visit the mine must contact the chairman, Department of Geology, University of New Mexico, 87131 to obtain permission (which is almost always granted) and release forms.