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Overview

potential rare earth deposits in Alaska locations
Estimated potential for rare earth element deposits in watersheds across the Bureau of Land Management Central Yukon Planning Area and surrounding regions, northern Alaska. Image from USGS Open-File Report 2015-1021. View full size image.

Alaska is dominated by a history of tectonic events that foster mobilization and concentration of a wide variety of mineral commodities that are critical to the US economy and are vital to national defense, renewable-energy, and emerging electronics technologies.

This project uses a recently developed, data-driven geographic information system (GIS)-based method to evaluate the potential of various mineral deposit types across the state of Alaska. The method systematically analyzes pre-existing, geospatially referenced datasets to generate a map, which provides a visual indication of the estimated potential (low, medium, high) and the certainty of that estimate (low, medium, high) for each watershed for a given group of mineral deposits or deposit types. Probabilities are calculated with set criteria based on lithology, geochemistry, and geophysical data. The datasets used include the USGS Alaska Geochemical Database, the Alaska Division of Geological and Geophysical Surveys web-based geochemical database, data from the recently released USGS geologic map of Alaska, the USGS Alaska Resource Data File, and airborne radiometric surveys from the National Uranium Resource Evaluation.

Examples of the various mineral deposit groups currently being evaluated by this method include placer gold, rare earth elements-thorium-niobium, sandstone uranium, platinum group elements-nickel-cobalt-chrome, copper-cobalt-silver-gallium-germanium, and tin-tungsten-molybdenum-tantalum-indium-fluorspar. The method is highly adaptable for the needs of diverse users, including scientific researchers, industry, land mangers such as the Bureau of Land Management and the State of Alaska, and Alaska Native corporations.

Examples of how this GIS analysis can be applied:

  1. Identification of areas with high mineral potential supported by abundant data.
  2. Identification of understudied and undersampled prospective areas.
  3. Topical investigations to improve current deposit models.
  4. Development and modification of resource evaluation techniques.
  5. Identification and recognition of new pathfinders and different types of data combinations linked to processes of ore genesis.
  6. Constraint or expansion of the footprint of known mineral belts.
  7. Discovery and definition of new mineral trends or belts.

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Pilot Study - Alaska Critical Minerals Cooperative

The current project is a continuation of a successful pilot study completed in 2015, which used the same scoring and mapping method for the Central Yukon Planning Area in central and northern Alaska. The scoring and mapping method was developed by the USGS in cooperation with the Alaska Division of Geological and Geophysical Surveys. The Bureau of Land Management requested that the study be conducted in the Central Yukon Planning Area to aid in their resource management planning. This pilot study evaluated potential for six different deposit types known to occur in specific rock types:

  1. Rare earth element deposits associated with alkali-rich intrusive rocks.
  2. Placer gold deposits associated with iron- and magnesium-rich, silica-poor igneous rocks like basalts.
  3. Platinum group element deposits associated with iron- and magnesium-rich, silica-poor igneous rocks like basalts.
  4. Copper deposits hosted in carbonate rocks.
  5. Uranium deposits in sandstone.
  6. Tin-tungsten-molybdenum-fluorspar deposits associated with some specialized granites.

Scoring System

The scoring system uses a number of parameters based on key characteristics specific to each deposit type. The key characteristics were chosen based on known occurrences of the mineral deposits around the world, known occurrences in Alaska, and previous research relating to the geologic processes responsible for the formation of these deposit types. The parameters are then scored and weighted for each of the different mineral deposit types. The confidence or certainty of the score is then calculated taking into consideration factors such as quantity of data and completeness of the datasets. Each deposit type has different parameters and different point values assigned to the parameters.

As an example, the scoring system for placer gold deposits uses five parameters: pan concentrate mineralogy, sediment geochemistry, rock type, geographical location, and whether the Alaska Resource Data File has any reports for the specific area mentioning placer gold as a keyword. Each parameter has a set number of possible points which allows for the parameters to weigh in differently to the total score. For example, pan concentrate data was assigned point values of up to 10, while the presence of plutonic rocks in the watershed only scored up to 3 points. In other words, if pan concentrate data for the area contains gold, there is a high probability of finding gold in the area; however, the presence of plutonic rocks in an area may often correlate with placer gold deposits, but not always, and thus weighs less on the overall score. After each parameter is assigned a score and a total score is calculated for the watershed, the certainty of the overall score is determined based on whether complete datasets are available for each of the parameters.

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Products

Jones, J.V., III, Karl, S.M., Labay, K.A., Shew, N.B., Granitto, M., Hayes, T.S., Mauk, J.L., Schmidt, J.M., Todd, E., Wang, B., Werdon, M.B., and Yager, D.B., 2015, GIS-based identification of areas with mineral resource potential for six selected deposit groups, Bureau of Land Management Central Yukon Planning Area, Alaska: U.S. Geological Survey Open-File Report 2015–1021, 78 p., 5 appendixes, 12 pls., https://dx.doi.org/10.3133/ofr20151021.

Karl, S.M., Jones, J.V., III, and Hayes, T.S., eds., 2016, GIS-based identification of areas that have resource potential for critical minerals in six selected groups of deposit types in Alaska: U.S. Geological Survey Open-File Report 2016–1191, 99 p., 5 appendixes, 12 plates, scale 1:10,500,000, https://dx.doi.org/10.3133/ofr20161191.

Karl, S.M., and Labay, K.A., Geospatial analysis identifies critical mineral-resource potential in Alaska: U.S. Geological Survey Fact Sheet 2017–3012, 4 p., https://doi.org/10.3133/fs20173012.

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