Postcard from the Field: Drone Radiometric Survey of New Mexico Mine Wastes with the USGS

Postcard from the Field: Drone Radiometric Survey of New Mexico Mine Wastes with the USGS

Evan Owen and Ginger McLemore

Mine wastes, including mill tailings (the byproduct of mineral processing after ore minerals have been separated from ore), waste rock piles (non-ore that must be removed to mine ore), and mine water are being examined as potential sources of critical minerals. Critical minerals are materials that are important to a country’s national security, economy, and have supply chains that are vulnerable to disruption. In the United States, the USGS has defined 50 critical minerals, many of which are important for green energy technologies. The New Mexico Bureau of Geology and Mineral Resources is working closely with the USGS to inventory and characterize mine wastes in New Mexico. Recently, we had the opportunity to test a new method for characterizing mine wastes: radiometric surveys using an unmanned aerial system (UAS), more commonly known as a drone.

Research geophysicists Anji Shah and Chloe Gustafson, along with UAS pilots Matt Burgess and Joe Adams, met up with Ginger McLemore and Evan Owen to survey mine wastes in the Black Hawk district near Silver City and the Copper Flat mine near Hillsboro. Summer interns from the EarthScope Consortium and several of Ginger’s graduate students joined the group for a day at the Copper Flat mine to assist and learn about mine wastes. The Black Hawk district contains five-element arsenide veins which are locally rich in native silver and cobalt and nickel arsenides. The mines produced significant silver in the late 1800s, but no cobalt, nickel, or arsenic were recovered. Cobalt, nickel, and arsenic are now critical minerals. The Copper Flat mine is a small porphyry copper deposit which briefly operated in the early 1980s and produced mill tailings and waste rock piles. Critical minerals associated with porphyry copper deposits include tellurium, zinc, selenium, and rhenium.

A large drone equipped with a sensitive gamma ray spectrometer, capable of distinguishing the radioactivity from naturally occurring sources such as potassium, uranium, and thorium, was flown low to the ground over waste rock piles in the Black Hawk district, as well as tailings and waste rock piles at the Copper Flat mine. After processing the radiometric data, the groups will be able to correlate the radiometric anomalies with previously collected geochemical data. Initial results have already highlighted areas at each site that warrant further geochemical sampling.