2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 13
Presentation Time: 11:15 AM


WANG, Bronwen, U.S. Geol Survey, 4200 University Dr, Anchorage, AK 99508, WANTY, Richard, U.S. Geological Survey, P.O. Box 25046, MS 973, Denver, CO 80225-0046 and VOHDEN, Jim, Alaska Department of Nat Rscs, Fairbanks, AK 99775, bwang@usgs.gov

The U.S. Geological Survey (USGS) and Alaska Department of Natural Resources (ADNR) are continuing investigations on element mobility in mineralized and non-mineralized areas of the Yukon-Tanana Upland in east-central Alaska. The chemistry of stream water is evaluated in the context of regional bedrock geology and geologic structure. Sampling sites were located in the Big Delta B2 quadrangle, which includes the mineralized areas of the Pogo claim block. The area is typified by steep, subarctic-alpine, boreal forest catchment basins. Bedrock is composed of metamorphic rocks and younger plutons. Samples were collected from catchments that either cross structural features and lithologic contacts, or are underlain by a single lithology. Waters are generally dilute (< 213 mg/L TDS), and are classified as Ca2+ and Mg2+ - HCO3- to Ca2+ and Mg2+ - SO42- waters. The metamorphic lithologies are more SO42- dominated than the intrusive units. The major-ion chemistry of the waters reflects a rock-dominated aqueous system. Trace-element concentrations in water are generally low. However, As and Sb are detectable near mineralized areas but in most cases rapidly attenuate downstream and processes other than simple dilution control the concentrations of these trace elements. The SO42- concentrations increase downstream near the mineralized areas but the concentration may not be directly related to mineralization. More work is necessary to determine what proportion of the increase in SO42- concentration is attributable to the sulfide mineral oxidation, as opposed to water influenced by the underlying metamorphic units.