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).
Critical Minerals in Alaska Placer Deposits and Southeast Alaska Mineral Systems
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By Alaska Science Center
May 23, 2024
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
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Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
| Project Goals |
| Identify critical mineral concentrations and volumes in selected placer deposits in each of the major mineral systems in Alaska (fig. 1). |
| Determine the enrichment of critical elements in placer tailings relative to that of unprocessed stream gravels. |
| Investigate critical element concentrations and host mineral phases in different size and density fractions of placer tailings to inform element concentration processes. |
| Research engineering technologies for efficient extraction of critical minerals from the tailings. |
| Identify the critical element host minerals and their chemical formulas; research metallurgical technologies for efficient and environmentally sensitive extraction of critical elements from their host minerals. |
| Evaluate practical and economic feasibility of extracting critical element byproducts and coproducts from legacy and active placer deposits, along with primary element products, using environmentally sustainable methods. |
| Delineate and incorporate ecological and societal benefit and risk factors in evaluations of critical mineral resource potential. |
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.
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Alaska locations of placer tailings sampling sites
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).
Uhler Creek
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.
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.
Cassiterite Creek
Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.
Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.
Dredge
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.
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.
Clear Creek
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.
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.
Chicken Creek
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.
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.
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
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
Sources/Usage: Public Domain. View Media Details
| Project Goals |
| Identify critical mineral concentrations and volumes in selected placer deposits in each of the major mineral systems in Alaska (fig. 1). |
| Determine the enrichment of critical elements in placer tailings relative to that of unprocessed stream gravels. |
| Investigate critical element concentrations and host mineral phases in different size and density fractions of placer tailings to inform element concentration processes. |
| Research engineering technologies for efficient extraction of critical minerals from the tailings. |
| Identify the critical element host minerals and their chemical formulas; research metallurgical technologies for efficient and environmentally sensitive extraction of critical elements from their host minerals. |
| Evaluate practical and economic feasibility of extracting critical element byproducts and coproducts from legacy and active placer deposits, along with primary element products, using environmentally sustainable methods. |
| Delineate and incorporate ecological and societal benefit and risk factors in evaluations of critical mineral resource potential. |
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.
Sources/Usage: Public Domain. 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.
Sources/Usage: Public Domain. View Media Details
Alaska locations of placer tailings sampling sites
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).
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).
Uhler Creek
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.
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.
Cassiterite Creek
Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.
Scientist sieving a sample of tin placer tailings in Cassiterite Creek on the western Seward Peninsula.
Dredge
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.
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.
Clear Creek
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.
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.
Chicken Creek
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.
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.