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Alaska is considered one of the premier locations in the world for mineral exploration and for discovery of world-class mineral resources. However, geologic mapping and exploration are hindered by Alaska’s vast size, remoteness, and rugged terrain. Hyperspectral surveying is one method that can be used to rapidly acquire data about the distributions of surficial materials, including different types of bedrock and ground cover. The USGS conducted a pilot project in the state of Alaska, USA, to test the effectiveness of using imaging spectroscopy (hyperspectral remote sensing) to characterize surficial materials, geology, and potential mineral resources for selected areas of interest (AOIs).
Our research objectives were to:
The goal of the project was to define the geologic footprint of select deposits using imaging spectroscopy, and regionally extrapolate this knowledge to areas not well characterized. It is expected that the synthesis of results from this multi-disciplinary project will enhance our understanding of the regional geology and be used to develop a predictive exploration model for the identification of base and precious metal-bearing deposits in Alaska and similar remote regions of the world.
An airborne survey to collect hyperspectral remote sensing data covering several areas of interest in Alaska was performed by the USGS during the summer of 2014. The areas of interest included known large tonnage metallic mineral resources and associated broad alteration footprints. Supporting field work including field spectroscopy, geologic field investigations, and mineral mapping, was conducted to aid in the calibration and interpretation of remotely sensed data.
Hyperspectral data were collected at multiple scales in the Nabesna area of interest. The scales ranged from regional, at 6-meter resolution covering hundreds of kilometers, to outcrop-scale at 30-centimeter resolution, to hand sample scale, at 500-micrometer resolution. This work was conducted in collaboration with the Alaska Department of Natural Resources Division of Geological and Geophysical Surveys, University of Alaska Fairbanks, and National Park Service. Preliminary examination of surface mineral maps show patterns of mineralogy consistent with those predicted from existing geologic maps and descriptions of the porphyry deposits in the region.
Cole, C.J., Johnson, M.R., and Graham, G.E., 2014, Advanced Land Observing Satellite (ALOS) Phased Array Type L-Band Synthetic Aperture Radar (PALSAR) mosaic for the Kahiltna terrane, Alaska, 2007–2010: U.S. Geological Survey Scientific Investigations Map, 1 sheet, scale 1:1,000,000, https://doi.org/10.3133/sim3323.
Graham, G.E., Kokaly, R.F., Kelley, K.D., Hoefen, T.M., Johnson, M.R., and Hubbard, B.E., 2018, Application of Imaging Spectroscopy for Mineral Exploration in Alaska: A Study over Porphyry Cu Deposits in the Eastern Alaska Range: Economic Geology, 113(2), p. 489-510, doi:10.5382/econgeo.2018.4559.
Johnson, M.R., Graham, G.E., Hubbard, B.E., and Benzel, W.M., 2015, Geospatial compilation of results from field sample collection in support of mineral resource investigations, Western Alaska Range, Alaska, July 2013: U.S. Geological Survey Data Series 943, 12 p., https://doi.org/10.3133/ds943.
Kokaly, R.F., Graham, G.E., Hoefen, T.M., Kelley, K.D., Johnson, M.R., and Hubbard, B.E., Hyperspectral surveying for mineral resources in Alaska: U.S. Geological Survey Fact Sheet 2016-3029, 2 p., https://doi.org/10.3133/fs20163029.
Kokaly, R.F., and Skidmore, A.K., 2015, Plant phenolics and absorption features in vegetation reflectance spectra near 1.66 μm: International Journal of Applied Earth Observation and Geoinformation, 43, p. 55-63, doi:10.1016/j.jag.2015.01.010.
Graham, G.E., Johnson, M.R., Kelley, K.D., Kokaly, R.F., and Hoefen, T.M., 2017, Whole rock, soil, sediment, x-ray diffraction, and electron microprobe analyses of samples from the Orange Hill-Bond Creek area, Nabesna Quadrangle, Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/F78051K1.
Kokaly, R.F., Hoefen, T.M., King, T.V.V., and Johnson, M.R., 2017, Airborne imaging spectrometer data collected for characterizing mineral resources near Nabesna, Alaska, 2014: U.S. Geological Survey data release, https://doi.org/10.5066/F7DN435W.
Kokaly, R.F., Johnson, M.R., Graham, G.E., Hoefen, T.M, Kelley, K.D., and Hubbard, B.E., 2018, Imaging spectrometer reflectance data, mineral predominance map, and white mica wavelength position map, Nabesna Quadrangle, Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/F7NV9H6F.
Cristobal, J., Buchhorn, M., Kokaly, R.F., Prakash, A., Werdon, M., and Graham, P., 2016, Alaska’s New Field-Based and Airborne Hyperspectral Imaging Facility Supporting Mineral Exploration and Mapping: 2016 Alaska Miners Association Biennial Convention, Fairbanks, AK, April 4–9, 2016.
Graham, G.E., Kokaly, R., Hoefen, T., Kelley, K., Johnson, M., Hubbard, B., and Goldfarb, R., 2015, USGS Hyperspectral Survey Pilot Study – An Update: Alaska Miners Association Annual Meeting, Anchorage, AK, November 3-5, 2015.
Graham, G.E., Kelley, K.D., Holm-Denoma, C.S., Ayuso, R.A., Kokaly, R.F., Hoefen, T.M., and Selby, D., 2016, Geochronology of Early Cretaceous porphyry Cu deposits in Eastern Alaska: 35th International Geological Congress, Capetown, South Africa, August 27 - September 4, 2016.
Kokaly, R.F., 2015, Expanding the frontiers of HSI for vegetation and mineral resources: ENVI Analytics Symposium, Boulder, CO, August 25-26, 2015.
Kokaly, R.F., Graham, G.E., Hoefen, T.M., Kelley, K.D., Johnson, M.R., Hubbard, B.E., Goldfarb, R.J., Buchhorn, M., and Prakash, A., 2016, Exploration applications of laboratory, field, and airborne imaging spectrometer data collected from the Orange Hill Porphyry Cu deposit, east-central Alaska, USA, 35th International Geological Congress, Cape Town, South Africa, August 27 – September 4, 2016.
Kokaly, R.F., Hoefen, T.M., Graham, G.E., Kelley, K.D., Johnson, M.R., Cole, C.J., Hubbard, B.E., and Goldfarb, R.J., 2014, USGS Hyperspectral surveys – methodology and preliminary data: Alaska Miners Association Annual Meeting, Anchorage, AK, November 3-7, 2014.
Kokaly, R.F., Hoefen, T.M., Graham, G.E., Kelley, K.D., Johnson, M.R., Hubbard, B.E., and Goldfarb, R.J., 2015, Mapping surficial minerals at high latitudes: the USGS 2014 imaging spectrometer data collection in Alaska: International Geoscience and Remote Sensing Symposium (IGARSS 2015), Milan, Italy, July 26-31, 2015.
Kokaly, R.F., Hoefen, T.M., Graham, G.E., Kelley, K.D., Johnson, M.R., Hubbard, B.E., Goldfarb, R.J., Buchhorn, M., and Prakash, A., 2016, Mineral information at micron to kilometer scales: laboratory, field, and remote sensing imaging spectrometer data from the Orange Hill porphyry copper deposit, Alaska, USA: International Geoscience and Remote Sensing Symposium (IGARSS 2016), Beijing, China, July 10-15, 2016.
Prakash, A., Buchhorn, M., Cristobal, J., Kokaly, R.F., Graham, P.R., Waigl, C.F., Hampton, D.L., Werdon, M., Guldager, N., Bertram, M., and Stuefer, M., 2015, Field-Based and Airborne Hyperspectral Imaging for Applied Research in the State of Alaska: American Geophysical Union Fall Meeting, San Francisco, California, December, 2015. View Prakash AGU 2016 abstract.