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#           Understanding PGE, Cr, Ni and Cu Potential in Ophiolitic Rocks in Alaska      

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      By Alaska Science Center      May 17, 2024    

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Ophiolites are sections of oceanic lithosphere that have been structurally emplaced onto continental crust. The ultramafic components of some ophiolites contain podiform chromitites, an important potential source of several strategic and critical minerals, including chromium and platinum group elements (PGE). Yet the tectonics and petrogenesis of several Alaskan ophiolites is poorly understood. This project endeavors to resolve the tectono-magmatic history of a suite of ophiolitic systems within Alaska, contributing towards an understanding of the primary conditions favorable for resource endowments.

**Return to ****Geology**

Alaska reflects a complex history of the accretion of disparate allochthonous terranes. Mafic-ultramafic complexes thought to represent variably complete sections of oceanic lithosphere, or ophiolites, are presumed to demarcate their paleo-boundaries. Several major ophiolite belts are recognized in interior/eastern Alaska, and occurrences of ore-grade PGEs are known from some, but not others. The origin, chronology, and tectonic context for most of these ophiolitic ore-magmatic systems remain poorly understood, as does the explanation for non-uniform PGE enrichments.

View Media Details

With few exceptions, most studies and mapping of Alaskan ophiolites were undertaken in the mid/late-20th century, primarily at the reconnaissance-level, and did not employ modern geochemical and geochronological techniques. As with analytical methods, the concept of ophiolite systems has also advanced significantly in the last few decades. Not all ophiolites are created equal, and the conceptual framework now exists to interpret the nature and melting conditions of source mantle, spreading rate/geometry, paleo-proximity to plumes/trenches/arcs, and availability of fluids during the formation of preserved oceanic lithosphere. These factors control the degree and composition of critical minerals in the ophiolite systems. Reinterpreting the origins of the mafic-ultramafic rocks in a modern framework will aid in the evaluation of critical mineral potential of Alaska. 

View Media Details

Initial efforts are focused on ophiolitic components of the Seventymile-Slide Mountain, Angayucham, Ruby, Livengood and Tozitna-Innoko terranes. Samples for this work were collected by legacy mapping and assessment efforts, as well as samples collected from fieldwork completed from 2013 to 2023. This project works to constrain the tectonic setting and petrogenesis of each system, contributing to a more comprehensive understanding of the mineral endowments in, and the assembly of, Alaska, including processes that localize and structurally translate its terrane components. 

### Study Area

### Contacts

#### Erin Todd, Ph.D.

##### Research Geologist

Alaska Science Center

etodd@usgs.gov

907-786-7441

### Explore Search

                      - Geology
                      - Geology
                      - Minerals
                      - Mafic
                      - Ultramafic
                      - Ophiolite
                      - mantle
                      - PGE
                      - Petrology
                      - igneous geochemistry
                      - radiogenic isotopes

View All **

link

May 22, 2018

####                 Tectonic and Metallogenic Evolution of the Yukon-Tanana Upland, Alaska              

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

link

May 22, 2018

####   Tectonic and Metallogenic Evolution of the Yukon-Tanana Upland, Alaska

Learn More

August 1, 2022

####                 Whole Rock Major and Trace Element Chemistry for Igneous and Metamorphic Rocks from the Yukon-Tanana Upland, Alaska              

Alaska Science Center

Sample Collection, Kanuti, Alaska

August 15, 2023

#### Sample Collection, Kanuti, Alaska

link

USGS researcher collecting samples in Kanuti, Alaska. The samples collected in this location were more resistant to weathering than the surrounding rock indicating a change in lithology.

Alaska Science Center

August 15, 2023

#### Sample Collection, Kanuti, Alaska

link

#### Sample Collection, Kanuti, Alaska

link

USGS researcher collecting samples in Kanuti, Alaska. The samples collected in this location were more resistant to weathering than the surrounding rock indicating a change in lithology.

Alaska Science Center

Recording observations on the outcrop of the Kanuti Ophiolite

August 11, 2023

#### Recording observations on the outcrop of the Kanuti Ophiolite

link

USGS researcher making observations and recording information on the outcrop of the Kanuti Ophiolite in Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

August 11, 2023

#### Recording observations on the outcrop of the Kanuti Ophiolite

link

#### Recording observations on the outcrop of the Kanuti Ophiolite

link

USGS researcher making observations and recording information on the outcrop of the Kanuti Ophiolite in Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

Leave no stone unturned

August 1, 2023

#### Leave no stone unturned

link

USGS researcher collecting one more sample while waiting for the helicopter in Kanuti, Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

August 1, 2023

#### Leave no stone unturned

link

#### Leave no stone unturned

link

USGS researcher collecting one more sample while waiting for the helicopter in Kanuti, Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

Variation of weathering on rock surface

July 26, 2020

#### Variation of weathering on rock surface

link

Variation of weathering and lichen growth on the rock surface reveals veins and segregated zones with different mineralogy. 

Alaska Science Center

July 26, 2020

#### Variation of weathering on rock surface

link

#### Variation of weathering on rock surface

link

Variation of weathering and lichen growth on the rock surface reveals veins and segregated zones with different mineralogy. 

Alaska Science Center

#### Colorado Mesa University

#### Louisiana State University

#### Michigan State University (MSU)

#### University of California, Santa Barbara

#### University of Maryland

#### University of South Carolina

#### University of Wisconsin

Ophiolites are sections of oceanic lithosphere that have been structurally emplaced onto continental crust. The ultramafic components of some ophiolites contain podiform chromitites, an important potential source of several strategic and critical minerals, including chromium and platinum group elements (PGE). Yet the tectonics and petrogenesis of several Alaskan ophiolites is poorly understood. This project endeavors to resolve the tectono-magmatic history of a suite of ophiolitic systems within Alaska, contributing towards an understanding of the primary conditions favorable for resource endowments.

**Return to ****Geology**

Alaska reflects a complex history of the accretion of disparate allochthonous terranes. Mafic-ultramafic complexes thought to represent variably complete sections of oceanic lithosphere, or ophiolites, are presumed to demarcate their paleo-boundaries. Several major ophiolite belts are recognized in interior/eastern Alaska, and occurrences of ore-grade PGEs are known from some, but not others. The origin, chronology, and tectonic context for most of these ophiolitic ore-magmatic systems remain poorly understood, as does the explanation for non-uniform PGE enrichments.

View Media Details

With few exceptions, most studies and mapping of Alaskan ophiolites were undertaken in the mid/late-20th century, primarily at the reconnaissance-level, and did not employ modern geochemical and geochronological techniques. As with analytical methods, the concept of ophiolite systems has also advanced significantly in the last few decades. Not all ophiolites are created equal, and the conceptual framework now exists to interpret the nature and melting conditions of source mantle, spreading rate/geometry, paleo-proximity to plumes/trenches/arcs, and availability of fluids during the formation of preserved oceanic lithosphere. These factors control the degree and composition of critical minerals in the ophiolite systems. Reinterpreting the origins of the mafic-ultramafic rocks in a modern framework will aid in the evaluation of critical mineral potential of Alaska. 

View Media Details

Initial efforts are focused on ophiolitic components of the Seventymile-Slide Mountain, Angayucham, Ruby, Livengood and Tozitna-Innoko terranes. Samples for this work were collected by legacy mapping and assessment efforts, as well as samples collected from fieldwork completed from 2013 to 2023. This project works to constrain the tectonic setting and petrogenesis of each system, contributing to a more comprehensive understanding of the mineral endowments in, and the assembly of, Alaska, including processes that localize and structurally translate its terrane components. 

### Study Area

### Contacts

#### Erin Todd, Ph.D.

##### Research Geologist

Alaska Science Center

etodd@usgs.gov

907-786-7441

### Explore Search

                      - Geology
                      - Geology
                      - Minerals
                      - Mafic
                      - Ultramafic
                      - Ophiolite
                      - mantle
                      - PGE
                      - Petrology
                      - igneous geochemistry
                      - radiogenic isotopes

View All **

link

May 22, 2018

####                 Tectonic and Metallogenic Evolution of the Yukon-Tanana Upland, Alaska              

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

link

May 22, 2018

####   Tectonic and Metallogenic Evolution of the Yukon-Tanana Upland, Alaska

Learn More

August 1, 2022

####                 Whole Rock Major and Trace Element Chemistry for Igneous and Metamorphic Rocks from the Yukon-Tanana Upland, Alaska              

Alaska Science Center

Sample Collection, Kanuti, Alaska

August 15, 2023

#### Sample Collection, Kanuti, Alaska

link

USGS researcher collecting samples in Kanuti, Alaska. The samples collected in this location were more resistant to weathering than the surrounding rock indicating a change in lithology.

Alaska Science Center

August 15, 2023

#### Sample Collection, Kanuti, Alaska

link

#### Sample Collection, Kanuti, Alaska

link

USGS researcher collecting samples in Kanuti, Alaska. The samples collected in this location were more resistant to weathering than the surrounding rock indicating a change in lithology.

Alaska Science Center

Recording observations on the outcrop of the Kanuti Ophiolite

August 11, 2023

#### Recording observations on the outcrop of the Kanuti Ophiolite

link

USGS researcher making observations and recording information on the outcrop of the Kanuti Ophiolite in Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

August 11, 2023

#### Recording observations on the outcrop of the Kanuti Ophiolite

link

#### Recording observations on the outcrop of the Kanuti Ophiolite

link

USGS researcher making observations and recording information on the outcrop of the Kanuti Ophiolite in Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

Leave no stone unturned

August 1, 2023

#### Leave no stone unturned

link

USGS researcher collecting one more sample while waiting for the helicopter in Kanuti, Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

August 1, 2023

#### Leave no stone unturned

link

#### Leave no stone unturned

link

USGS researcher collecting one more sample while waiting for the helicopter in Kanuti, Alaska. The Kanuti ophiolite is a mafic-ultramafic thrust sheet of probable Jurassic age, formerly considered to be the upper part of the Yukon-Koyukuk ophiolite (Angayucham terrane).

Alaska Science Center

Variation of weathering on rock surface

July 26, 2020

#### Variation of weathering on rock surface

link

Variation of weathering and lichen growth on the rock surface reveals veins and segregated zones with different mineralogy. 

Alaska Science Center

July 26, 2020

#### Variation of weathering on rock surface

link

#### Variation of weathering on rock surface

link

Variation of weathering and lichen growth on the rock surface reveals veins and segregated zones with different mineralogy. 

Alaska Science Center

#### Colorado Mesa University

#### Louisiana State University

#### Michigan State University (MSU)

#### University of California, Santa Barbara

#### University of Maryland

#### University of South Carolina

#### University of Wisconsin