Spectroscopy and Hyperspectral Imaging of Critical Mineral Resources

Scientific Issue and Relevance

Critical minerals are essential to National security and economic prosperity of the United States. The U.S. relies heavily on imports of critical minerals, making us vulnerable to natural and foreign events that disrupt our supply chain. In response to the Presidential executive order on a federal strategy to ensure secure and reliable supplies of critical minerals, we will apply cutting edge hyperspectral imaging technology to study critical mineral deposits and the geologic settings in which they are found. By measuring the absorption of light as a function of wavelength, spectrometers can identify minerals and chemical variations in minerals. Imaging spectrometers, commonly known as hyperspectral imagers, can map the distributions of minerals and variations in mineral chemistry at laboratory, field, and aircraft spatial scale.

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Methods to Address Issue

This project proposes to increase our understanding of the spectral indicators of critical minerals using lab-based studies of hand specimens and drill core, hyperspectral field scanning of outcrop and mine pit walls, and hyperspectral images collected from aircraft over focal sites and regional areas. Objectives are to:

• Identify spectral indicators of critical mineral ores and associated mineralogy
• Apply laboratory-, field-, and aircraft-based hyperspectral imaging to studying critical minerals
• Focal studies on rare earth elements (REEs) and lithium (Li)-bearing clays
• Publish critical mineral-related spectra and hyperspectral images
• Create regional mineral maps in the southwestern U.S.

Spectral Investigation of Critical Mineral Ores: Concentrate on collecting and interpreting imaging spectroscopy data of the USGS Historic Ore Collection (which contains over 1700 primary ores from historic mining districts), pure mineral samples, and selected field samples in support of other Mineral Resources Program science projects. Results will provide the fundamental research essential for future laboratory, field and airborne imaging spectroscopy investigations.

Spectroscopy of Lithium-bearing Clays and REE-bearing Minerals: Most Li-bearing clays in the U.S. require expensive roasting for liberation from octahedral layers. Li in the interlayer sites can be leached at a lower cost, potentially increasing the number of economically viable Li deposits in the U.S. Recent work with vermiculites suggests reflectance spectroscopy might determine where Li resides in clays (octahedral vs. interlayer sites). Initial work will involve enriching vermiculite and montmorillonite clay with Li and defining the spectral changes caused by enrichment with interlayer Li. While initially lab-based, if results indicate an interlayer Li spectral signature, available hyperspectral images from related mineral resources science projects will be analyzed.

Airborne Hyperspectral Imaging of Critical Minerals and Mineral Resources: Most existing hyperspectral datasets and surface mineral maps for the U.S. are limited in geographic scope to small areas less than 100 km². Building on methods developed for hyperspectral imaging of Afghanistan, we will utilize recent collections and existing publicly-available archives of hyperspectral data to prepare regional mineral maps in the southwestern U.S. for mineral resource studies and focused studies. 

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