TB Occurrence, Kupreanof Island, Petersburg Borough, Alaska, USAi
| Regional Level Types | |
|---|---|
| TB Occurrence | Occurrence |
| Kupreanof Island | Island |
| Petersburg Borough | Borough |
| Alaska | State |
| USA | Country |
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Latitude & Longitude (WGS84):
56° 31' 48'' North , 133° 31' 14'' West
Latitude & Longitude (decimal):
Type:
Köppen climate type:
Nearest Settlements:
| Place | Population | Distance |
|---|---|---|
| Kake | 570 (2017) | 55.9km |
Location: This occurrence is near the center of a large, vivid yellow-orange altered zone on southern Kupreanof Island that extends for up to a mile or more in all directions from the coordinates given above and can be seen for miles from the air. The site is plotted about 2 miles north of the center of Kushneahin Lake at the southeast corner of section 34, T. 61 S., R. 76 E.
Geology: Extensive vivid exposures of yellow-orange altered rhyolite, rhyolite tuff, and rhyolitic glass of Quaternary or Tertiary age crop out in many of the creeks and cut banks in the vicinity (Brew and others, 1984; Brew, 1997). Several exposures were briefly examined by the USGS in 1982 and 1996. Disseminated pyrite is present locally but there are no obvious signs of copper, molybdenum, or other ore minerals. The rocks are pervasively altered and locally brecciated. Several grab samples of the more-altered rhyolite and associated rocks show 5 parts per million (ppm) or less copper and molybdenum. The pyrite and host rocks are part of a large felsic igneous system; possibly a rhyolite dome. The surrounding area is heavily wooded but aerial reconnaissance shows widespread exposures of similar orange and yellow, iron-stained rocks over an area at least several miles in diameter. Although no obvious mineralization has been found, the site is included because this altered zone is so large, so prominent, and it indicates the presence of a very large felsic hydrothermal system. Resource Associates of Alaska (RAA) staked a hundred claims here in 1973, referring to it as the TB block. Several exposures were briefly examined by Still and others (2002) in the late 1990's. A grab sample contained only 425 ppm zinc.
Workings: None other than probable examination by various industry and government geologists who have worked in the area.
Age: Quaternary or Tertiary.
Alteration: Pyritization, silicification, and kaolinization(?).
Commodities (Major) - Cu ?, Mo ? Zn
Development Status: None
Deposit Model: Highly altered felsic igneous system.
Select Mineral List Type
Standard Detailed Gallery Strunz Chemical ElementsGallery:
List of minerals arranged by Strunz 10th Edition classification
| Group 2 - Sulphides and Sulfosalts | |||
|---|---|---|---|
| ⓘ | Pyrite | 2.EB.05a | FeS2 |
Other Databases
| Link to USGS - Alaska: | PE019 |
|---|
Other Regions, Features and Areas containing this locality
North America PlateTectonic Plate
- Alexander DomainDomain
- Alexander TerraneVolcanic Arc
USA
- Alaska
- Petersburg Borough
- Kupreanof Mining DistrictMining District
- ⭔Wrangell-Petersburg Census AreaBorough
- Petersburg Borough
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References
Grybeck, Donald J.; Berg, Henry C.; Karl, Susan M. (1984) Map and description of the mineral deposits in the Petersburg and eastern Port Alexander quadrangles, southeastern Alaska. Open-File Report 84-837. US Geological Survey 87 pp. doi:10.3133/ofr84837
Brew, David A., Ovenshine, A.T., Karl, Susan M., Hunt, S.J. (1984) Preliminary reconnaissance geologic map of the Petersburg and parts of the Port Alexander and Sumdum 1:250,000 quadrangles, southeastern Alaska. Open-File Report Vol. 1984 (84-405) US Geological Survey doi:10.3133/ofr84405
