MacKevett reported in 1963 on the Bokan Mountain uranium-thorium area, which includes an area of about 71 square miles on the southern part of Prince of Wales Island and which is largely underlain by plutonic rocks. Metasedimentary and metavolcanic rocks, probably of Devonian age, underlie about 5 percent of the area. The plutonic rocks, which are probably Cretaceous in age, range from pyroxenite to peralkaline granite and syenite, but they consist chiefly of diorite, quartz diorite, granodiorite, and quartz monzonite. The peralkaline granite, an uncommon rock type, forms a boss about 3 square miles in areal extent, which contains abnormal quantities of many minor elements. Pegmatite and aplite dikes are common in and near the boss, but uncommon elsewhere. Fine-grained mafic dikes, chiefly of andesite and dacite, are abundant throughout most of the area, and diabase, rhyolite(?), and quartz latite(?) dikes are sparsely distributed. The rocks are cut by numerous faults and joints.
Most of the uranium-thorium deposits are genetically related to the peralkaline granite, and they occur either in the boss or within an altered (albitized) aureole, as much as 1 to 2 miles wide, that surrounds the boss. The uranium-thorium deposits have four modes of occurrence:
1) concentrations of uranium-thorium-bearing accessory minerals in the peralkaline granite, a process which accounts for a small part of the Ross-Adams deposit;
2) veins or local replacements that contain uranium-thorium minerals of hydrothermal origin in or near fractures are the dominant occurrences of most of the Bokan Mountain area uranium-thorium deposits know as of 1963.
3) disseminated primary uranium-thorium minerals that are syngenetic in pegmatite and aplite dikes; and
4) uranium-thorium minerals of hydrothermal origin occupying interstices in clastic metasedimentary rocks, the only known occurrence of this type in the area is at the Cheri prospect.
Many radioactive minerals and a few minerals that contain rare earths and niobates were identified during the investigation. The only uranium production from the area, which, as of March 1959, constituted the only uranium production from Alaska consisting of about 15,000 tons of high-grade ore that was mined from the Ross-Adams deposit during the summer and fall of 1957. The Bokan Mountain area also contains copper and gold propects, which are the sites of a few old mines, and iron deposits that have recently interested mining companies (circa 1963).
The minor elements of the rocks and ores were investigated by semiquantitative spectrographic analyses, and an endeavor was made to trace the distribution of 29 minor elements throughout the plutonic rock sequence, [see pages 82, 92, and 108-109. Note the DLs were very high.]
For associated Plates:
Plate 1 - https://pubs.usgs.gov/bul/1154/plate-1.pdf
Plate 2 - https://pubs.usgs.gov/bul/1154/plate-2.pdf
Plate 3 - https://pubs.usgs.gov/bul/1154/plate-3.pdf
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