| Abstract |
Mt. Spurr is an ice and snow-covered andesitic volcano located at the northern extent of the Aleutian arc in south central Alaska. Previous workers have identified a prospective geothermal system on the south side of the volcano. This research applies aqueous and mineralogical geochemical investigations at Mt. Spurr in order to characterize the hydothermal system, focusing on the possible extent, temperature, origin of fluids, and fluid pathways occurring in the system. Three spatially distinct endmember compositions have been identified: 1) moderate temperature (~50?C), acidic, bicarbonate-poor, d18O and dD-enriched waters from Crater Lake, 2) low temperature (14-40?C), neutral, bicarbonate and Mg-rich, slightly d18O and dD-enriched peripheral waters, and 3) cold (<9?C), neutral, sulfate-rich, dilute/meteoric waters. Spring and seep waters sampled in this study represent shallowly circulating meteorically-derived waters that have variously interacted with rock, incorporated dissolved steam, possibly mixed with andesitic water, and been heavily diluted by cold meteoric water. Fluid pathways are likely controlled by local east-northeast and north-northeast and northwest trending faults that behave similarly to oblique-slip regional structures that bound the Cook Inlet. Permeability in andesitic flows that cover the field area is likely quite high, but clay minerals in weathered volcanic ash in between flows and in underlying Cook Inlet sediments likely act as barriers to deep circulation of meteoric water and upwelling of deeply sourced hydrothermal fluids. Precise mapping of fault structures that act as conduits to fluid flow and deeper drilling will enhance the understanding of the hydrothermal system at Mt. Spurr. |