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

From ore materials to precious gemstones, minerals play an important role in almost every aspect of our lives. This session will focus on characterization of economic minerals employing spectroscopic techniques, geochemical analysis, and microanalytical techniques.

Monday, 20 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1

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

Paper number: 113-7
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM

Authors

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 19th and early 20th 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 Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-413039

© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.