The Harding Pegmatite

A university owns this mine and lets people collect on it.

The Harding Pegmatite Mine is a former adit mine in Taos County, New Mexico, which took lithium, tantalum and beryllium out of a Precambrian pegmatite sill. It stopped work in 1958, and its owner Arthur Montgomery gave it to the University of New Mexico. The university runs it as an outdoor geology laboratory, with mineral collecting permitted on a small scale. The US Geological Survey lists it as a past producer of beryllium, lithium, tantalum, niobium and calcium, about 19 miles southwest of Taos, and records its older names: the Harding Mine, the Lepidolite Mine, the Lithia Mine, the Glass Mine.

Prospectors had noticed the quartz pegmatite since before 1900, but nobody recognised the extent of the lepidolite until Joseph J. Peyer did in 1918. Peyer and his partners blasted the ore body, sorted the rock by hand, and hauled it by wagon to Embudo, where the nearest railway was. Lithium then went mainly into specialty glass. The trouble was that the ore carried tantalite nobody had identified, which caused real problems in use, and production stopped in 1924.

The Embudo Mining Company took it on that same year, built a mill, and restarted in 1927. The main ore body was worked out by 1929 and the mine shut in 1930, having produced about 3,500 tons of ore worth roughly 140,000 dollars. That was a modest profit across the three years of milling and a net loss over the whole life of the mining.

The war changed the arithmetic. Demand for tantalum in 1942, plus reports going back to 1931 of microlite at the Harding, brought Arthur Montgomery to look through the old workings. He found rich material still in the dumps and at the east end, took a lease purchase on the property, and with six local miners cut ore out with chisels and sorted it by hand. Concentrating it was the hard part, but the US Bureau of Mines laboratory at Rolla, Missouri ran 33.5 tons through an experimental gravity separation and pulled out 6,137 pounds of 77.55 per cent niobium-tantalum oxide, the largest single unit of American tantalum production ever recorded.