Sampling mine tailings at Carbonate Hill for critical minerals

There are hundreds of tailings in New Mexico, remaining after the mining and processing of ores. Tailings are the solid waste product (gangue and other refuse material) resulting from the milling and mineral concentration process (washing, concentration, and/or treatment) applied to crushed ore. The NMBGMR Economic Geology Group is sampling tailings throughout New Mexico with funding from the USGS Earth MRI critical minerals in mine wastes program, including the Carbonate Hill mine, in the McGhee Peak mining district of the Peloncillo Mountains, Hidalgo County, New Mexico. These tailings could have potential for critical minerals extraction, especially since the mineral production was generally for precious and base metals and not critical minerals. Furthermore, early operations did not have efficient recovery separation techniques; therefore, even the original commodity of interest could be elevated in some mine tailings. A critical mineral is a nonfuel mineral commodity that is essential to the economic and national security of the United States, from a supply chain vulnerable to global and national disruption. Critical minerals are essential to the manufacture of high-tech technologies such as cell phones, tablets, laptops, computer chips, solar panels, wind turbines, batteries, and electric cars. Critical minerals are also used to build desalination plants and carbon sequestration facilities.

The Carbonate Hill mine (also known as the McGhee mine) was discovered in 1894, and much of the production and milling occurred from 1916 to 1948 by the McGhee brothers. Total production from the mine from 1894 to 1956 is estimated at more than 200,000 short tons of lead-zinc-silver ore from carbonate-replacement deposits; reported production grades were 6% Pb, 5% Zn, and 2 ounces/ton (62.5 ppm) Ag. The Carbonate Hill mill was built in 1928, but a fire destroyed the original mill in 1948. A new mill was built around 1955-1956, but not much production occurred. Tailings were deposited in the arroyo draining from the mill. Today, tailings are stored in well-engineered, lined tailings facilities, but when the Carbonate Hill mill operated, depositing tailings in the arroyo or hillside was the standard practice.

New Mexico Tech students collected composite samples from the tailings and the mine waste dump. We transported the samples to our lab at the New Mexico Bureau of Geology and Mineral Resources (NMBGMR) in Socorro for characterization. Characterization will include determining the size, mineralogy, and chemistry of the tailings and mine waste dump samples to identify minerals present. Known mineralogy at Carbonate Hill includes galena, sphalerite, smithsonite, cerussite, chalcopyrite, and pyrite. Potential critical minerals from the tailings could include zinc, tellurium, tungsten, and bismuth. Note that the tailings are gray to yellow in color, reflecting oxidation of the sulfide minerals, especially pyrite.

In 2009-2010, the Bureau of Land Management, in collaboration with the New Mexico Mining and Minerals Division’s Abandoned Mine Lands Bureau, safe guarded 21 mine shafts by backfilling or constructing specialized gates and structures to allow bats and owls to continue living in these underground habitats, while protecting human visitors from the dangers of underground mines. Some of the photos include these structures. There has been no reclamation of the tailings.

For more information about this project, visit our webpage, Critical Minerals in Mine Wastes.