TB

Occurrence, Inactive

Commodities and mineralogy

Main commodities Cu; Mo; Zn
Ore minerals pyrite

Geographic location

Quadrangle map, 1:250,000-scale PE
Quadrangle map, 1:63,360-scale C-5
Latitude 56.5301
Longitude -133.5211
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

Geologic description

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 1990s. A grab sample contained only 425 ppm zinc.
Geologic map unit (-133.52285533975, 56.5297447611755)
Mineral deposit model Highly altered felsic igneous system.
Age of mineralization Quaternary or Tertiary.
Alteration of deposit Pyritization, silicification, and kaolinization(?).

Production and reserves

Workings or exploration None other than probable examination by various industry and government geologists who have worked in the area.
Indication of production None

References