113-8 Rare Earth Elements in Legacy Mine Tailings from French Creek Mine, Chester County, PA

Session: Mineralogical Characterization of Economic Resources: From Critical Minerals to Gemstones (Posters)

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Abstract:

Critical minerals are required to manufacture essential technology for the energy transition, communications, and transportation. Many of these minerals are not currently mined and processed within the United States, and must be imported. Iron mines were active in PA in the 19^th and early 20^th Centuries, and a legacy of mine waste and slag is now found at or near the surface. Analysis of iron furnace slag from Southeastern PA has revealed high concentrations of Rare Earth Elements (Total REE up to ~1,000 ppm), but the geological source of the REEs remain unknown. Preliminary assessment of mine tailings revealed the presence of allanite (REE-bearing epidote). The French Creek Mines in Chester County, PA, sit on top of an area where Jurassic diabase intruded into Precambrian gneiss. Magnetite skarns forming in these areas have historically been mined for iron and copper, and may have high concentrations of associated REEs. We hypothesize that a significant amount of REEs, not yet of interest at the time of active mining, may be hosted in allanite within legacy mine wastes from the French Creek Mine in southeastern Pennsylvania.

Using the MapsMin automated mineralogy software package with the ThermoFisher Apreo 2S FE-SEM, we mapped the modal mineralogy of historic mine tailings from French Creek. This allowed us to confirm the presence of allanite as the primary host of REE. Our samples were scanned with a custom recipe within the MapsMin software, which allowed us to focus the machine’s rendering power on only mapping out specific minerals of interest. Several of these samples were also scanned more precisely using a Cameca SXFive electron probe micro-analyzer (EPMA). The highest amount of allanite was found in the >150 micron size fraction, at 1.6 weight%. The smaller size fractions had ~1.0-1.4 weight% allanite. EPMA analysis showed 5-15 weight% total REEs heterogeneously distributed within the allanite.

Rare earth elements may be able to be recycled and harvested from French Creek Mine tailings if allanite is separated from the bulk mine waste. The processes used here could also be used to identify critical materials in mineral waste from modern industrial processes, making them more efficient and less wasteful.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8117

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