Electrical Resistivity Anomalies at Newberry Volcano, Oregon: Comparison with Alteration Mineralogy in Geo Corehole N-1

Abstract

Corehole N-1, drilled on the south flank of Newberry volcano in Oregon by GEO Operator Corp under a cooperative agreement with DOE, encountered about 15 separates horizons between 2800 ft and 4000 ft that are good electrical conductors as shown by an induction log. These conductors correlate with horizons of altered basaltic, andesitic and lactitic ash and tuff in a lithologic section composed predominantly of basaltic andesite flows. X-ray diffraction and scanning electron microscope analyses show the dominate alteration type to be a calcium smectite and we believe that the alteration is low temperature in origin. Surface electrical geophysical survey have detected a widespread resistivity low in the Newberry area. A portion of this resistivity low is believe to be associated with the high temperature hydrothermal system in Newberry caldera, whereas other portions of low appear to be caused by the altered horizon on the flanks of the volcano. Delineation of the high temperature system by electrical surveys may be difficult or impossibly because of effects form the altered rocks.