Geologic Model of the Geothermal Anomaly at Pilgrim Hot Springs, Seward Peninsula, Alaska

Abstract

Pilgrim Hot Springs has a known shallow geothermal reservoir with temperatures approaching 91˚C in the top 100 meters of the system that underlies the main hot springs area of 1.5 km2. The deeper reservoir is less understood with similar temperatures at the basement surface 320 meters directly beneath the hot springs. The aspect of this research is to create a stratigraphic model and delineate potential flow paths for the upflow zone of the geothermal anomaly. Lithology, well logs, temperature data, and magnetotelluric survey maps indicate a shallow outflow aquifer at 50 meters depth, a low permeability clay cap at 200-275 meters depth above the deeper reservoir, and an upflow of 90°C geothermal fluids that correlates to an indurated zone to the basement surface. The geothermal fluids may be flowing from a fault in the bedrock in the center of the hot springs although the deeper source is speculative.