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#           Critical Minerals in Alaska Placer Deposits and Southeast Alaska Mineral Systems      

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      By Alaska Science Center      May 23, 2024    

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Critical minerals have been identified in most Alaskan placers, yet little is known about the concentration of these phases. Historic and active placer mines have typically produced gold and are widespread across Alaska. Activity in the placer districts has resulted in gravel piles and sluice tailings that are products of   gold mining. Gold has been the traditional target of placer mining; however, mechanical and physical sorting of mineral phases known to host important critical minerals such as tungsten and tin occurs through similar processes as gold concentration. Knowledge of the degree to which commodities other than gold have been concentrated in placers is lacking due to historic interest, almost exclusively, in gold for economic reasons

**Return to****Geology****>>****AK Mine Waste**

 

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This project builds on completed geospatial prospectivity analyses for critical minerals and gold in Alaska (Karl et al., 2016; 2021). The preliminary prospectivity analyses provide additional constraints on selecting specific placer deposits to sample and inventory critical minerals present in a variety of mineral systems. Deposits associated with different mineral systems may have distinct geochemical and critical mineral enrichments. Sampling and inventorying placers that are related to diverse metallogenic sources provides a more complete understanding and ultimately predictive capability for additional resources across the state.

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Beginning in 2022, eight bulk samples of placer tailings were collected from the historic Flat district in southwest Alaska. Flat was the third largest placer gold producer in Alaska in the early 1900’s, following the Fairbanks and Nome districts. The drainages sampled have source regions that include known mineral occurrences with enrichments in tin, tungsten and arsenic. Chemical and mineralogical analysis of multiple size fractions will identify host minerals including the elemental compositions to better characterize the distribution of critical minerals in the placers. 

Preliminary results confirmed sample collection protocols.  Twenty-three samples were collected during the 2023 field season from many of the main mineral systems that contain different suites of critical minerals around the state (fig. 1). The remaining target areas will be sampled in 2024. The samples collected in 2023 will be processed according to protocols developed in the pilot study. 

View Media Details

### Study Area

### Contacts

#### Susan Karl

##### Research Geologist

Alaska Science Center

skarl@usgs.gov

907-786-7428

### Explore Search

                      - Geology
                      - Minerals
                      - Earth Mapping Resources Initiative (Earth MRI)
                      - Mine Waste
                      - critical minerals
                      - critical elements
                      - Placer
                      - mineral resource potential
                      -  Alaska

View All **

Alaska locations of placer tailings sampling sites 

September 5, 2023

#### Alaska locations of placer tailings sampling sites 

link

Map showing locations of placer mines in the Alaska Resource Data File (ARDF, red crosses), primary mineral districts that contain targeted critical minerals (black boxes) and locations that were sampled by the USGS in 2022 and 2023 (yellow stars).

Alaska Science Center

September 5, 2023

#### Alaska locations of placer tailings sampling sites 

link

#### Alaska locations of placer tailings sampling sites 

link

Map showing locations of placer mines in the Alaska Resource Data File (ARDF, red crosses), primary mineral districts that contain targeted critical minerals (black boxes) and locations that were sampled by the USGS in 2022 and 2023 (yellow stars).

Alaska Science Center

Uhler Creek

August 24, 2023

#### Uhler Creek

link

Scientist sieving a sample of gold placer tailings to analyze for critical mineral contents in Uhler Creek, a tributary to the South Fork of the Forty Mile River in east central Alaska.

Alaska Science Center, Alaska Science Center

August 24, 2023

#### Uhler Creek

link

#### Uhler Creek

link

Scientist sieving a sample of gold placer tailings to analyze for critical mineral contents in Uhler Creek, a tributary to the South Fork of the Forty Mile River in east central Alaska.

Alaska Science Center, Alaska Science Center

Cassiterite Creek

July 23, 2023

#### Cassiterite Creek

link

Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.

Alaska Science Center, Alaska Science Center

July 23, 2023

#### Cassiterite Creek

link

#### Cassiterite Creek

link

Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.

Alaska Science Center, Alaska Science Center

Dredge 

July 12, 2023

#### Dredge 

link

Historic dredge and large volume of gold placer tailings that contain platinum group and chromium critical minerals on the Salmon River near Goodnews Bay, Alaska. Dragline-sluice tailings are in the foreground, stacked dredge tailings are in the background near the dredge.

Alaska Science Center

July 12, 2023

#### Dredge 

link

#### Dredge 

link

Historic dredge and large volume of gold placer tailings that contain platinum group and chromium critical minerals on the Salmon River near Goodnews Bay, Alaska. Dragline-sluice tailings are in the foreground, stacked dredge tailings are in the background near the dredge.

Alaska Science Center

Clear Creek

June 21, 2023

#### Clear Creek

link

Scientists collecting a 1/5 yard composite sample in blue 5-gallon buckets from gold placer tailings to analyze for critical mineral contents in Clear Creek, in the Zane Hills north central Alaska.

Alaska Science Center, Alaska Science Center

June 21, 2023

#### Clear Creek

link

#### Clear Creek

link

Scientists collecting a 1/5 yard composite sample in blue 5-gallon buckets from gold placer tailings to analyze for critical mineral contents in Clear Creek, in the Zane Hills north central Alaska.

Alaska Science Center, Alaska Science Center

Chicken Creek

August 24, 2022

#### Chicken Creek

link

Scientist checking a gold pan for gold and critical minerals in placer tailings on lower Chicken Creek near Flat, Alaska, in the Kuskokwim Mountains. A sample was collected from legacy gold placer tailings at this site and 7 others in the Flat mining district to determine the critical mineral contents of tailings from which only gold has been removed.

Alaska Science Center, Alaska Science Center

August 24, 2022

#### Chicken Creek

link

#### Chicken Creek

link

Scientist checking a gold pan for gold and critical minerals in placer tailings on lower Chicken Creek near Flat, Alaska, in the Kuskokwim Mountains. A sample was collected from legacy gold placer tailings at this site and 7 others in the Flat mining district to determine the critical mineral contents of tailings from which only gold has been removed.

Alaska Science Center, Alaska Science Center

June 29, 2021

####                 GIS-based identification of areas that have resource potential for lode gold in Alaska              

Ecosystems Mission Area, Energy and Minerals Mission Area, Mineral Resources Program, Alaska Science Center, Geology, Geophysics, and Geochemistry Science Center

August 16, 2018

####                 Multi-Resource Analysis—Methodology and synthesis              

Science and Decisions Center

November 16, 2016

####                 GIS-based identification of areas that have resource potential for critical minerals in six selected groups of deposit types in Alaska              

Alaska Science Center

Critical minerals have been identified in most Alaskan placers, yet little is known about the concentration of these phases. Historic and active placer mines have typically produced gold and are widespread across Alaska. Activity in the placer districts has resulted in gravel piles and sluice tailings that are products of   gold mining. Gold has been the traditional target of placer mining; however, mechanical and physical sorting of mineral phases known to host important critical minerals such as tungsten and tin occurs through similar processes as gold concentration. Knowledge of the degree to which commodities other than gold have been concentrated in placers is lacking due to historic interest, almost exclusively, in gold for economic reasons

**Return to****Geology****>>****AK Mine Waste**

 

View Media Details

View Media Details

View Media Details

 

 

This project builds on completed geospatial prospectivity analyses for critical minerals and gold in Alaska (Karl et al., 2016; 2021). The preliminary prospectivity analyses provide additional constraints on selecting specific placer deposits to sample and inventory critical minerals present in a variety of mineral systems. Deposits associated with different mineral systems may have distinct geochemical and critical mineral enrichments. Sampling and inventorying placers that are related to diverse metallogenic sources provides a more complete understanding and ultimately predictive capability for additional resources across the state.

View Media Details

Beginning in 2022, eight bulk samples of placer tailings were collected from the historic Flat district in southwest Alaska. Flat was the third largest placer gold producer in Alaska in the early 1900’s, following the Fairbanks and Nome districts. The drainages sampled have source regions that include known mineral occurrences with enrichments in tin, tungsten and arsenic. Chemical and mineralogical analysis of multiple size fractions will identify host minerals including the elemental compositions to better characterize the distribution of critical minerals in the placers. 

Preliminary results confirmed sample collection protocols.  Twenty-three samples were collected during the 2023 field season from many of the main mineral systems that contain different suites of critical minerals around the state (fig. 1). The remaining target areas will be sampled in 2024. The samples collected in 2023 will be processed according to protocols developed in the pilot study. 

View Media Details

### Study Area

### Contacts

#### Susan Karl

##### Research Geologist

Alaska Science Center

skarl@usgs.gov

907-786-7428

### Explore Search

                      - Geology
                      - Minerals
                      - Earth Mapping Resources Initiative (Earth MRI)
                      - Mine Waste
                      - critical minerals
                      - critical elements
                      - Placer
                      - mineral resource potential
                      -  Alaska

View All **

Alaska locations of placer tailings sampling sites 

September 5, 2023

#### Alaska locations of placer tailings sampling sites 

link

Map showing locations of placer mines in the Alaska Resource Data File (ARDF, red crosses), primary mineral districts that contain targeted critical minerals (black boxes) and locations that were sampled by the USGS in 2022 and 2023 (yellow stars).

Alaska Science Center

September 5, 2023

#### Alaska locations of placer tailings sampling sites 

link

#### Alaska locations of placer tailings sampling sites 

link

Map showing locations of placer mines in the Alaska Resource Data File (ARDF, red crosses), primary mineral districts that contain targeted critical minerals (black boxes) and locations that were sampled by the USGS in 2022 and 2023 (yellow stars).

Alaska Science Center

Uhler Creek

August 24, 2023

#### Uhler Creek

link

Scientist sieving a sample of gold placer tailings to analyze for critical mineral contents in Uhler Creek, a tributary to the South Fork of the Forty Mile River in east central Alaska.

Alaska Science Center, Alaska Science Center

August 24, 2023

#### Uhler Creek

link

#### Uhler Creek

link

Scientist sieving a sample of gold placer tailings to analyze for critical mineral contents in Uhler Creek, a tributary to the South Fork of the Forty Mile River in east central Alaska.

Alaska Science Center, Alaska Science Center

Cassiterite Creek

July 23, 2023

#### Cassiterite Creek

link

Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.

Alaska Science Center, Alaska Science Center

July 23, 2023

#### Cassiterite Creek

link

#### Cassiterite Creek

link

Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.

Alaska Science Center, Alaska Science Center

Dredge 

July 12, 2023

#### Dredge 

link

Historic dredge and large volume of gold placer tailings that contain platinum group and chromium critical minerals on the Salmon River near Goodnews Bay, Alaska. Dragline-sluice tailings are in the foreground, stacked dredge tailings are in the background near the dredge.

Alaska Science Center

July 12, 2023

#### Dredge 

link

#### Dredge 

link

Historic dredge and large volume of gold placer tailings that contain platinum group and chromium critical minerals on the Salmon River near Goodnews Bay, Alaska. Dragline-sluice tailings are in the foreground, stacked dredge tailings are in the background near the dredge.

Alaska Science Center

Clear Creek

June 21, 2023

#### Clear Creek

link

Scientists collecting a 1/5 yard composite sample in blue 5-gallon buckets from gold placer tailings to analyze for critical mineral contents in Clear Creek, in the Zane Hills north central Alaska.

Alaska Science Center, Alaska Science Center

June 21, 2023

#### Clear Creek

link

#### Clear Creek

link

Scientists collecting a 1/5 yard composite sample in blue 5-gallon buckets from gold placer tailings to analyze for critical mineral contents in Clear Creek, in the Zane Hills north central Alaska.

Alaska Science Center, Alaska Science Center

Chicken Creek

August 24, 2022

#### Chicken Creek

link

Scientist checking a gold pan for gold and critical minerals in placer tailings on lower Chicken Creek near Flat, Alaska, in the Kuskokwim Mountains. A sample was collected from legacy gold placer tailings at this site and 7 others in the Flat mining district to determine the critical mineral contents of tailings from which only gold has been removed.

Alaska Science Center, Alaska Science Center

August 24, 2022

#### Chicken Creek

link

#### Chicken Creek

link

Scientist checking a gold pan for gold and critical minerals in placer tailings on lower Chicken Creek near Flat, Alaska, in the Kuskokwim Mountains. A sample was collected from legacy gold placer tailings at this site and 7 others in the Flat mining district to determine the critical mineral contents of tailings from which only gold has been removed.

Alaska Science Center, Alaska Science Center

June 29, 2021

####                 GIS-based identification of areas that have resource potential for lode gold in Alaska              

Ecosystems Mission Area, Energy and Minerals Mission Area, Mineral Resources Program, Alaska Science Center, Geology, Geophysics, and Geochemistry Science Center

August 16, 2018

####                 Multi-Resource Analysis—Methodology and synthesis              

Science and Decisions Center

November 16, 2016

####                 GIS-based identification of areas that have resource potential for critical minerals in six selected groups of deposit types in Alaska              

Alaska Science Center