Geologic descriptionExtensive 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. |
