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Geochemical analyses of rock samples collected from mineral deposits and intrusions of the Bokan Mountain peralkaline granitic complex, Prince of Wales Island, southeastern Alaska

October 27, 2017

This data set compiles the major and trace element chemistry of rock samples collected by the U.S. Geological Survey (USGS) 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. The Ross-Adams mine on Bokan Mountain exploited a uranium-thorium deposit intermittently from the late 1950s to 1971, and remains the only uranium producer in Alaska. 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) that are enriched in rare earth elements (REE). Ucore Rare Metals has reported an inferred resource for the combined zones as 5.275 million metric tons of ore at 0.654 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 (http://ucore.com/Ucore_43-101.pdf). This data release provides the analytical results of 153 rock hand samples collected by USGS geologists during site visits to Bokan Mountain in 2010, 2011, and field studies during 2014. The samples represent a variety of rock types associated with the Bokan Mountain igneous complex, including mineral deposits, prospects and occurrences, along with examples of unaltered intrusions of the pluton. The samples were analyzed for 55 major and trace elements using inductively coupled plasma-atomic emission spectrometry (ICP-AES) and inductively coupled plasma-mass spectrometry (ICP-MS) and 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 Bokan Mountain and its mineral deposits.