The USGS Airborne Geophysics for Rare Earth Element Deposits (AGREED) project coordinated with industry to use high resolution airborne geophysical data collected over some of the advanced rare earth element (REE) projects in the U.S. These data were analyzed, interpreted and modeled to generate an improved understanding of the geologic setting, framework, and ore genesis for REE deposits. In addition, the project will create a petrophysical library of samples collected from these deposits that will contribute to and compliment the airborne geophysical analyses.

Science Issue and Relevance
Over two dozen rare earth element (REE) deposits have been identified both in the conterminous U.S. (Long and others, 2010) and in Alaska (Barker and Van Gosen, 2010). The majority of larger domestic deposits are hosted in carbonatite or peralkaline intrusions and related pegmatites and veins, which typically make excellent geophysical targets because of their distinct gamma ray, density, and magnetic properties. As such, airborne geophysical surveying is routinely acquired by industry to map the extent of surface and subsurface mineralization related to these deposits. In many cases, geophysical surveying has figured prominently in the initial discovery of REE deposits.
Thus far, no airborne geophysical data have been collected by the USGS at a resolution sufficient for studying the ore genesis, setting, or characterization of REE deposits. Only coarsely spaced airborne magnetic data and ground gravity data exist over these deposits. However, high resolution data over domestic REE deposits are available from the mining industry. Innovation in geophysical methods and model development, expansion of geophysical skills, and keeping current on technological advancements over deposits of strategic importance requires access to modern geophysical data.
Project Objectives
The overall project objective was to coordinate airborne geophysical efforts over domestic REE deposits and create a petrophysical library that will contribute to and complement geophysical model development and characterization of rare earth deposits. Our project:
- Worked with mining industry to obtain high resolution airborne geophysical data over rare earth deposits,
- Created a petrophysical library from surface and core samples that describe the range of petrophysical properties of host rocks, structures, and mineralized systems, with an emphasis on REE concentrations and occurrences,
- Interpreted and modeled the data using modern techniques, many developed in-house.
USGS acquired mining industry data over three advanced REE deposits with active exploration efforts. Initial focus areas were the Bokan Mountain deposit in southeastern Alaska (data acquired from UCore Rare Metals and Precision GeoSurveys, Inc.), Elk Creek deposit in Nebraska (data acquired from NioCorp, formerly Quantum Rare Earth), and the Bear Lodge deposit in Wyoming (data acquired from Rare Element Resources).
High Resolution Geophysical Survey
A high resolution magnetic and gravity gradiometry survey was conducted of the Pea Ridge iron oxide copper-gold rare earth element (IOCG-REE) deposit in southeast Missouri. This survey will be flown by the USGS.
What Constitutes a High Resolution Geophysical Survey?
- Designed to resolve:
- low signal
- information between lines
- Line Spacing / Flight Height: < 2 (Ideal = 1)
- Fly close to the ground with narrow line spacing
All industry surveys were flown at low altitudes (80 to 100 m above ground) with 100 to 200 m flight line spacing. Both fixed wing and helicopters were used.
Low Resolution vs. High Resolution: Scientific benefits of working with high resolution geophysical data are numerous, not the least of which is the wealth of information provided in the detail. The images below show the "before" and "after" of USGS magnetic survey with 1600 m line spacing, compared to the magnetic survey flown by UCore over Bokan Mtn with 100 m line spacing. The resolution provided in the UCore survey allows for detailed mapping of the host rocks, controlling structures, and mineralized system. The UCore data provides more than 10 times the resolution of the older USGS survey.
Multiple Sensors Collecting Data Concurrently: Another obvious benefit working with high resolution survey data is that all the industry surveys had multiple sensors on board collecting data simultaneously. For example, both the Bear Lodge and Bokan surveys include magnetic and gamma-ray data. The gamma-ray data is especially useful over exposed REE deposits as we can begin to understand the relationship between the radioelements (uranium [U], thorium [Th], and potassium [K]) and the concentrations of rare earth elements (REE) within the host and mineralized rocks. For the USGS Bokan study, our geophysicist is working closely with our mineralogist to understand the REE mineralogy as it relates to the uranium, thorium, and potassium minerals. Thru this process, connections are made that allow interpretation of the airborne geophysical data in the context of rare earth deposit setting and mineralization.
Bokan Mountain Deposit, Alaska
Bokan Mountain, located at the southern end of Prince of Wales Island, southeast Alaska, has been the site of past uranium mining and most recently is the focus for exploration of rare earth elements. Bokan Mountain is a peralkaline granite complex with associated dike vein systems that are enriched in a number of heavy rare earth elements (HREE).
An airborne geophysical survey, flown by Precision GeoSurveys and provided by UCore Rare Metals (http://ucore.com/), was recently flown over the Bokan deposit. The survey collected high resolution magnetic and gamma-ray spectrometry data along flight lines spaced 100-m apart. Bokan Mountain objectives are to:
- develop an understanding of the magnetic and radioelement properties of rare earth ore and ore hosts;
- analyze the relation between the rare earth element mineralogy and geophysical properties; and
- develop a regional geophysical characterization of peralkaline intrusion and possible geologic controls on mineralization.
Elk Creek Deposit, Nebraska
The Elk Creek carbonatite, located in southeastern Nebraska, is host to niobium (Nb)-REE minerals and covered by approximately 200 m of sedimentary cover. An airborne geophysical survey that includes gravity gradiometry and magnetic data was recently flown and provides insight into the geophysical expression of a buried carbonatite. These data have been made available to the USGS through a non-disclosure agreement with NioCorp Developments Ltd. (formerly Quantum Rare Earth Developments Corporation), which allows USGS full access to digital flight line data and to publish figures, charts, maps, and interpretations of the data. Elk Creek objectives were to:
- develop an understanding of the magnetic and density properties of the Nb-rare earth ore and ore hosts at Elk Creek;
- develop models of the carbonatite through integration of physical property data collected on drill core and analyses of high resolution geophysical data; and
- develop a model that encompasses geophysical characterization of the Elk Creek carbonatite and possible geologic controls on mineralization.
Bear Lodge Deposit, Wyoming
An airborne geophysical survey, provided by Rare Element Resources (http://www.rareelementresources.com/s/Home.asp), was recently flown over the Bear Lodge carbonatite deposit. The survey collected high resolution magnetic and gamma-ray spectrometry data along flight lines spaced 100-m apart. The map below shows the magnetic anomaly field over the Bear Lodge igneous complex, which hosts the rare earth–bearing carbonatite dikes within the Bull Hill area. Bear Lodge objectives were to:
- develop an understanding of the magnetic and radioelement properties of rare earth ore and ore hosts at Bear Lodge;
- analyze the relation between the rare earth element mineralogy and geophysical properties; and
- develop a regional geophysical characterization of alkaline intrusion, carbonatitic dikes and possible geologic controls on mineralization.
References Cited
Barker, J.C., and Van Gosen, B.S., 2012, Alaska’s rare earth deposit and resource potential: Mining Engineering, v. 64, Issue 1, p. 20-32, http://me.smenet.org/abstract.cfm?preview=1&articleID=2502&page=20.
Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, D., 2010, The principal rare earth elements deposits of the United States—A summary of domestic deposits and a global perspective: U.S. Geological Survey Scientific Investigations Report 2010-5220, 96 p., https://doi.org/10.3133/sir20105220.
The use of firm, trade, and brand names is for identification purposes only and does not constitute endorsement by the U.S. government.
Return to Mineral Resources Program | Geology, Geophysics, and Geochemistry Science Center
Below are other science projects associated with this project.
Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri—From the Ore Deposit Scale to a Global Deposit Model
Continental Scale Geophysics — Integrated Approaches to Delineate Prospective Environments for Critical Metals
Geophysical and Geochemical Approaches to Evaluating Rare Earth Element (REE) Potential in the Southeastern U.S.
Below are publications associated with this project.
Geophysical expression of a buried niobium and rare earth element deposit: the Elk Creek carbonatite, Nebraska, USA
Geophysical interpretation of U, Th, and rare earth element mineralization of the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeast Alaska
Below are news stories associated with this project.
Below are partners associated with this project.
- Overview
The USGS Airborne Geophysics for Rare Earth Element Deposits (AGREED) project coordinated with industry to use high resolution airborne geophysical data collected over some of the advanced rare earth element (REE) projects in the U.S. These data were analyzed, interpreted and modeled to generate an improved understanding of the geologic setting, framework, and ore genesis for REE deposits. In addition, the project will create a petrophysical library of samples collected from these deposits that will contribute to and compliment the airborne geophysical analyses.
Sources/Usage: Public Domain. Visit Media to see details.Principal rare earth elements districts in the United States and location of high resolution geophysical surveys flown by industry and planned surveys (stars). From Long and others, 2010, USGS SIR 2010-5220. Science Issue and Relevance
Over two dozen rare earth element (REE) deposits have been identified both in the conterminous U.S. (Long and others, 2010) and in Alaska (Barker and Van Gosen, 2010). The majority of larger domestic deposits are hosted in carbonatite or peralkaline intrusions and related pegmatites and veins, which typically make excellent geophysical targets because of their distinct gamma ray, density, and magnetic properties. As such, airborne geophysical surveying is routinely acquired by industry to map the extent of surface and subsurface mineralization related to these deposits. In many cases, geophysical surveying has figured prominently in the initial discovery of REE deposits.
Thus far, no airborne geophysical data have been collected by the USGS at a resolution sufficient for studying the ore genesis, setting, or characterization of REE deposits. Only coarsely spaced airborne magnetic data and ground gravity data exist over these deposits. However, high resolution data over domestic REE deposits are available from the mining industry. Innovation in geophysical methods and model development, expansion of geophysical skills, and keeping current on technological advancements over deposits of strategic importance requires access to modern geophysical data.
Helidopter system used by Precision GeoSurveys to fly Bokan Mountain. Maps generated by USGS with data provided by UCore. Project Objectives
The overall project objective was to coordinate airborne geophysical efforts over domestic REE deposits and create a petrophysical library that will contribute to and complement geophysical model development and characterization of rare earth deposits. Our project:
- Worked with mining industry to obtain high resolution airborne geophysical data over rare earth deposits,
- Created a petrophysical library from surface and core samples that describe the range of petrophysical properties of host rocks, structures, and mineralized systems, with an emphasis on REE concentrations and occurrences,
- Interpreted and modeled the data using modern techniques, many developed in-house.
USGS acquired mining industry data over three advanced REE deposits with active exploration efforts. Initial focus areas were the Bokan Mountain deposit in southeastern Alaska (data acquired from UCore Rare Metals and Precision GeoSurveys, Inc.), Elk Creek deposit in Nebraska (data acquired from NioCorp, formerly Quantum Rare Earth), and the Bear Lodge deposit in Wyoming (data acquired from Rare Element Resources).
High Resolution Geophysical Survey
A high resolution magnetic and gravity gradiometry survey was conducted of the Pea Ridge iron oxide copper-gold rare earth element (IOCG-REE) deposit in southeast Missouri. This survey will be flown by the USGS.
What Constitutes a High Resolution Geophysical Survey?
- Designed to resolve:
- low signal
- information between lines
- Line Spacing / Flight Height: < 2 (Ideal = 1)
- Fly close to the ground with narrow line spacing
All industry surveys were flown at low altitudes (80 to 100 m above ground) with 100 to 200 m flight line spacing. Both fixed wing and helicopters were used.
Low Resolution vs. High Resolution: Scientific benefits of working with high resolution geophysical data are numerous, not the least of which is the wealth of information provided in the detail. The images below show the "before" and "after" of USGS magnetic survey with 1600 m line spacing, compared to the magnetic survey flown by UCore over Bokan Mtn with 100 m line spacing. The resolution provided in the UCore survey allows for detailed mapping of the host rocks, controlling structures, and mineralized system. The UCore data provides more than 10 times the resolution of the older USGS survey.
Magnetic anomaly map from a USGS survey with 1600 m line spacing. Magnetic anomaly map from UCore survey with 100 m line spacing. Image generated by USGS using UCore survey data. Multiple Sensors Collecting Data Concurrently: Another obvious benefit working with high resolution survey data is that all the industry surveys had multiple sensors on board collecting data simultaneously. For example, both the Bear Lodge and Bokan surveys include magnetic and gamma-ray data. The gamma-ray data is especially useful over exposed REE deposits as we can begin to understand the relationship between the radioelements (uranium [U], thorium [Th], and potassium [K]) and the concentrations of rare earth elements (REE) within the host and mineralized rocks. For the USGS Bokan study, our geophysicist is working closely with our mineralogist to understand the REE mineralogy as it relates to the uranium, thorium, and potassium minerals. Thru this process, connections are made that allow interpretation of the airborne geophysical data in the context of rare earth deposit setting and mineralization.
Bokan Mountain Deposit, Alaska
Bokan Mountain, located at the southern end of Prince of Wales Island, southeast Alaska, has been the site of past uranium mining and most recently is the focus for exploration of rare earth elements. Bokan Mountain is a peralkaline granite complex with associated dike vein systems that are enriched in a number of heavy rare earth elements (HREE).
An airborne geophysical survey, flown by Precision GeoSurveys and provided by UCore Rare Metals (http://ucore.com/), was recently flown over the Bokan deposit. The survey collected high resolution magnetic and gamma-ray spectrometry data along flight lines spaced 100-m apart. Bokan Mountain objectives are to:
- develop an understanding of the magnetic and radioelement properties of rare earth ore and ore hosts;
- analyze the relation between the rare earth element mineralogy and geophysical properties; and
- develop a regional geophysical characterization of peralkaline intrusion and possible geologic controls on mineralization.
Map of equivalent thorium (Th) (ppm) using data acquired from UCore Rare Metals. Elk Creek Deposit, Nebraska
The Elk Creek carbonatite, located in southeastern Nebraska, is host to niobium (Nb)-REE minerals and covered by approximately 200 m of sedimentary cover. An airborne geophysical survey that includes gravity gradiometry and magnetic data was recently flown and provides insight into the geophysical expression of a buried carbonatite. These data have been made available to the USGS through a non-disclosure agreement with NioCorp Developments Ltd. (formerly Quantum Rare Earth Developments Corporation), which allows USGS full access to digital flight line data and to publish figures, charts, maps, and interpretations of the data. Elk Creek objectives were to:
- develop an understanding of the magnetic and density properties of the Nb-rare earth ore and ore hosts at Elk Creek;
- develop models of the carbonatite through integration of physical property data collected on drill core and analyses of high resolution geophysical data; and
- develop a model that encompasses geophysical characterization of the Elk Creek carbonatite and possible geologic controls on mineralization.
Elk Creek Deposit, Nebraska vertical gravity gradient (Gdd) (left, filtered to emphasize effects of buried crystalline rocks) and magnetic anomaly (right, reduced-to-pole total-field) data plots. Red dots are borehole collar locations. Black polygon is the carbonatite margin. Bear Lodge Deposit, Wyoming
An airborne geophysical survey, provided by Rare Element Resources (http://www.rareelementresources.com/s/Home.asp), was recently flown over the Bear Lodge carbonatite deposit. The survey collected high resolution magnetic and gamma-ray spectrometry data along flight lines spaced 100-m apart. The map below shows the magnetic anomaly field over the Bear Lodge igneous complex, which hosts the rare earth–bearing carbonatite dikes within the Bull Hill area. Bear Lodge objectives were to:
- develop an understanding of the magnetic and radioelement properties of rare earth ore and ore hosts at Bear Lodge;
- analyze the relation between the rare earth element mineralogy and geophysical properties; and
- develop a regional geophysical characterization of alkaline intrusion, carbonatitic dikes and possible geologic controls on mineralization.
Bull Hill, location of the Bear Lodge Deposit, Wyoming. Magnetic data from Bear Lodge, Wyoming airborne geophysical survey. Map generated by USGS using data acquired from Rare Element Resources. References Cited
Barker, J.C., and Van Gosen, B.S., 2012, Alaska’s rare earth deposit and resource potential: Mining Engineering, v. 64, Issue 1, p. 20-32, http://me.smenet.org/abstract.cfm?preview=1&articleID=2502&page=20.
Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, D., 2010, The principal rare earth elements deposits of the United States—A summary of domestic deposits and a global perspective: U.S. Geological Survey Scientific Investigations Report 2010-5220, 96 p., https://doi.org/10.3133/sir20105220.
The use of firm, trade, and brand names is for identification purposes only and does not constitute endorsement by the U.S. government.
Return to Mineral Resources Program | Geology, Geophysics, and Geochemistry Science Center
- Science
Below are other science projects associated with this project.
Iron Oxide-Copper-Cobalt-Gold-Rare Earth Element Deposits of Southeast Missouri—From the Ore Deposit Scale to a Global Deposit Model
The project main objectives are to: 1) geologically, characterize the setting and origin of the iron-copper-cobalt-gold-rare earth element deposits, and advance the knowledge of rare earth element and Co potential within iron oxide-copper-gold (IOCG) deposits of southeast Missouri, and 2) geophysically delineate and characterize the subsurface Precambrian geology using existing ground and new...Continental Scale Geophysics — Integrated Approaches to Delineate Prospective Environments for Critical Metals
Regional geophysical data that are available over continental scales such as magnetic, gravity, and magnetotelluric data can provide a foundation towards identifying and understanding the footprints and deep plumbing systems underlying these important ore systems. Our project will use continental-scale geophysical data to map the locations of deep crustal and mantle structures that may act as...Geophysical and Geochemical Approaches to Evaluating Rare Earth Element (REE) Potential in the Southeastern U.S.
Rare-earth elements (REE) are an essential component of numerous advanced technology applications including high efficiency batteries, emerging energy technologies, and key defense systems. The goal of this study was to assist in the evaluation of the distribution of rare earth element deposits in the southeastern U.S., with a focus on sediment-hosted resources. - Publications
Below are publications associated with this project.
Geophysical expression of a buried niobium and rare earth element deposit: the Elk Creek carbonatite, Nebraska, USA
The lower Paleozoic Elk Creek carbonatite is a 6–8-km-diameter intrusive complex buried under 200 m of sedimentary rocks in southeastern Nebraska. It hosts the largest known niobium deposit in the U.S. and a rare earth element (REE) deposit. The carbonatite is composed of several lithologies, the relations of which are poorly understood. Niobium mineralization is most enriched within a magnetite bAuthorsBenjamin J. DrenthGeophysical interpretation of U, Th, and rare earth element mineralization of the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeast Alaska
A prospectivity map for rare earth element (REE) mineralization at the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeastern Alaska, was calculated from high-resolution airborne gamma-ray data. The map displays areas with similar radioelement concentrations as those over the Dotson REE-vein-dike system, which is characterized by moderately high %K, eU, and eTh (%K, perceAuthorsAnne E. McCafferty, Douglas B. Stoeser, Bradley S. Van Gosen - News
Below are news stories associated with this project.
- Partners
Below are partners associated with this project.