2003 Seattle Annual Meeting (November 25, 2003)
Paper No. 164-8
Presentation Time: 3:15 PM-3:30 PM

AQUEOUS GEOCHEMISTRY OF THERMAL WATERS IN THE ALVORD BASIN, OREGON

KOSKI, Angie, Environmental Science, Univ of Idaho, Moscow, ID 83844, akoski@tds.net and WOOD, Scott, Geological Sciences, Univ of Idaho, P.O. Box 443022, Moscow, ID 83844-3022

The Alvord Basin is located in Harney County, Oregon and is included in the Oregon Plateau of the northern Basin and Range province of the southwestern United States. The basin is a broad, flat, graben valley bounded by several mountain ranges. Faults in the area indicate strike-slip faulting and offset resulting from East-West extension of the plateau. Rock formations in the area are of volcanic origin and sediments on the valley floor include sand, gravel, silt, and lacustrine sediments. Three main groups of hot springs are located in the valley: Borax Lake Hot Springs, Alvord Hot Springs, and Mickey Hot Springs. The geochemistry of these springs has been explored to determine processes contributing to their chemical composition. Several springs from each location were sampled on 5 separate occasions over the course of a year. Thermal waters in the area are characterized as mixed bicarbonate-chloride waters with significant levels of sulfate. These waters also have high levels of As (1-5 mg/L) and B (8-29 mg/L). There is little variation from spring to spring within each group; however, differences are evident between spring groups. The chemical compositions of the springs have not varied considerably throughout the year. Waters from Alvord Springs are the most concentrated with the highest levels of total dissolved solids, Cl-, K+, Mg2+, and Na+. Waters from Borax Springs have the highest concentrations of SO42- and Ca2+. Waters from Mickey Springs have lowest levels of Mg2+. Surface temperatures of the hot springs range from 30C to over 90C, while estimates of reservoir temperatures by chemical geothermometry vary from 120C to over 220C. In general, calculated reservoir temperatures are highest for Mickey Springs and lowest for Borax Springs. Thermal springs in the Alvord Basin originate from meteoric water that circulates through the crust gaining heat and chemical constituents. There is minimal mixing of deep thermal waters with shallow groundwaters. Companion isotopic studies and geochemical modeling should shed additional light on the origin of these waters.

2003 Seattle Annual Meeting (November 25, 2003)
Session No. 164--Booth# 61
Geochemistry, Other II: A Geochemical Potpourri
Washington State Convention and Trade Center: 204
1:30 PM-5:30 PM, Tuesday, November 4, 2003

Geological Society of America Abstracts with Programs, Vol. 35, No. 6, September 2003, p. 407

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