COLUMBIUM - AND RARE-EARTH ELEMENT-BEARING DEPOSITS AT BOKAN MOUNTAIN, SOUTHEAST ALASKA By J. Dean Warner and James C. Barker Alaska Field Operations Center * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * OFR - 33-89 UNITED STATES DEPARTMENT OF THE INTERIOR Manuel Lujan, Jr., Secretary BUREAU OF MINES T.S. Ary, Director TABLE OF CONTENTS Page Abstract ........................................................ 1 Introduction ....................... 2 Acknowledgments ................................................. 4 Location, access, and physiography .............................. 5 History and production ............. 5 Geologic setting .................................. 9 Trace element analyses of the peralkaline granite .............. 11 Nature of Bureau investigations ................................. 13 Sampling methods and analytical techniques .................... 13 Analytical interference, limitations, and self-shielding ...... 13 Resource estimation methods ................................... 15 Prospect evaluations .......................................... 16 Shear zones and fracture-controlled deposits .................... 18 Ross Adams mine ................. 18 Sunday Lake prospect.......................................... 21 I and L No. 1 and Wennie prospects ............................ 27 Other Occurrences ............................................. 31 Altered peralkaline granite ................................. 31 Dotson shear zone ........................................... 35 Resources ................................................... 35 Pegmatite deposits .............................................. 35 Northwestern Bokan Mountain area .............................. 36 ILM prospect .................................................. 36 Little Jim Prospect .................................. 45 Little Joe prospect .................................. 45 Irene-D prospect .............................................. 48 Dike deposits ................................................... 54 Geiger prospect ............................................... 56 I and L prospect .............................................. 64 Dotson prospect ................................................ 77 Cheri prospect ................................................ 90 Upper Cheri Prospect .......................................... 95 Shore prospect ................................................ 97 Geoduck Prospect .............................................. 104 Placer prospects - Kendrick Bay and Moira Sound ................. 106 Discussion ...................................................... 109 Summary of resource estimates ................................... 112 Conclusions ..................................................... 116 References ...................................................... 117 Appendix A.--Field sample numbers versus map numbers ............ 119 Appendix B.--Additional analyses of samples reported in text .... 124 Appendix C.--Head assays of bulk samples from Bokan Mountain area deposits; for comparison to sample results subject to self-shielding and elemental interference ...................... 197 ILLUSTRATIONS 1. Location of Bokan Mountain in southeast Alaska ................ 6 2. Bokan Mountain area and locations of prospects ................ 7 3. Geology of the Bokan Mountain granite ......................... 10 i ILLUSTRATIONS--Continuted Page 4. Plan map and cross sections of the Ross Adams mine and ore body ..................................................... 20 5. Locations of samples collected from the west wall of the Ross Adams pit .................................................... 22 6. Geologic and sample location map of the Sunday Lake prospect.. 28 7. Geologic and sample location map of hte I and L No.'s 1 and 2 and Wennie prospect areas .................................... 30 8. Other occurrences of shear zone and fracture-controlled mineralization.. 33 9. Geologic and sample location map of the northwestern Bokan Mountain area ................................................ 37 10. Geologic and sample location map of the ILM prospect .......... 40 11. Geologic and sample location map of the Little Joe prospect... 47 12. Geologic, magnetic survey, and sample location map of the Irene-D prospect ............................................. 49 13. Photograph showing traces of the Dotson, Cheri, and Geoduck dike systems ................................................. 55 14. Geiger prospect dike system ................................... 57 15. Map of the Geiger prospect between Perkins Creek and south arm Moira Sound ........................................ 58 16. Map of the Geiger prospect north of south arm Moira Sound ........................................................ 59 17. Geologic and sample location map of the I and L prospect ...... 65 18. Geologic cross section A-A', I and L prospect ................. 66 19. Geologic cross section B-B', I and L prospect ................. 67 20. Geologic cross section C-C', I and L prospect ................. 68 21. Geologic cross section D-D', I and L prospect ................. 69 22. Geologic cross section E-E', I and L prospect ................. 70 23. Radioactive dikes at Bokan Mountain generally contain fine to medium grain Cb-REE-Zr minerals suspended in a matrix of quartz and Na-feldspar ....................................... 72 24. Geologic and sample location map of the Dotson prospect ....... 78 25. Photograph of the Dotson Dike ................................. 80 26. Photomicrograph and backscatter SEM image of samples from the Dotson prospect .............................................. 81 27. Geologic and sample location map of the Cheri prospect ........ 91 28. Geologic and sample location map of the upper Cheri prospect.. 96 29. Geolduck and Shore prospect area .............................. 99 30. Profile of Kendrick Bay ....................................... 107 31. Percent composition of REO at Bokan Mountain as compared to U.S. and principal world REO deposits ........................ 110 TABLES 1. Commodities present and typical range of values in samples from deposits at Bokan Mountain .. 3 2. Production from the Ross Adams mine ........................... 8 ii TABLES--Continued Page 3. Mean (X) and range (R) of values in samples of Bokan Mountain granite ...................................................... 12 4. Analytical methods and detection limits ....................... 14 5. Average measured tonnage factors .............................. 17 6. Deposit types and prospects investigated ...................... 19 7. Analyses of samples collected at the Ross-Adams mine .......... 23 8. Partial log of Standard Metals diamond drill hole KS-46, Ross-Adams mine .............................................. 26 9. Partial log of Standard Metals diamond drill hole KU-17, Ross-Adams mine .............................................. 26 10. Partial log of Standard Metals diamond drill hole KS-60, Ross-Adams mine .............................................. 26 11. Analyses of samples collected at the Sunday Lake prospect ..... 29 12. Analyses of samples collected at the I and L No. 1 and Wennie prospects.. 32 13. Analyses of samples collected from other occurrences of shear zone or fracture-controlled mineralization ................... 34 14. Analyses of samples collected from northwest Bokan Mountain... 38 15. Analyses of samples collected at the ILM prospect ............. 42 16. Analyses of samples collected at the Little Jim prospect ...... 46 17. Analyses of samples collected at the Little Joe prospect ...... 50 18. Analyses of samples collected at the Irene-D prospect ......... 52 19. Analyses of samples collected at the Geiger prospect .......... 60 20. SEM identification of REE-columbium-radioactive minerals in the I and L and Dotson dike prospects ........................ 73 21. Analyses of samples collected at the I and L prospect ......... 74 22. Analyses of samples collected from the Dotson dike system ..... 82 23. Dotson prospect indicated resources ........................... 89 24. Analyses of samples collected at the Cheri prospect ........... 93 25. Analyses of samples collected at the Upper Cheri and Upper Cheri Extension prospects .................................... 98 26. Analyses of samples collected at the Geoduck and Shore prospects........................ .................. 100 27. Placer sample results from the Bokan Mountain area ............ 108 28. Summary of grade and indicated tonnage for Bokan Mountain deposits ............................................ 113 29. Summary of grade and inferred tonnage for Bokan Mountain deposits ............................................ 114 30. Summary of principle resources in the Bokan Mountain deposits. 115 UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT cps counts per second of gamma ray radiation ft foot ft3 cubic foot g gram in inch lb pound mi mile mm millimeter MM million pct percent ppb parts per billion ppm parts per million st short ton t oz troy ounce yd3 cubic yard iv COLUMBIUM- AND RARE-EARTH ELEMENT-BEARING DEPOSITS AT BOKAN MOUNTAIN, SOUTHEAST ALASKA By J. Dean Warner!' and James C. BarkerY/ ABSTRACT From 1984 through 1987, the Bureau of Mines investigated numerous prospects and new discoveries of columbium, rare-earth elements (REE), uranium, zirconium, and other metals associated with the multi-phased peralkaline granite at Bokan Mountain, southeastern Alaska. This report summarizes the mineral evaluations