Relative Ages of the Borax Lake and Mickey Geothermal Systems, Alvord Basin, Oregon Usa: Preliminary Evidence from Silica Phase Transitions

Abstract

We investigated the mineralogy of sinter and travertine deposits associated with the Borax Lake and Mickey geothermal systems in the Alvord Basin, southeast Oregon. Together, the two areas comprise approximately 235 spring vents, located on the edge of the Great Basin, where geothermal systems arising from extensional tectonics and high crustal heat flow are common.

Both the Mickey and Borax Lake systems demonstrate sodium-bicarbonate-chloride-type waters. Surface temperature in both systems range between 24 and 98oC and standard geothermometers indicate reservoir temperatures of 200 – 250oC. Despite the similarity in fluid chemistries, mineral precipitates vary significantly between the two systems. The Borax Lake system is dominated by calcite with minor amounts of amorphous silica (opal-A) and rare microcrystalline quartz. The Mickey system is more diverse and includes: quartz, opal-A, opal-CT, microcrystalline quartz, hematite, and minor calcite. Using silica phase transformations as an indicator of relative age, we suggest that the occurrence of opal-A, opal-CT and quartz at Mickey indicates the system is older than the Borax Lake system.