Geothermal drill hole CTGH-1, located near Breitenbush Hot Springs in the Cascade Mountains of northwest Oregon, was drilled to a depth of 1463 m. The maximum reported temperature at the bottom of the drill hole was 96.4??C. The drill core consists predominantly of basalt to basaltic andesite lava flows, tuffs, and volcanic breccia. Red to orange iron-oxide stained tuffs are at least partly altered to smectite. Vesicles, fractures, and open spaces between breccia fragments are partly to completely filled by secondary minerals. All of the minerals are compatible with the present low-temperature conditions.
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Secondary mineralogy of core from geothermal drill hole CTGH-1, High Cascade Range, Oregon