MINERALOGICAL STUDIES OF THE HYDROTHERMAL SYSTEM IN NEWBERRY VOLCANO DRILL HOLE 2, OREGON.

Studies of secondary mineral distribution, whole-rock chemical compositions, isotopes, and fluid inclusions are being conducted on the core from Newberry Volcano drill hole 2. Rocks from the drill core are divided into 3 major intervals on the basis of their alteration pattern, which is controlled by rock permeabilities, primary lithologies, and temperatures. Incomplete alteration of pumice-rich lithic tuff layers in the upper part of the altered section and lack of self-sealing in fractures of most lava flows suggest that the hydrothermal system is young. Most of the secondary minerals could have been formed at temperatures near those present today; maximum measured temperature was 265 degree C at the bottom of the hole. Fluid inclusions indicate that past temperatures in the deeper part of the drill hole may have been as much as 100 degree C hotter than presently measured temperatures.