Secondary Mineralogy of Core from Geothermal Drill Hole CTGH-1, High Cascade Range, Oregon

Abstract

Geothermal drill hole CTGH-1, located near Breitensbush Hot Springs in the Cascade Mountain of northwest Oregon, was drilled to a depth of 1463 m. The maximum reported temperate oat 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 space between breccia fragments are partly to completely filled by secondary minerals: hematite, goethite, smectite, celadonite, zeolite minerals (analcime, chabazite, clinoptilolite, erionite, heulandite, mordenite, phillipsite, scolecite, thomonite, and wellsite), silica minerals (chalcedony, cristobalite, cristobalite and quartz), native copper, calcite, apatite, and adularia. All of the above minerals are compatible with the present low temperature conditions.