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Allen Andersen, PhD

Allen is a Research Geologist in the Spokane, WA field office for Geology, Minerals, Energy, and Geophysics Science Center. Allen works on projects related to economic geology.

Allen's broader interests include the genesis of magmatic-hydrothermal ore deposits, geochemistry applied to the assessment of critical mineral resources, fluid-rock interaction, and ore-forming processes of critical mineral deposits. More specifically, his wok focuses on the geology of rare earth element (REE) deposits, the behavior of REE in fluids and carbonatite magmas, and mineral resources associated with Paleogene magmatism across western North America. Allen also maintains interest in the formation of magmatic ore deposits enriched in platinum-group elements, chromium, nickel, copper, cobalt, titanium, and vanadium. Prior to joining the USGS, he spent more than six summers as a consulting geologist in the mineral exploration industry.

Current Projects

  • 2019–Present: Critical Elements in Carbonatites: From Exploration Targets to Element Distribution
  • 2018–Present: Critical Commodity Studies, Stillwater Complex, Montana
  • 2019–Present: Mineral Resource Assessment Training (Tungsten)

 

Education and Certifications

  • PhD, Geology, Washington State University

  • MSc Geology, Washington State University

  • BSc, Geology, Northwest Missouri State University

Science and Products

link
SEM image of carbonatite

Critical Elements in Carbonatites: From Exploration Targets to Element Distribution

Critical elements are essential to the modern economy and have potential supply chain disruptions, but compared to most base and precious metals, little work has been done in understanding ore-grade enrichments. Carbonatites are the primary source of the worlds light rare earth elements and niobium, and a potential source for heavy rare earths, scandium, tantalum, and thorium. Project objectives...
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center
link

Critical Elements in Carbonatites: From Exploration Targets to Element Distribution

Critical elements are essential to the modern economy and have potential supply chain disruptions, but compared to most base and precious metals, little work has been done in understanding ore-grade enrichments. Carbonatites are the primary source of the worlds light rare earth elements and niobium, and a potential source for heavy rare earths, scandium, tantalum, and thorium. Project objectives...
Learn More
link
USGS science for a changing world

Mineral Resource Assessment Training

The USGS Mineral Resources Program conducts mineral resource assessments and is training USGS scientists in how to conduct these assessments for future work. As a practical exercise, the scientists will conduct an assessment for tungsten in the U.S.
By
Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center
link

Mineral Resource Assessment Training

The USGS Mineral Resources Program conducts mineral resource assessments and is training USGS scientists in how to conduct these assessments for future work. As a practical exercise, the scientists will conduct an assessment for tungsten in the U.S.
Learn More
link
Image: Stillwater Mine

Critical commodity studies, Stillwater Complex, Montana and Duluth Complex, Minnesota

Scientific research can make our resource assessments of critical minerals more effective. This project focuses on the Stillwater Complex, Montana, which has rocks enriched in platinum-group elements (PGE), chromium, cobalt, and nickel. Project objectives are to update databases, evaluate new mapping techniques, document new styles of mineralization, and document and support research on the...
By
Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center
link

Critical commodity studies, Stillwater Complex, Montana and Duluth Complex, Minnesota

Scientific research can make our resource assessments of critical minerals more effective. This project focuses on the Stillwater Complex, Montana, which has rocks enriched in platinum-group elements (PGE), chromium, cobalt, and nickel. Project objectives are to update databases, evaluate new mapping techniques, document new styles of mineralization, and document and support research on the...
Learn More

Fluorite Samples from the Western United States - The Ronald G. Worl Collection

This dataset describes fluorite- and manganese-bearing samples collected and compiled by USGS Commodity Specialist, Ronald G. Worl during the 1970's. The dataset corresponds to a physical collection of fluorite- and manganese-bearing samples re-established under the National Geological and Geophysical Data Preservation Program and housed at the USGS building in Spokane Valley, Washington. The coll
By
Geology, Minerals, Energy, and Geophysics Science Center

Geochemical analyses of rock samples collected from the Judith Mountains and Crazy Mountains alkalic complexes, Montana

Geochemical data include major, minor and trace element results for 42 alkaline silicate igneous rock samples. Samples were collected from natural exposures/outcrops during field work in the Central Montana Alkaline Province (CMAP) during the summer of 2022. All samples were analyzed by the U.S. Geological Survey contract laboratory, SGS Labs. Major, minor, and trace elements were determined via w

By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Spatial data associated with tungsten skarn resource assessment of the Northern Rocky Mountains, Montana and Idaho

A mineral resource assessment was performed by the U.S. Geological Survey (USGS) to assess the potential of undiscovered skarn-hosted tungsten resources in the Northern Rocky Mountain region of eastern Idaho and western Montana. This region has seen moderate tungsten trioxide (WO3) production in the past from a variety of mineralization styles including skarn, vein and replacement, and wolframite-
By
Mineral Resources Program, Geology, Energy & Minerals Science Center, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center

Lithogeochemistry and images of selected drill core samples from the Mineral Hill alkaline complex, Wyoming

This data release contains analytical data and images for a suite of drill core samples from the Mineral Hill alkaline complex (MHAC), northeastern Wyoming. Geochemistry data include major and trace element analytical results for 103 alkaline igneous rock samples. Images include hand sample photographs of halved core and full thin section images captured in transmitted, plane-polarized and cross-p
By
Geology, Minerals, Energy, and Geophysics Science Center

Whole-rock geochemical data for the Bear Lodge alkaline complex, Wyoming: 2009 - 2013

This data release contains analytical data from a suite of rock samples collected within the Bear Lodge alkaline complex, northeast Wyoming, which hosts the Bear Lodge rare earth element (REE) deposit. Geochemistry data include major and trace element analytical results for 105 samples including alkaline igneous rocks, carbonatites, and weathered and oxidized samples. Samples were collected from s
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Lithogeochemistry of selected surface and drill core samples from the Chrome and Iron Mountain areas of the Stillwater Complex, Montana

Sulfide- and chromite-bearing samples of the Basal and Ultramafic series of the Stillwater Complex are known to contain elevated concentrations of chromium, nickel, copper, cobalt, gold, and platinum-group elements (PGE). Drill core and surface samples were collected from the Chrome and Iron Mountain areas for whole rock geochemical analysis, with specific interest in PGE, cobalt, and gold concent
By
Geology, Minerals, Energy, and Geophysics Science Center

TIMA-X Bright Phase Analysis of Platinum-Group Minerals in Selected Samples from the Chrome and Iron Mountain areas of the Stillwater Complex, Montana

Sulfide- and chromite-bearing samples of the Basal and Ultramafic series of the Stillwater Complex are known to contain elevated concentrations of platinum-group elements (PGE). Thin sections were prepared from drill core and surface samples from the Chrome and Iron Mountain areas. Core samples are from exploration drilling programs by AMAX in the 1960s and 1970s and Beartooth Platinum in 2004-200
By
Geology, Minerals, Energy, and Geophysics Science Center

GIS and Data Tables for Focus Areas for Potential Domestic Nonfuel Sources of Rare Earth Elements

In response to Executive Order 13817 of December 20, 2017, the U.S. Geological Survey (USGS) coordinated with the Bureau of Land Management (BLM) to identify 35 nonfuel minerals or mineral materials considered critical to the economic and national security of the United States (U.S.). Acquiring information on possible domestic sources of these critical minerals is the basis of the USGS Earth Mappi
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center, Earth Mapping Resources Initiative (Earth MRI)

Stable isotope constraints on the source of ore fluids for the Hicks Dome REE+Y-HFSE-fluorspar deposit

Hicks Dome is comprised of coarse crystalline Mississippi Valley Type deposits at shallow levels and an enigmatic, fine-grained fluorite, rare earth elements, Y, high field strength elements, Be, and Ba rich deposit at deeper levels. Phyllosilicates from a lamprophyre dike and a breccia from two Hicks Dome drill cores were sampled to resolve the fluid history of the entire deposit using light stab
Authors
Julia A. McIntosh, Craig A. Johnson, Allen K. Andersen, Albert H. Hofstra
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center

Tungsten resources of the northern Rocky Mountains, Montana and Idaho— A synthesis and quantitative assessment of skarn-hosted resources

Mineral resource assessments performed by the U.S. Geological Survey provide a synthesis of available information about the location of known and suspected mineral deposits. This study focuses on skarn-hosted tungsten resources in the northern Rocky Mountain region of east-central Idaho and western Montana which have seen moderate tungsten trioxide production in the past from a variety of minerali
Authors
Allen K. Andersen, Margaret A. Goldman, Mitchell M. Bennett, Connie L. Dicken, Philip J. Brown, Heather L. Parks
By
Geology, Minerals, Energy, and Geophysics Science Center

Focus areas for data acquisition for potential domestic resources of 13 critical minerals in the conterminous United States and Puerto Rico — Antimony, barite, beryllium, chromium, fluorspar, hafnium, helium, magnesium, manganese, potash, uranium, vanadiu

The Earth Mapping Resources Initiative (Earth MRI) is conducted in phases to identify areas for acquiring new geologic framework data to identify potential domestic resources of the 35 mineral materials designated as critical minerals for the United States. This report describes the data sources and summary results for 13 critical minerals evaluated in the conterminous United States and Puerto Ric
Authors
Jane M. Hammarstrom, Connie L. Dicken, Laurel G. Woodruff, Allen K. Andersen, Sean T. Brennan, Warren C. Day, Benjamin J. Drenth, Nora K. Foley, Susan Hall, Albert H. Hofstra, Anne E. McCafferty, Anjana K. Shah, David A. Ponce
By
Energy and Minerals Mission Area, Mineral Resources Program, Central Energy Resources Science Center, Geology, Energy & Minerals Science Center, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Earth Mapping Resources Initiative (Earth MRI)

Precious and base metal mineralization within the lower stratigraphy of the Stillwater Complex: New targets defined and old targets revisited

Group Ten Metals is exploring for base and precious metals within the Stillwater Complex, a 2.7 Ga layered mafic/ultramafic intrusion, host to the world-class Sibanye platinum group element (PGE) mines. Group Ten controls approximately 25 kilometers of strike length of prospective mafic and ultramafic rocks in the western portion of the Complex. The property includes multiple target types and indi
Authors
Craig Bow, Mike Ostenson, Justin Modroo, Allen K. Andersen
By
Geology, Minerals, Energy, and Geophysics Science Center

C–O stable isotope geochemistry and 40Ar/39Ar geochronology of the Bear Lodge carbonatite stockwork, Wyoming, USA

The carbonatite dike swarm and vein stockwork at the center of the Paleogene Bear Lodge alkaline complex (BLAC), Wyoming, USA, is host to diverse REE mineral assemblages that are largely a result of subsolidus modification and REE redistribution. Pseudomorphic replacement of primary burbankite by an assemblage of ancylite, strontianite, and barite is the result of interaction with late-stage hydro
Authors
Allen K. Andersen, Peter B. Larson, Michael A. Cosca
By
Geology, Minerals, Energy, and Geophysics Science Center

A preliminary study of older hot spring alteration in Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone Caldera, Wyoming

Erosion in the Grand Canyon of the Yellowstone River, Yellowstone Caldera (640 ka), Wyoming, has exposed a cross section of older hydrothermal alteration in the canyon walls. The altered outcrops of the post-collapse tuff of Sulphur Creek (480 ka) extend from the canyon rim to more than 300 m beneath it. The hydrothermal minerals are zoned, with an advanced argillic alteration consisting of an ass
Authors
Peter B. Larson, Allison Phillips, David A. John, Michael A. Cosca, Chad Pritchard, Allen K. Andersen, Jennifer Manion
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Non-USGS Publications**

Andersen, A.K., Clark, J.G., Larson, P.B., and Donovan, J.J., 2017. REE fractionation, mineral speciation,
and supergene enrichment of the Bear Lodge carbonatites, Wyoming, USA: Ore Geology Reviews.

v. 89, 780–807
Andersen, A.K., Clark, J.G., Larson, P.B., and Neill, O.K., 2016. Mineral chemistry and petrogenesis of a
HFSE(+HREE) occurrence, peripheral to carbonatites of the Bear Lodge alkaline complex, Wyoming: American Mineralogist, v. 101, 1604–1623.

**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

Science and Products

link
SEM image of carbonatite

Critical Elements in Carbonatites: From Exploration Targets to Element Distribution

Critical elements are essential to the modern economy and have potential supply chain disruptions, but compared to most base and precious metals, little work has been done in understanding ore-grade enrichments. Carbonatites are the primary source of the worlds light rare earth elements and niobium, and a potential source for heavy rare earths, scandium, tantalum, and thorium. Project objectives...
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center
link

Critical Elements in Carbonatites: From Exploration Targets to Element Distribution

Critical elements are essential to the modern economy and have potential supply chain disruptions, but compared to most base and precious metals, little work has been done in understanding ore-grade enrichments. Carbonatites are the primary source of the worlds light rare earth elements and niobium, and a potential source for heavy rare earths, scandium, tantalum, and thorium. Project objectives...
Learn More
link
USGS science for a changing world

Mineral Resource Assessment Training

The USGS Mineral Resources Program conducts mineral resource assessments and is training USGS scientists in how to conduct these assessments for future work. As a practical exercise, the scientists will conduct an assessment for tungsten in the U.S.
By
Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center
link

Mineral Resource Assessment Training

The USGS Mineral Resources Program conducts mineral resource assessments and is training USGS scientists in how to conduct these assessments for future work. As a practical exercise, the scientists will conduct an assessment for tungsten in the U.S.
Learn More
link
Image: Stillwater Mine

Critical commodity studies, Stillwater Complex, Montana and Duluth Complex, Minnesota

Scientific research can make our resource assessments of critical minerals more effective. This project focuses on the Stillwater Complex, Montana, which has rocks enriched in platinum-group elements (PGE), chromium, cobalt, and nickel. Project objectives are to update databases, evaluate new mapping techniques, document new styles of mineralization, and document and support research on the...
By
Mineral Resources Program, Geology, Minerals, Energy, and Geophysics Science Center
link

Critical commodity studies, Stillwater Complex, Montana and Duluth Complex, Minnesota

Scientific research can make our resource assessments of critical minerals more effective. This project focuses on the Stillwater Complex, Montana, which has rocks enriched in platinum-group elements (PGE), chromium, cobalt, and nickel. Project objectives are to update databases, evaluate new mapping techniques, document new styles of mineralization, and document and support research on the...
Learn More

Fluorite Samples from the Western United States - The Ronald G. Worl Collection

This dataset describes fluorite- and manganese-bearing samples collected and compiled by USGS Commodity Specialist, Ronald G. Worl during the 1970's. The dataset corresponds to a physical collection of fluorite- and manganese-bearing samples re-established under the National Geological and Geophysical Data Preservation Program and housed at the USGS building in Spokane Valley, Washington. The coll
By
Geology, Minerals, Energy, and Geophysics Science Center

Geochemical analyses of rock samples collected from the Judith Mountains and Crazy Mountains alkalic complexes, Montana

Geochemical data include major, minor and trace element results for 42 alkaline silicate igneous rock samples. Samples were collected from natural exposures/outcrops during field work in the Central Montana Alkaline Province (CMAP) during the summer of 2022. All samples were analyzed by the U.S. Geological Survey contract laboratory, SGS Labs. Major, minor, and trace elements were determined via w

By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Spatial data associated with tungsten skarn resource assessment of the Northern Rocky Mountains, Montana and Idaho

A mineral resource assessment was performed by the U.S. Geological Survey (USGS) to assess the potential of undiscovered skarn-hosted tungsten resources in the Northern Rocky Mountain region of eastern Idaho and western Montana. This region has seen moderate tungsten trioxide (WO3) production in the past from a variety of mineralization styles including skarn, vein and replacement, and wolframite-
By
Mineral Resources Program, Geology, Energy & Minerals Science Center, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center

Lithogeochemistry and images of selected drill core samples from the Mineral Hill alkaline complex, Wyoming

This data release contains analytical data and images for a suite of drill core samples from the Mineral Hill alkaline complex (MHAC), northeastern Wyoming. Geochemistry data include major and trace element analytical results for 103 alkaline igneous rock samples. Images include hand sample photographs of halved core and full thin section images captured in transmitted, plane-polarized and cross-p
By
Geology, Minerals, Energy, and Geophysics Science Center

Whole-rock geochemical data for the Bear Lodge alkaline complex, Wyoming: 2009 - 2013

This data release contains analytical data from a suite of rock samples collected within the Bear Lodge alkaline complex, northeast Wyoming, which hosts the Bear Lodge rare earth element (REE) deposit. Geochemistry data include major and trace element analytical results for 105 samples including alkaline igneous rocks, carbonatites, and weathered and oxidized samples. Samples were collected from s
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Lithogeochemistry of selected surface and drill core samples from the Chrome and Iron Mountain areas of the Stillwater Complex, Montana

Sulfide- and chromite-bearing samples of the Basal and Ultramafic series of the Stillwater Complex are known to contain elevated concentrations of chromium, nickel, copper, cobalt, gold, and platinum-group elements (PGE). Drill core and surface samples were collected from the Chrome and Iron Mountain areas for whole rock geochemical analysis, with specific interest in PGE, cobalt, and gold concent
By
Geology, Minerals, Energy, and Geophysics Science Center

TIMA-X Bright Phase Analysis of Platinum-Group Minerals in Selected Samples from the Chrome and Iron Mountain areas of the Stillwater Complex, Montana

Sulfide- and chromite-bearing samples of the Basal and Ultramafic series of the Stillwater Complex are known to contain elevated concentrations of platinum-group elements (PGE). Thin sections were prepared from drill core and surface samples from the Chrome and Iron Mountain areas. Core samples are from exploration drilling programs by AMAX in the 1960s and 1970s and Beartooth Platinum in 2004-200
By
Geology, Minerals, Energy, and Geophysics Science Center

GIS and Data Tables for Focus Areas for Potential Domestic Nonfuel Sources of Rare Earth Elements

In response to Executive Order 13817 of December 20, 2017, the U.S. Geological Survey (USGS) coordinated with the Bureau of Land Management (BLM) to identify 35 nonfuel minerals or mineral materials considered critical to the economic and national security of the United States (U.S.). Acquiring information on possible domestic sources of these critical minerals is the basis of the USGS Earth Mappi
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center, Earth Mapping Resources Initiative (Earth MRI)

Stable isotope constraints on the source of ore fluids for the Hicks Dome REE+Y-HFSE-fluorspar deposit

Hicks Dome is comprised of coarse crystalline Mississippi Valley Type deposits at shallow levels and an enigmatic, fine-grained fluorite, rare earth elements, Y, high field strength elements, Be, and Ba rich deposit at deeper levels. Phyllosilicates from a lamprophyre dike and a breccia from two Hicks Dome drill cores were sampled to resolve the fluid history of the entire deposit using light stab
Authors
Julia A. McIntosh, Craig A. Johnson, Allen K. Andersen, Albert H. Hofstra
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center

Tungsten resources of the northern Rocky Mountains, Montana and Idaho— A synthesis and quantitative assessment of skarn-hosted resources

Mineral resource assessments performed by the U.S. Geological Survey provide a synthesis of available information about the location of known and suspected mineral deposits. This study focuses on skarn-hosted tungsten resources in the northern Rocky Mountain region of east-central Idaho and western Montana which have seen moderate tungsten trioxide production in the past from a variety of minerali
Authors
Allen K. Andersen, Margaret A. Goldman, Mitchell M. Bennett, Connie L. Dicken, Philip J. Brown, Heather L. Parks
By
Geology, Minerals, Energy, and Geophysics Science Center

Focus areas for data acquisition for potential domestic resources of 13 critical minerals in the conterminous United States and Puerto Rico — Antimony, barite, beryllium, chromium, fluorspar, hafnium, helium, magnesium, manganese, potash, uranium, vanadiu

The Earth Mapping Resources Initiative (Earth MRI) is conducted in phases to identify areas for acquiring new geologic framework data to identify potential domestic resources of the 35 mineral materials designated as critical minerals for the United States. This report describes the data sources and summary results for 13 critical minerals evaluated in the conterminous United States and Puerto Ric
Authors
Jane M. Hammarstrom, Connie L. Dicken, Laurel G. Woodruff, Allen K. Andersen, Sean T. Brennan, Warren C. Day, Benjamin J. Drenth, Nora K. Foley, Susan Hall, Albert H. Hofstra, Anne E. McCafferty, Anjana K. Shah, David A. Ponce
By
Energy and Minerals Mission Area, Mineral Resources Program, Central Energy Resources Science Center, Geology, Energy & Minerals Science Center, Geology, Geophysics, and Geochemistry Science Center, Geology, Minerals, Energy, and Geophysics Science Center, Earth Mapping Resources Initiative (Earth MRI)

Precious and base metal mineralization within the lower stratigraphy of the Stillwater Complex: New targets defined and old targets revisited

Group Ten Metals is exploring for base and precious metals within the Stillwater Complex, a 2.7 Ga layered mafic/ultramafic intrusion, host to the world-class Sibanye platinum group element (PGE) mines. Group Ten controls approximately 25 kilometers of strike length of prospective mafic and ultramafic rocks in the western portion of the Complex. The property includes multiple target types and indi
Authors
Craig Bow, Mike Ostenson, Justin Modroo, Allen K. Andersen
By
Geology, Minerals, Energy, and Geophysics Science Center

C–O stable isotope geochemistry and 40Ar/39Ar geochronology of the Bear Lodge carbonatite stockwork, Wyoming, USA

The carbonatite dike swarm and vein stockwork at the center of the Paleogene Bear Lodge alkaline complex (BLAC), Wyoming, USA, is host to diverse REE mineral assemblages that are largely a result of subsolidus modification and REE redistribution. Pseudomorphic replacement of primary burbankite by an assemblage of ancylite, strontianite, and barite is the result of interaction with late-stage hydro
Authors
Allen K. Andersen, Peter B. Larson, Michael A. Cosca
By
Geology, Minerals, Energy, and Geophysics Science Center

A preliminary study of older hot spring alteration in Sevenmile Hole, Grand Canyon of the Yellowstone River, Yellowstone Caldera, Wyoming

Erosion in the Grand Canyon of the Yellowstone River, Yellowstone Caldera (640 ka), Wyoming, has exposed a cross section of older hydrothermal alteration in the canyon walls. The altered outcrops of the post-collapse tuff of Sulphur Creek (480 ka) extend from the canyon rim to more than 300 m beneath it. The hydrothermal minerals are zoned, with an advanced argillic alteration consisting of an ass
Authors
Peter B. Larson, Allison Phillips, David A. John, Michael A. Cosca, Chad Pritchard, Allen K. Andersen, Jennifer Manion
By
Mineral Resources Program, Geology, Geophysics, and Geochemistry Science Center

Non-USGS Publications**

Andersen, A.K., Clark, J.G., Larson, P.B., and Donovan, J.J., 2017. REE fractionation, mineral speciation,
and supergene enrichment of the Bear Lodge carbonatites, Wyoming, USA: Ore Geology Reviews.

v. 89, 780–807
Andersen, A.K., Clark, J.G., Larson, P.B., and Neill, O.K., 2016. Mineral chemistry and petrogenesis of a
HFSE(+HREE) occurrence, peripheral to carbonatites of the Bear Lodge alkaline complex, Wyoming: American Mineralogist, v. 101, 1604–1623.

**Disclaimer: The views expressed in Non-USGS publications are those of the author and do not represent the views of the USGS, Department of the Interior, or the U.S. Government.

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