Assessing Hydrothermal System Dynamics and Character by Coupling Hyperspectral Imaging with Historical Drilling Data: Long Valley Caldera, CA, USA

Abstract

Synoptic maps of hydrothermal alteration have previously been constructed for Long Valley Caldera located in central-eastern California, however the purpose of this work is to determine what continuous surface alteration information can or cannot reveal about alteration at depth and thus hydrothermal system dynamics and character. Mineral maps produced from hyperspectral imaging are compared with known geology including historical drilling data. A good correlation is obtained between the types of alteration found at the surface and that found at depth. Generally, the temperatures and alteration measured at depth echo the alteration (and implied temperatures) that is subsequently mapped at the surface. However some specific comparisons at individual well sites still remain inconclusive due to external variables that are difficult to control and measure such as intense vegetation coverage, secondary weathering and transport, and instrument limitations. An attempt to rise above some of these issues is made by exploring trends of alteration and thus hydrothermal system character by using alteration density plots. Such plots confirm current working models of hydrothermal system dynamics and geometry and support new geothermal prospecting in the region.