A COMPARISON OF CLAY AND TRAVERTINE MATERIAL FROM THE BORAX LAKE AND MICKEY HOT SPRINGS GEOTHERMAL SYSTEMS, ALVORD BASIN, OREGON

We investigated the mineralogy of travertine and clays associated with the Borax Lake and Mickey Hot Springs geothermal systems in the Alvord Basin of southeast Oregon. Together, the two areas comprise approximately 235 mapped spring vents, and are located on the edge of the Great Basin, where geothermal systems arising from extensional tectonics and high crustal heat flow are common. Geothermal fluids from the two areas are similar; both areas demonstrate sodium-bicarbonate-chloride-type waters with high sulfate content, and standard geothermometers indicate reservoir temperatures in the range of 200 – 250 oC for both areas. The Borax Lake area consists of about 178 springs, aligned along the trace of a northeast-striking normal fault. Spring temperatures at Borax Lake range from 23.9 to 95.5 oC (average 62.1 oC), and pH ranges from 5.8 to 8.6 (average 7.3). Mickey Hot Springs, located 45 km to the northeast of Borax Lake, includes about 57 spring vents organized in discrete pods, ranging in temperature from 33.7 to 97.7 oC (average 79.1) and pH ranging from 5.6 to 9.3 (average 7.7).

In spite of superficial similarities, there are distinct differences between the two systems; for example, there is fumerolic discharge at Mickey Hot Springs, which is absent at Borax Lake. In order to further investigate the differences between the two areas we collected a series of geothermal muds, sinter, travertine, and loose rock material from both systems. Preliminary analyses of these samples show definite differences between the areas. All travertine material collected was predominately calcium carbonate, with minor smectite. At Mickey Hot Springs the thermal mud samples were predominately smectite; however, the samples also contained minor amounts of kaolinite and haloysite. One surface rock sample also contained illite, and the older sinter material contained amorphous silica rather than carbonate material. The Borax Lake samples indicate much lower temperature near the surface, as smectite was the only clay detected, and all other surface deposits were calcium carbonate. The results of our preliminary analyses suggest that boiling is occurring closer to the surface in the Mickey Hot Springs system, and that chemically the Mickey system has been more diverse in the past.