GEOCHEMICAL MODELING OF AQUEOUS- AND MINERAL-PHASE IRON-HYDROXIDE CHEMISTRY IN ARCTIC STREAMS NEAR THE RED DOG MINE, NORTHWEST ALASKA

Weathering of surface-exposed rocks containing high concentrations of metals may adversely affect water, soil, and sediment quality. In order to properly remediate mine sites, it is necessary to determine pre-mining background metal concentrations. Therefore, developing a methodology to reliably estimate pre-mining background in mined areas is essential. Formation of Fe-hydroxide precipitates in surface water bodies weathering mineralized rocks can greatly affect surface water quality. This project will study the surface water chemistry of the Red Dog, Ikalukrok and Cub Creeks in northwest Alaska, located 90 km above the arctic circle. Prior to mining, Red Dog Creek eroded three surface deposits comprising the Red Dog Mine, a massive Zn-Pb-Fe sulfide body. Massive amounts of Fe-hydroxides precipitated along Red Dog Creek. Cub and Ikalukrok Creeks erode surface showings of similar mineralization. Precipitates similar to those found at Red Dog currently form in both Cub and Ikalukrok Creeks. We believe that the geochemical dynamics associated with formation of the precipitates are the primary control on aqueous geochemistry in these arctic streams. This poster will present mineralogical and chemical analyses of precipitate samples collected at Cub and Ikalukrok Creeks in 2001 and 2002. Mineralogical analysis was conducted using X-ray Diffraction, Scanning Electron Microscopy, and Electron Microprobe. Chemical analysis was conducted using ICP-AES. Analyses to date indicate the precipitates contain up to 70% Fe, 5% Zn, 5.5% SO4, and are ferrihydrite ± schwertmannite. Compositions of the mineral- and aqueous phases will be used as input to the chemical-equilibrium model, PHREEQC. The model simulations will be used to determine whether the precipitate is in equilibrium with the surface water of each creek. The results of this analysis will be incorporated into more complex, integrated geochemical and hydrological models to estimate pre-mining surface water quality in mineralized areas. This study will contribute to the overall goals of the project, which are to: develop and evaluate a model to predict background water quality in mineralized areas; determine the water quality in Red Dog Creek prior to disturbance in 1988; and determine the affect of the Fe-hydroxide precipitate on water quality.