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

Paper No. 1
Presentation Time: 8:00 AM


FOSTER, Andrea L., U.S. Geol Survey, 345 Middlefield Rd. MS 901, Menlo Park, CA 94025, MUNK, LeeAnn, Geological Sciences, Univ of Alaska Anchorage, 3211 Providence Drive, Anchorage, AK 99508, KOSKI, Randolph A., U.S. Geol Survey, 345 Middlefield Road, MS901, Menlo Park, CA 94025, SHANKS, W.C., U.S. Geological Survey and STILLINGS, Lisa L., U.S. Geol Survey, MS-176, University of Nevada-Reno, Reno, NV 89557-0047, afoster@usgs.gov

High-grade copper ore was mined from volcanogenic massive sulfide deposits located on the shorelines of islands and fjords of Prince William Sound (PWS) in the early 1900s. The wet climatic conditions of southern Alaska have resulted in extensive weathering of sulfide- and metal-rich mine waste and rusting of the metal debris left at the abandoned mine sites. In some localities, sulfide oxidation is intense enough to generate acidic, metal-rich plumes of groundwater that migrate through the intertidal zone. Other localities do not appear to be acid-generating. Two of the three sites are characterized by massive microbially-mediated precipitation of Fe oxide.

On Latouche Island, near-neutral, low conductivity water flowing from a mine tunnel at the Beatson site passes through tailings and metal rubble before reaching sea level. Along the way, a variety of biogenic Fe oxide precipitates form. For example, abundant and distinctive blooms of Leptothrix colonies occur in still pools or slow-running water with circumneutral pH. Based on previous experience, we propose that blooms of Leptothrix sequester large amounts of heavy metals at Beatson and other sites in PWS. At the Threeman site in Landlocked Bay, seep waters passing through tailings are circumneutral, but the conductivity of waters is consistently higher than at Beatson. A very different morphology and color of Fe precipitate was observed here relative to those observed at Beatson, along with an unusual occurrence of putative freshwater purple sulfur bacteria whose existence may be supported by sulfate emanating from oxidation of mine waste. Intertidal sediments (mostly tailings and ore) at the Ellamar site in Virgin Bay contain very acidic (pH 2.8-4) porewaters that are saturated with respect to jarosite as evidenced by its precipitation in the subsurface. Microbial communities have not yet been identified in this material, but we suspect that Thiobacilli and other acid-loving sulfur- or iron-oxidizing microbes dominate the microbial community in the Ellamar intertidal zone.