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Greaser, K.K., 2004

Modeling solid-water interactions in mineralized areas: An example from Red Dog, Alaska

Bibliographic Reference

Greaser, K.K., 2004, Modeling solid-water interactions in mineralized areas: An example from Red Dog, Alaska: Golden, Colorado, Colorado School of Mines, Ph.D. dissertation, 175 p., illust. (some color), map.


This project investigated two acid rock drainage sites in Alaska, 965 km northwest of Anchorage. The Ikalukrok Creek-Alvinella Showing (ICAS) and the Cub Creek Showings (CCS) are exposures of sulfide mineralization 10 km northwest of the Red Dog Mine. Weathering and erosion of the WAS results in the formation of a red precipitate that coats the bottom of the Ikalukrok Creek for more than 30 km downstream. Cub Creek is coated with alternating layers of hardened red and cream precipitate. The first objective of this research was to describe the spatial and temporal changes in stream water and precipitate chemistry of the ICAS and the CCS. The second objective was to geochemically model the solid-water interactions in the two streams. This modeling would test the applicability of the laboratory-derived, single-solute sorption constants calculated by Dzombak and Morel (1990) to natural systems. The data from the two sites included stream and precipitate samples collected approximately every two weeks during the 2002 flow season. Chemical, X-Ray Diffraction and Scanning Electron Microprobe data indicated the precipitate at the ICAS is the iron oxyhydroxide ferrihydrite. The same analyses on the precipitate at the CCS produced inconclusive results. The red precipitate appears to be ferrihydrite, while the cream precipitate may be ferrihydrite mixed with diadochite (Fe2 (PO4)(SO4)(OH) · 5H2O). Both minerals may have been bacterially precipitated at the CCS. Geochemical modeling of solid-water interactions at the ICAS indicate the single-solute sorption constants calculated by Dzombak and Morel (1990) were of limited use in predicting solid phase composition. Fourteen water/precipitate sample pairs were used to develop empirical constants. These constants are statistically different than the single-solute constants. The most likely reason for the difference between the laboratory-derived constants and the empirical constants is temperature. Geochemical modeling of the ferrihydrite collected at the CCS indicates the composition is not only affected by low temperatures but also bacteria. This study indicates temperature is a primary control on sorption that should be considered in remediation and also highlights the need for detailed studies of the composition and mineralogy of precipitates as a part of baseline studies for mines.

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