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Geochemical analyses of rock samples collected from the Dotson and I and L rare earth element deposits of the Bokan Mountain peralkaline igneous complex, Prince of Wales Island, southeastern Alaska

July 23, 2021

This data release presents the major and trace element chemistry of rock samples collected by the U.S. Geological Survey (USGS) from trenches, channel cuts, test pits, and surface exposures of the Dotson and I and L Zone rare earth element deposits at Bokan Mountain, located in the southern part of Prince of Wales Island, southeastern Alaska. Bokan Mountain was formed by an Early Jurassic peralkaline igneous complex that intruded into lower Paleozoic rocks of the Alexander terrane of southeast Alaska. The pluton and surrounding country rocks host numerous mineral deposits and occurrences, including heavy rare earth element (HREE)-rich pegmatites and felsic dikes, as well as mineral deposits rich in uranium, thorium, HREE, and fluorine. Recent exploration by Ucore Rare Metals Inc. (http://ucore.com/) at Bokan Mountain has focused on the Dotson and I and L Zones, which together form a 2.5-km-long, 50 m-wide zone of thin felsic dikes and pegmatites (each rarely more than 2-m-wide individually) that are enriched in rare earth elements (REE). Ucore Rare Metals has reported an indicated resource of 4.788 million metric tons of ore at 0.602 percent total REE oxides and an inferred resource of 1.050 million metric tons of ore at 0.603 percent total REE oxides, using a cutoff of 0.4 percent total REE oxides; about 40 percent of the total REE oxides in these dikes and pegmatites are the HREE (Ucore Rare Metals, 2020). There is also potential for the production of by-product Nb, Zr, and Ti. This data release provides the analytical results of 42 rock samples collected by the author during a site visit to Bokan Mountain in August 2014. The samples represent a complete transect along the entire length of the combined I and L and Dotson Zones from the margin of the pluton to tidewater in Kendrick Bay. They provide a measure of the REE abundances and their variation throughout the deposit as well as material for detailed isotopic and mineral chemistry studies (Taylor and others, 2016, 2017). The samples were analyzed for 57 major and trace elements using inductively coupled plasma-atomic emission spectrometry (ICP-AES), inductively coupled plasma-mass spectrometry (ICP-MS and ICP-MSREE), and inductively coupled plasma-optical emission spectrometry for zirconium (ICPOES). The samples were also analyzed for major elements using wavelength dispersive x-ray fluorescence spectrometry (WDXRF). This data set is provided for future use in geologic, exploration, and environmental background studies of the Dotson and I and L Zone deposits. References listed here provide geologic context and additional descriptions on the geologic features represented by the rock samples: Barker, J.C., and Van Gosen, B.S., 2012, Alaska's rare earth deposits and resource potential: Mining Engineering, v. 64, no. 1, p. 20-32. Dostal, J., Karl, S.M., Keppie, J.D., Kontak, D.J., Shellnutt, J.G., 2013, Bokan Mountain peralkaline granitic complex, Alexander terrane (southeastern Alaska)-Evidence for Early Jurassic rifting prior to accretion with North America: Canadian Journal of Earth Sciences, v. 50, 678-691. Dostal, Jaroslav, Kontak, D.J., and Karl, S.M., 2014, The Early Jurassic Bokan Mountain peralkaline granitic complex (southeastern Alaska)-Geochemistry, petrogenesis and rare-metal mineralization: Lithos, v. 202-203, p. 395-412. Dostal, Jaroslav, and Shellnutt, J.G., 2016, Origin of peralkaline granites of the Jurassic Bokan Mountain complex (southeastern Alaska) hosting rare metal mineralization: International Geology Review, v. 58, no. 1, p. 1-13. Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, David, 2010, The principal rare earth elements deposits of the United States-A summary of domestic deposits and a global perspective: U.S. Geological Survey Scientific Investigations Report 2010-5220, p. 28-34. Available at http://pubs.usgs.gov/sir/2010/5220/. MacKevett, E.M., Jr., 1963, Geology and ore deposits of the Bokan Mountain uranium-thorium area, southeastern Alaska: U.S. Geological Survey Bulletin 1154, 125 p., 5 plates. McCafferty, A.E., Stoeser, D.B., and Van Gosen, B.S., 2014, Geophysical interpretation of U, Th, and rare earth element mineralization of the Bokan Mountain peralkaline granite complex, Prince of Wales Island, southeast Alaska: Interpretation, v. 2, no. 4, p. SJ47-SJ63. Philpotts, J.A., Taylor, C.D., Tatsumoto, Mitsunobu, and Belkin, H.E., 1998, Petrogenesis of late-state granites and Y-REE-Zr-Nb-enriched vein dikes of the Bokan Mountain stock, Prince of Wales Island, southeastern Alaska: U.S. Geological Survey Open-File Report 98-459, 71 p. Staatz, M.H., 1978, I and L uranium and thorium vein system, Bokan Mountain, southeastern Alaska: Economic Geology, v. 73, no. 4, p. 512-523. Stoeser, D.B., 2013, Mineralogy and mineral paragenesis of the Dotson Ridge HREE deposit, Bokan Mountain, Prince of Wales Island, Alaska: Geological Society of America Abstracts with Programs, v. 45, no. 7, p. 276. Taylor, C.D., Aleinikoff, J.N., Holm-Denoma, C.S., Neymark, L.A., Bala, S.A., Pascarelli, S.E., Pillers, R.M., Karl, S.M., Van Gosen, B.S., Morgan, L.E., and Cosca, M.A., 2016, New geochronologic constraints on the formation and hydrothermal enrichment of the Bokan Mountain peralkaline igneous complex and associated HREE deposits, southeastern Alaska, USA: Geological Society of America Abstracts with Programs, v. 48, no. 7, Abstract no. 286288. Taylor, C.D., Lowers, H.A., Adams, D.T., and Robinson, R.J., 2017, Geochemistry and mineralogy of the Dotson Zone HREE deposit in the Bokan Mountain peralkaline igneous complex, southeastern Alaska, USA: Proceedings of the 14th SGA Biennial Meeting, 20-23 August 2017, Quebec City, Canada, p. 1329-1332. Thompson, T.B., 1988, Geology and uranium-thorium mineral deposits of the Bokan Mountain granite complex, southeastern Alaska: Ore Geology Reviews, v. 3, p. 193-210. Ucore Rare Metals, Inc., 2020, Ucore Increases Bokan Mineral Resource with Critical Co-Products: Ucore Rare Metals press release, October 15, 2019. Accessed September 29, 2020, at https://www.newsfilecorp.com/release/48774/Ucore-Increases-Bokan-Minera…. Van Gosen, B.S., and Taylor, C.D., 2017, Geochemical analyses of rock samples collected from mineral deposits and intrusions of the Bokan Mountain peralkaline granitic complex, Prince of Wales Island, southeastern Alaska: U.S. Geological Survey data release, https://doi.org/10.5066/F7KD1WVC. Warner, J.D., and Barker, J.C., 1989, Columbium- and rare-earth element-bearing deposits at Bokan Mountain, southeast Alaska: U.S. Bureau of Mines Open File Report 33-89, 196 p.