THE ROLE OF INSTREAM PROCESSES IN BUFFERING THE SURFACE WATER QUALITY DRAINING ZN-PB-FE SULFIDE DEPOSITS IN THE BROOKS RANGE, NORTHWEST ALASKA

Weathering of surface-exposed rocks containing high concentrations of metals may adversely affect water, soil, and sediment quality. This natural degradation of the environment has been occurring for millions of years in mineralized areas. 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.

This project will study the surface water chemistry of Red Dog and Ikalukrok Creeks, northwest Alaska. Prior to mining, Red Dog Creek eroded three surface deposits comprising the Red Dog Mine located 965 km northwest of Anchorage. Ikalukrok Creek erodes the Alvinella showing, an unmined deposit 9 km northwest of Red Dog. Each deposit is composed of Zn-Pb-Fe sulfides.

Processes affecting surface-water quality that will be studied include rock-water interactions, climate affects, and instream processes including the affects of the prominent red precipitate present in these streams.

Three objectives of the project are: 1) to develop and evaluate a model to predict background water quality in mineralized areas; 2) determine the water quality in Red Dog Creek prior to disturbance in 1988; and 3) determine the metal-buffering capacity of the precipitate and its affect on water quality.

Data gathering for the project began summer 2001. Field work included determination of an applicable analog deposit to Red Dog (the Alvinella showing), and collection of water and precipitate samples from the analog deposit. Laboratory work will include mineralogical analysis of the precipitates using Electron Microprobe, SEM, and XRD; column weathering tests of the ore at Red Dog and Alvinella; and mixing experiments to create precipitates similar to those observed at the analog deposit. Modeling will incorporate hydrological and geochemical processes affecting the water quality in Red Dog and Ikalukrok Creeks. Models to be used include Geochemist’s Workbench, PHREEQC, PHAST, MIKE SHE, and MODFLOW.

This presentation will include methodology and current results.