METAL AND TRACE ELEMENT DISTRIBUTION IN WATER AND STREAMBED PRECIPITATES GENERATED FROM WEATHERING OF COPPER SULFIDE TAILINGS, LATOUCHE ISLAND, PRINCE WILLIAM SOUND, ALASKA

The local watersheds near the Beatson, Blackbird, and Duke and Duchess mines on Latouche Island, Prince William Sound (PWS) are receiving elevated concentrations of aqueous metals that originate from weathered copper sulfide ore and waste rock. The dissolved concentrations of metals decrease in the water primarily as a function of change in pH (2.69 to 8.03) and increasing distance away from mined areas. The highest dissolved concentrations of Fe (16.5 ppm), Cu (2,053.2 ppb), and Pb (139.8 ppb) occur in the lowest pH (2.69) water draining from the volumetrically smaller tailings at the Duke and Duchess mine sites. The Blackbird and Beatson mine sites, which have the largest volume of exposed tailings and waste rock of all the mine sites, on Latouche Island have the highest dissolved Zn concentration (1348.0 ppb). The surface water near the Beatson mine site also contains dissolved Fe concentrations ranging from 11.2 to 260.4 ppb and dissolved Cu concentrations ranging from 0.8 to 353.8 ppb.

Iron-rich precipitates occur at all three mine sites as coatings on the streambeds. These precipitates were collected at sample sites where they were found as flocculent material that was easily removed from the streambed surface. The precipitates appear to be forming as the pH of the water increases and the solubility of Fe decreases. To determine the trace metal and elemental composition of the precipitates they were dried, weighed, and leached with 2 N trace-metal grade HCL and the resulting solutions were diluted to a known volume and analyzed by ICP-MS. The acid-leachable fraction of the precipitates is enriched in metals relative to the water by several orders of magnitude. The precipitates are composed primarily of Fe (137.8 to 13,475.3 mg/g), Cu (8.4 to 1,408.6 mg/g), Pb (0.051 to 94.6 mg/g), and Zn (0.024 to 375.6 mg/g). The results reported here are motivation for further studies to investigate the transport of these metal-rich precipitates into the near-shore environment and the potential effects on the aquatic environment.